Category: Study Materials
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Transfer RNA (tRNA): Definition, Structure, and, Function
Continue ReadingThe role of RNA in protein synthesis
1. mRNA: This is a messenger RNA, transfer the genetic detail duplicated from DNA in fashion of a sequence of 3-base code ‘term’, every term states a certain amino acid.
2. Ribosomal RNA (rRNA): It links with a batch of proteins to configure ribosomes. It is the complicated form, moves physically along with a mRNA molecule, facilitates the fabrication of various amino acids into protein chains. They also link tRNAs and different supplementary molecules necessary for protein synthesis. Ribosomes are made up of a large and small subunit, each of which having their unique rRNA molecule or molecules.
3. Transfer RNA (tRNA): It is pivotal in decrypting the key codons in mRNA. Every amino acid possesses their individual kind of tRNA, which attach it and transfer it to the expanding end of a polypeptide chain when the subsequent codon on mRNA needs it. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a 3-base sequence that can pair with base of its reciprocal codon in the mRNA.
About tRNA
Every tRNA carry a set of 3 nucleotides known an anticodon. The anticodon of a said tRNA can attach to one or more particular mRNA codons.
The codons are predetermined for the tRNA thus, transferring the amino acid to that specific location.
Variety of tRNA are streaming within a cell, possessing their own anticodon along with complimentary amino acid and they attach to codons inside of the ribosome, where they remit amino acids for incorporation into the protein chain.
Thus, proteins are constructed from miniature units known as amino acids, which are described by 3-nucleotide mRNA sequences called codons.
The 3D Structure of tRNA
A tRNA is formed from a single strand of RNA in a similar fashion mRNA is formed.
However, the strand takes on a complex three dimensional structure since base pairs form between nucleotides in different parts of the molecule.
This creates double-stranded regions and loops, overlapping the tRNA into an L shape.
The tRNA molecule has a noticeable folded structure with 3 hairpin loops that form the structure of a 3-leafed clover.
One of these hairpin loops contains a sequence known as the anticodon, which can admit and decode an mRNA codon.
Every tRNA have their correlated amino acid attached to its end.
When a tRNA identifies and attaches to its corresponding codon in the ribosome, the tRNA shifts the suitable amino acid to the tip of the lengthening amino acid chain.
Then the tRNAs and ribosome carry on to decipher the mRNA molecule until the entire series is translated into a protein.
tRNA and its Decoding Role
The genetic information passed from DNA to protein via mRNA in which the nucleotide sequence of mRNA is converted into chain of the amino acid to form protein.
However, this deciphering procedure is carried out with the help of two kinds of adapter molecules: tRNAs and an enzymes known as aminoacyl-tRNA synthetases.
There are 2 functions which are performed by all tRNAs:
1. To get chemically connected to a specific amino acid and to base-pair with a codon in mRNA so as to put in the amino acid in the lengthening peptide chain.
Every tRNA molecule is exquisitely identified by the 20 aminoacyl-tRNA synthetases.
In a similar fashion, every enzyme molecules inimitably attaches the 20 amino acids to a specific tRNA, forming an aminoacyl-tRNA.
2. When the accurate amino acid is linked, then a tRNA identifies a codon in mRNA, thereby bringing its amino acid to the expanding polypeptide.
How Synthetases Recognize tRNAs.
After further studies on tRNA, 30 – 40 variety of tRNAs were recognized in bacterial cells while about 50 – 100 in animal and plant cells.
Therefore, the count of tRNAs in almost all cells is exceeding the number of amino acids observed in proteins.
Moreover, they differ from the number of codons in the genetic code.
Accordingly, several amino acids possess more than one tRNA to which they can link.
Furthermore, several tRNAs can attach to more than one codon. Aforementioned, the majority of amino acids are encoded by more than one codon, needing some tRNAs to identify more than one codon.
Function of tRNA Molecules
The function of 70 – 80 nucleotides long tRNA is based on their accurate 3D structures.
In solution, all tRNA molecules overlap into a same stem-loop setting that mimic a cloverleaf which when drawn in two dimensions.
The 4 stems are small double helices fixed by Watson-Crick base pairing; 3 out of 4 stems have loops containing 7 or 8 bases at their tail end, whereas the rest, unloop stem embody the free 3′ and 5′ ends of the chain.
3 nucleotides entitled the anticodon, located at the middle of one loop, can form base pairs with the 3 corresponding nucleotides forming a codon in mRNA.
As delineated earlier, determined aminoacyl-tRNA synthetases identifies the surface structure of every tRNA for a particular amino acid and covalently bind the specific amino acid to the unloop amino acid acceptor stem.
The 3′ terminal end of each tRNAs has the sequence CCA, which in most instance adjoins when synthesis and processing of the tRNA are finish.
Observed in 3 dimensions, the overlapped tRNA molecule has an L shape with the anticodon loop and acceptor stem forming the ends of the two arms.
Loading tRNA With an Amino Acid
Enzymes known as aminoacyl-tRNA synthetases have this pivotal role.
There is an individual synthetase enzyme for each amino acid, wherein an enzyme recognizes only particular amino acid with its respective tRNAs.
Whenever the amino acid and its tRNA binds its respective enzyme, the enzyme blends them together.
The above reaction has been powered by the “energy currency” molecule adenosine triphosphate (ATP).
Sometimes, an aminoacyl-tRNA synthetase miscalculate, wherein it attaches to the incorrect amino acid.
For instance, the threonine synthetase occasionally seize serine by coincidence and binds it to the threonine tRNA.
Fortunately, the threonine synthetase has a proofreading site, which dislodges the amino acid from the tRNA.
tRNA Summary
Genetic information is transmitted into mRNA in the form of a triplet code.
Every amino acid is encoded by surplus of 3 – base sequences, or codons, in mRNA.
Each codon identifies one amino acid, however, majority of amino acids are encoded by multiple codons.
All tRNAs have a same 3 – D structure that comprises an acceptor arm that binds a particular amino acid and a stem-loop with a 3- base anticodon sequence at its ends.
The anticodon can base-pair with its complimentary codon or codons in mRNA.
Since it is a nonstandard interplay, a tRNA may base-pair with more than one mRNA codon, and in contrast, a specific codon may base-pair with several tRNAs.
Each of the 20 aminoacyl-tRNA synthetases identifies a single amino acid and covalently links it to an associated tRNA, producing an aminoacyl-tRNA.
This reaction triggers the amino acid, so it can involve in peptide-bond development.
Transfer RNA (tRNA) Citations
- tRNA Modifications: Impact on Structure and Thermal Adaptation. Biomolecules . 2017 Apr 4;7(2):35.
- tRNA biology charges to the front. Genes Dev . 2010 Sep 1;24(17):1832-60.
- Transfer RNA: From pioneering crystallographic studies to contemporary tRNA biology. Arch Biochem Biophys . 2016 Jul 15;602:95-105.
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Green Revolution: Definition, Advantages, Importance, & Facts
Continue ReadingWhat is Green Revolution?
Green Revolution is really the way toward expanding agrarian creation by utilizing present day machines and procedures.
It was a logical exploration-based innovation drive performed among 1950 and the last part of the 1960s, that expanded horticultural creation around the world, especially in the creating scene, starting most uniquely in the last part of the 1960s.
It utilized HYV seeds, expanded utilization of manure and more specialized techniques for water system to build the creation of food grains.
Green Revolution in India
In India Green Revolution started in the mid 1960s that prompted an expansion in food grain creation, particularly in Punjab, Haryana, and Uttar Pradesh.
Significant achievements in this endeavor were the advancement of high-yielding assortments of wheat.
The Green revolution is revolutionary in character because of the presentation of new innovation, groundbreaking thoughts, the new use of data sources like HYV seeds, composts, water system water, pesticides, and so on.
As every one of these were brought out of nowhere and spread rapidly to accomplish sensational outcomes subsequently it is named as a revolution in green agribusiness.
Reason Behind Green Revolution
The world’s most exceedingly awful recorded food debacle occurred in 1943 in British governed India known as the Bengal Famine.
An expected 4,000,000 individuals died of yearning that year alone in Eastern India (that incorporated the present Bangladesh).
The underlying hypothesis set forward to clarify that disaster was that there was an intense shortage in food creation nearby.
Notwithstanding, Indian financial analyst Amartya Sen (beneficiary of the Nobel Prize for Economics, 1998) has set up that while food lack was a supporter of the issue, a more strong factor was the aftereffect of madness identified with World War II which focused on food supply for the British rulers.
The insanity was additionally misused by Indian merchants who accumulated food to sell at more exorbitant costs.
By and by when the British left India four years after the fact in 1947, India kept on being spooky by recollections of the Bengal Famine.
It was in this way normal that food security was a vital thing on free India’s plan. This mindfulness drove, on one hand to the Green Revolution in India and on the other, administrative measures to guarantee that financial specialists could always again be unable to store nourishment for reasons of benefit.
Notwithstanding, the expression “Green Revolution” is applied to the period from 1967 to 1978. Somewhere in the range of 1947 and 1967, endeavors at accomplishing food independence’s were not totally fruitful.
Endeavors until 1967 to a great extent focused on growing the cultivating regions. Be that as it may, starvation passings were all the while being accounted for in the papers.
In an ideal instance of Malthusian financial matters, populace was developing at a lot quicker rate than food creation. This called for extreme activity to expand yield. The activity came as Green Revolution.
The expression “Green Revolution” is an overall one that is applied to fruitful rural analyses in numerous Third world nations. It’s anything but explicit to India. However, It was best in India.
Factual Results of Green Revolution
A record grain yield in 1978-79 around 131 million tons happened because of the Green Revolution. Consequently, it made India as one of the world’s greatest agrarian maker.
In India Green Revolution recorded a significant degree of accomplishment. India likewise turned into an exporter of food grains around that time.
Monetary Results of Green Revolution
Yield regions under this venture required more water, more composts, more pesticides, and certain different synthetic substances.
This expanded the development of the nearby assembling area. Expanded modern development made new positions and added to the nation’s GDP.
The expansion in water system made the requirement for new dams to saddle storm water. The put away water was utilized to make hydro-electric force.
The entirety of this brought about modern development, made positions and worked on the personal satisfaction of individuals in towns.
Sociological Results of Green Revolution
This new innovation utilized regular use of water, composts, bug sprays, bigger volumes of transportation, power, and so on The agrarian specialists as well as modern laborers landed a lot of positions on account of the production of offices like processing plants, hydro-electric force stations, and so on to back up the revolution.
Political Results of Green Revolution
Quite possibly the main factors that made Mrs. Indira Gandhi (1917-1984) and her gathering the Indian National Congress, an extremely incredible political power in India is this Green Revolution. India changed itself from a destitute country to an exporter of food.
This gave India adoration and appreciation from everywhere the world, particularly from the Third world country.
Disservices of the Green Revolution
The negative social impact of the Revolution was additionally soon noticeable. Differences in pay have been augmented by these advancements in horticulture.
Rich landowners have power over the horticultural info and worked on synthetic composts.
The most noticeably terrible part is that the helpless ranchers wound up impeded by little homesteads of land and insufficient water supply. With complete horticultural methods and data sources, the Green revaluation would in general have its most focused application on enormous homesteads.
As a convergence of the new innovation to enormous homesteads, the Inequalities have additionally Increased.
The helpless ranchers have been unfavorably influenced by a developing propensity among the rich ranchers to recover land recently rented out under tenure understanding, which has been made beneficial by better yields from new innovation.
Poor people and in reverse class of ranchers has been progressively driven into the position of the landless worker.
An intense expansion in a more elevated level of lease with land esteem taking off.
Likewise in light of unnecessary utilization of manures soil began to become soluble or acidic relying on the idea of the compost utilized.
Conclusion
India has made a colossal accomplishment in term of the Green Revolution, as it’s anything but an extraordinary degree of food security.
It’s anything but countless needy individuals out of destitution and aided numerous non-needy individuals keep away from the neediness and yearning they would have encountered had it not occurred.
This revolution has saved over a billion group everywhere on the world from starvation.
Green Revolution Citations
- The green revolution. Nutr Rev . 1969 May;27(5):133-6.
- From green to gold: agricultural revolution for food security. J Exp Bot . 2020 Apr 6;71(7):2211-2215.
- A Strigolactone Biosynthesis Gene Contributed to the Green Revolution in Rice. Mol Plant . 2020 Jun 1;13(6):923-932.
- Toward a “Green Revolution” for Soybean. Mol Plant . 2020 May 4;13(5):688-697.
- Green revolution: impacts, limits, and the path ahead. Proc Natl Acad Sci U S A . 2012 Jul 31;109(31):12302-8.
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Cytoplasm: Definition, Function, and Examples
Continue ReadingWhat is Cytoplasm?
Cytoplasm is the liquid matrix of the cell in which the membrane bound organelles such as Mitochondria, Golgi Apparatus ribosome, nucleus and other chemical components proteins, Glucose, Lipids.
The cytoplasm was first discovered by Anton Von Leuwenhoek and termed by Kolliker in 19th century.
Though cytoplasm is a liquid component the diverse make of the components provides a structural organization and the components are sequentially arranged and are well synchronized.
The cytoplasm is an indicator to the outside environment and changes the activity of the cell frequently to maintain HOMEOSTASIS.
Characteristic of Cytoplasm
1. Cytoplasm is a well – organized liquid matrix:
Earlier it was considered as a part of protoplasm but invention of Electron Microscopes provided a depth of knowledge regarding the organization of cytoplasm inside the cell.
2. The movement of matrix is well programmed:
Based on the cell’s necessity, transportation of enzymes, proteins and other substances which are required at different part of the cell.
3. Cytoplasm is the internal milieu of the cell:
They act as regulators maintaining a cell’s vital survival function even the external factors disrupt the homeostatic function and maintain the internal environment.
4. Maintains the integrity of the cell:
The cell shape, movement, protein synthesis and other metabolic activities are governed by the cytoplasm.
5. High viscosity matrix and colloid:
The thickness of the matrix is usually higher than that of water. Higher the viscosity easier the organelles can suspend. Because of the suspension of the organelles the matrix is colloid.
Components of Cytoplasm
Cytoplasm has both solid and liquid components of Cytoplasm.
Solid Components are
1. Organelles bound by two membrane
a. Plastids – special feature present only in plant cell has a variety of types and function. The 2 types are Leucoplasts and Chromoplasts.
i. Leucoplasts are colorless components which have their role in storage and metabolism of starch.
ii. Chromoplasts are colored compound mainly green in plants forming the chloroplasts which are essential in photosynthesis.
b. Mitochondria – Power house of the cell provides energy in ATP from the cellular respiration.
2. Organelles Bound by one membrane
a. Peroxisomes – Peroxisomes are protective in function producing peroxides
b. Vacuoles – Specialized feature present in plants where the food molecules are stored for metabolism when needed.
3. Ribosomes – Ribosomes are molecular compounds which is involved in formation of protein for cell structural function.
4. Endomembrane system – consists Endoplasmic Reticulum, Golgi Apparatus and Nuclear Envelope
5. The endomembrane system constitutes the internal membrane providing organelle free matrix for cell survival.
The endoplasmic reticulum arises from the nucleus extends throughout the length and reaches plasma membrane forming the endomembrane.
I. Nuclear envelope: Nuclear Envelope is made up of flattened cisternae like discs. Many discs come together forming a small pore which allows a contact between cytoplasm and nucleus.
The outer membrane contacts endoplasmic reticulum and the inner membrane has had thread of chromatin molecule.
II. Endoplasmic Reticulum (ER) is the major constituent of the endomembrane system. They are tubule and flattened that carries out the function of storage.
The ER is of 2 types:
a. Rough Endoplasmic Reticulum
b. Smooth Endoplasmic Reticulum protein synthesized are stored at RER but transported through SER.
Their main function remains secretion.
III. Golgi Complex flattened stack of disc from dictyosomes forms the determined structure.
Golgi Bodies are concerned with packaging and storing of the secretory molecule and then vesicles are pinched off from Golgi complex through exocytosis.
6. Cytoskeleton
I. Micro tubules – Microtubules are thin and rigid structures made up of 13 filaments. Protein component is the main structural source for the tubule structure is contributed by Tubulin.
They are easily depolymerized and can shape and function of any cell by contributing to Cell division providing spindle fibers, Asters, Locomotion etc.,
II. Centrioles – cylindrical structure and paired. They migrate to animal pole during cell division
III. Basal Bodies – a structure similar to centrioles are present at the bases of cilia or flagella. Cilia and Flagella both has a common arrangement of microtubule (9 + 2). These are used in order for locomotion purposes.
IV. Microfilaments – are smallest structure made up of actin associated with myosin and other aiding proteins which help in contraction thereby causing motility of the organism.
V. Intermediate Filaments – they are mechanical in function
Liquid components are:
1. Cytosol – A liquid component comprises the structural organelles of cell. They are present inside the cell. Responsible for movement and integrity.
2. Hyaloplasm – is the ground cytoplasm which does not have any structural component. They are present outside the endomembrane system.
Their main role is to regulate the internal milieu. This is also called as Ground cytoplasm / Cytoplasmic matrix proper.
Other components Excretory products, Metabolic storage, Secretory materials
Cytoplasm: Plant vs Animal Cells
The difference between plant and animal cell cytoplasm is negligible as the cytoplasm has common role in both cell types.
The main difference will be the presence and absence of organelles present in them such as vacuoles, chloroplasts etc.,
Significance of Cytoplasm
1. Microtubules specifically locate and guide the enzymes. Precise positioning information is provided for the enzymes to catalyst the biosynthesis.
2. The ER is related to the formation of glyoxysomes and vacuoles
3. Golgi Complex is distributed in the cytoplasm in the form of dictyosomes.
4. Cytoplasmic Streaming – Also known as CYCLOSIS, is a process where the cell components are circulated inside the matrix for maintain the process of homeostasis.
The streaming is influenced by the pH, temperature and various other factors which modify the body’s homeostatic condition.
For Example: Sunlight falls on a particular spot of the plant. The other regions lack sunlight here the cytoplasmic streaming with the help of microtubules and filaments the chloroplast is moved to sun receiving regions.
5. The structural integrity, motility, shape are all maintained by the Cytoplasm.
Cytoplasm Citations
- Consequences of phase separation in cytoplasm. Int Rev Cytol . 2000;192:331-43.
- The periplastidal compartment: a naturally minimized eukaryotic cytoplasm. Curr Opin Microbiol . 2014 Dec;22:88-93.
- How crowded is the cytoplasm? Cell . 1982 Sep;30(2):345-7.
- Molecular pathways involved in the transport of nuclear receptors from the nucleus to cytoplasm. J Steroid Biochem Mol Biol . 2018 Apr;178:36-44.
- Cytoplasm’s Got Moves. Dev Cell . 2021 Jan 25;56(2):213-226.
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Glucose Oxidation Respiratory Balance Sheet
Continue ReadingAbout Glucose Oxidation Respiratory Balance Sheet
Respiratory balance sheet is a mathematical calculation of net ATP produced by cellular respiration during glucose oxidation which includes Glycolysis, Krebs Cycle and Oxidative Phosphorylation under aerobic condition utilizing one glucose molecule.
Features of Glucose Oxidation Respiratory Balance Sheet
Certain assumptions were considered while forming the balance sheet:
1. For an oxidizing Glucose molecule, it must follow the cellular respiration process in a sequence such that glucose must follow every step of glycolysis to form 2 molecules of pyruvate.
Pyruvate must enter Krebs Cycle to produce reducing equivalents.
The reducing equivalents from Glycolysis and Krebs cycle must enter Electron Transport Chain where they get converted into ATP.
2. Reducing equivalents such as the NADH must carried to Electron Transport Chain in mitochondria
3. The intermediates formed during the oxidization of glucose should not participate in any biosynthesis process to form other products such as Amino acids, Purines pyrimidines or porphyrins.
4. The cellular respiratory substrate must only be GLUCOSE other substrates must not be considered.
Considering the dynamic nature of our cell and living system the above assumptions do not apply practically for a working cell. The balance sheet assumptions are theoretically accepted and followed.
Glucose Oxidation Respiratory Balance Sheet
When NADH produces 3 ATP and FADH2 produces 2 ATP
Respiration Process Direct Synthesis In ETC ATP Consumed Net Gain NADH+FADH2 Glycolysis 4 6+Nil 2 8 Krebs Cycle 3 18+4 Nil 24 Acetyl CoA Formation Nil 6+Nil Nil 6 Total Gain 6 30+4 -2 38 When NADH produces 2.5 ATP and FADH2 produces 1.5 ATP
Respiration Process Direct Synthesis In ETC ATP Consumed Net Gain NADH+FADH2 Glycolysis 4 5+Nil 2 7 Krebs Cycle 2 15+3 Nil 20 Acetyl CoA Formation Nil 5+Nil Nil 5 Total Gain 6 25+3 -2 32 Under Anaerobic respiration, the pyruvic acid converts to lactic acid producing only 6 ATP.
The list of reactions which produced direct ATP synthesis and reduced equivalents are given below:
Glucose Oxidation: Glycolysis
1. Glyceraldehyde 3 Phosphate + NAD → 1,3 – diphosphoglycerate + NADH
Enzyme: Glyceraldehyde – 3 phosphate dehydrogenases
2. 1,3 diphosphoglycerate +ADP + Pi → 3 – phosphoglycerate + ATP
Enzyme: Phosphoglycerate Kinase
3. Phosphoenol pyruvate + ADP + Pi → Pyruvate + ATP
Enzyme: Pyruvate Kinase
These 3 reactions take place twice therefore they produce 4 ATP + 2 NADPH = 4 + 2 (3) = 10
Two other reaction consumes ATP
1. Glucose + ATP → Glucose 6 phosphate + ADP + Pi
Enzyme: Hexokinase
2. Fructose 6 Phosphate + ATP → Fructose1,6 diphosphate + ADP + Pi
Enzyme: Phosphofructokinase
ATP consumed is 2. Therefore, Glycolysis as a whole provides 8 ATP.
Under Anaerobic condition:
2Pyruvate + 2NAD → 2Lactate/ethanol + 2NADH → 6 ATP
Glucose Oxidation: Citric Acid Cycle
1. 2 Pyruvate + 2 NAD → 2 Acetyl Co – A + 2 NADH
Enzyme: Pyruvate Dehydrogenase
2. 2 Isocitrate + 2 NAD → 2 Oxalosuccinate + 2 NADH
Enzyme: Isocitrate Dehydrogenase
3. 2 α – ketoglutarate + 2 NAD → 2 Succinyl Co – A + 2 NADH
Enzyme: α – ketoglutarate Dehydrogenase
4. 2 Succinyl Co – A + 2GDP + 2Pi → 2 Succinate + 2GTP
Enzyme: Succinate Thiokinase
5. 2 Succinate + 2FAD → 2Fumarate + 2FADH2
Enzyme: Succinate Dehydrogenase
6. 2 Malate + 2 NAD → 2 oxaloacetate + 2 NADH
Enzyme: Malate Dehydrogenase
2 pyruvate molecules undergo complete oxidation and provide 30 ATP molecules.
Glucose Oxidation Citations
- Respiratory metabolism: glycolysis, the TCA cycle and mitochondrial electron transport. Curr Opin Plant Biol . 2004 Jun;7(3):254-61.
- The effect of selenium-deficiency on rat fat-cell glucose oxidation. Biochem J . 1983 Aug 15;214(2):471-7.
- Ascorbic acid and glucose oxidation by ultraviolet A-generated oxygen free radicals. Invest Ophthalmol Vis Sci . 1996 Jul;37(8):1549-56.
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Citric Acid Cycle: an Overview, Mechanism, and,...
Continue ReadingWhat is Citric Acid Cycle?
Citric Acid Cycle is an essential catabolic cycle of cellular respiration involves pyruvate as an end product from glycolysis to form energy in terms of ATP, NADH and FADH2. Which in further processes to provide ATP.
The Citric Acid Cycle takes place in Mitochondria and are coupled with Electron Transport Chain to produce ATP.
Hence Mitochondria is the power house of the cell. The Citric Acid Cycle was discovered by Hans Kreb in 1937 from animal enzymes.
Therefore, it can be named as the Krebs’s Cycle or Tricarboxylic Acid Cycle (Contains 3 carboxyl group in the component).
Citric Acid Cycle Feature
1. Takes place during aerobic respiration:
Pyruvate under aerobic condition produces energy and under anaerobic condition they undergo a process of fermentation forming lactic acid or alcohol
2. TCA Cycle is irreversible at 3 steps: producing high amount of negative energy.
The 3 steps involve the enzymes: citrate synthase, α – ketoglutarate dehydrogenase and isocitrate dehydrogenase.
3. Pyruvate; an end product of glucose metabolism; is transported from cytosol to mitochondria to become Acetyl Co – A.
Pyruvate is transported to mitochondria through Voltage gated channel crossing outer mitochondrial membrane. Mitochondrial Pyruvate Carrier then takes pyruvate through Inner Mitochondrial Membrane.
Pyruvate Dehydrogenase Complex; an enzyme oxidizes Pyruvate to form Acetyl Co – A.
4. Cycle involves C6 to C4 in a series of steps:
Tricarboxylic Acid (C6 – 6 carbon compound) is formed by the combination of Acetyl Co – A (C2) and Oxaloacetate (C4).
Condensation process takes place between Oxaloacetate and Acetyl Co – A to form C6 compound.
Further the C6 compound catabolize to produce reduced equivalents (NADH, FADH2).
Oxaloacetate + Acetyl Co – A à Citrate (C6)
5. Eight enzymes are involved in 4 oxidations:
On each oxidation, number of carbo atoms present reduces gradually leaving out C4 compound. C4 the condense to form C6 and he cycle continues.
6. Two sources for Acetyl Co – A:
Acetyl Co – A is not only derived from Glycolysis. Fatty Acid oxidation also provides Acetyl Co – A as its direct end product which can be utilized by the Citric Acid Cycle.
7. A cycle with various intermediate forms:
Citric acid cycle forms various intermediates which provides substrates for different biosynthetic process in plants.
For Example: α – keto glutarate forms glutamate which is essential in Nucleic Acid formation
8. Citric Acid Cycle coupled with Electron Transport Chain:
The reduced equivalents from the cycle is directly transported to complexes present in the inner cell membrane of mitochondria to yield ATP.
Mechanism of Citric Acid Cycle
The Citric Acid Cycle has two steps:
1. Pyruvate Decarboxylation
2. Citric Acid Formation
3. TCA Cycle
Step: 1 Pyruvate Decarboxylation
Enzyme Complex involved – Pyruvate Dehydrogenase Complex (combination of enzymes, coenzymes and cofactors)
Pyruvate Dehydrogenase Complex (PDC) consists of 3 enzymes and 3 cofactors.
They are:
a. Pyruvate decarboxylase(E) + Thiamine pyrophosphate (CoF) – Complex 1
b. Dihydrolipopyl Transacetylase (E) + Lipoic Acid (CoF) – Complex 2
c. Dihydrolipopyl Dehydrogenase (E) + Flavin Adenine Dinucleotide (CoF) – Complex 3
The enzyme complex catalyses the oxidation reaction of Pyruvate to Acetyl Co – A inside the mitochondria with the release of CO2 and reduction of NAD → NADH2
Step: 2 Citric Acid Formation
Enzyme: Citrate Synthase This step is the 1st step of the Citric Acid cycle
I – Citric Acid, a six-carbon compound is formed by condensation and hydrolysis. Acetyl Co – A and Oxaloacetic Acid combines along CH3 and COO- group of acetyl Co – A and Oxaloacetic Acid respectively. On hydrolysis, Coenzyme A is released and Citric Acid is formed.
Step: 3 TCA Cycle
Citrate is the tricarboxylic compound from which the cycle proceeds.
II – Formation of Isocitrate
Enzyme: Aconitase
Enzyme aconitase mediates dehydration and rehydration of citrate molecule forming an isomer of citrate which is isocitrate.
III – α – Ketoglutarate Formation
Enzyme: Isocitrate Dehydrogenase
Dehydrogenase is associated with oxidation of the isocitrate to form α – ketoglutarate with a release of CO2 and formation of carboxyl group. This oxidation involves a reduction of NAD → NADH2. The six – carbon compound now becomes five carbon compound (C5).
IV – Succinyl Co – A synthesis
Enzyme: α – Ketoglutarate Dehydrogenase Complex
The enzyme functions similarly to that of Pyruvate Dehydrogenase accounts for the oxidation of α – Ketoglutarate to Succinyl Co – A. CO2 is released and NAD → NADH2. In this step 4 the five – carbon compound reduces to four – carbon compound (C4).
V – Succinate
Enzyme: Succinyl Co – A synthase
The mitochondrial matrix provides a phosphate group to be attached to the Co – A releasing Coenzyme from the compound. On hydration (i.e. addition of water) succinate is formed. ADP → ATP
VI – Fumarate
Enzyme: Succinate Dehydrogenase
The enzyme catalysis the formation of Fumarate by reducing FAD → FADH2. A double bond is formed between 2nd and 3rd carbon.
VII – Malate
Enzyme: Fumarase
Adding Fumarase and hydrating Fumarate results in the formation of Malate.
VIII – Oxaloacetate formation
Enzyme: Malate dehydrogenase
As dehydrogenase is coupled with formation of reduced equivalents, oxaloacetate is formed by reducing NAD → NADH2. This is the last and the fourth oxidation step in the TCA cycle.
Significance of Citric Acid Cycle
1. Citric Acid Cycle mainly provides ATP as energy. This is the important function of the citric acid cycle.
Acetyl Co – A + FAD + 3 NAD + ADP + H2O →
→ CO2 + ATP + 3 NADH + FADH + Co – A
One NADH = 3 ATP
One FADH2 = 2 ATP
ATP = 1
Total = 3(3) + 2 + 1 = 9+2+1 = 12
Citric Acid Cycle provides 12 ATP but glycolysis produces 2 pyruvate molecule the above calculation accounts only for one cycle of pyruvate.
Two cycle of Citric Acid then provides 2(12) = 24 ATP molecules
2. Citric Acid cycle is Amphibolic. Amphibolic means a process or a reaction which can be both Catabolic and Anabolic.
Catabolic nature is the breakdown of pyruvate for energy.
Anabolic nature is that the intermediates of Citric Acid Cycle can be used for the synthesis of amin acids, purine, porphyrin and pyrimidines
3. As Citric Acid cycle provides intermediates for synthesis of amino acid, purines etc., the cycle cannot run in a proper way.
To make the cycle to run in a proper way, many replenishing reactions are taking place to fill the missing intermediates. This process is called the anaplerosis.
4. Citric Acid cycle is the final common oxidative for energy production of carbohydrates, lipids and proteins.
Citric Acid Cycle: Animal vs Plant Cells
The main difference is the enzyme Succinyl Co – A in animals involves the formation “GTP” whereas plants involves in the formation of “ATP”.
Citric Acid Cycle Citations
- Citric acid cycle and role of its intermediates in metabolism. Cell Biochem Biophys . 2014 Apr;68(3):475-8.
- Impaired Citric Acid Cycle in Nondiabetic Chronic Kidney Disease. EBioMedicine . 2017 Dec;26:6-7.
- Citric acid cycle redux. Trends Biochem Sci . 1990 Nov;15(11):411-2.
- Citric acid cycle intermediates in cardioprotection. Circ Cardiovasc Genet . 2014 Oct;7(5):711-9.
- The key role of anaplerosis and cataplerosis for citric acid cycle function. J Biol Chem . 2002 Aug 23;277(34):30409-12.
- Regulation of leukocyte function by citric acid cycle intermediates. J Leukoc Biol . 2019 Jul;106(1):105-117.
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Growth Factors: Definition, Types, and Examples
Continue ReadingWhat are Growth Factors?
An irreversible, progressive change in a living being for a particular time according to the availabilities of the essential internal and external factors is growth.
In plant’s life term the growth is unlimited and continuous when optimal conditions are present.
Plant growth consists of development of the zygote to seed, on appropriate condition seed germinate to form root and shoot.
Proceeding from then seeds differentiates into different system of a plant bearing different functions.
Development and growth of a plant depend completely upon seed health and the external, internal factors aiding its growth.
Growth factors influence each stage of development by determining the availability of essential nutrients, climate etc., which are external and hormonal synthesis, physiological maintenance, availability of enzymes and substrate for metabolic process etc., are internal.
Growth efficiency is high when internal and external factors are available in essential level and are synchronous with each other enhancing the growth of an organism.
Type of Growth Factors
Growth factors are common for all plant species but the optimal requirement for each species differ making each species unique and distinct.
The common factors affecting the plant growth are divided into;
A. External Growth Factors
(i) Biotic Growth Factors: interaction of plants with other plants their response are all the biotic factors.
(ii) Abiotic Growth Factors: interaction of plants with external non – living factors playing crucial role in plant growth and development
B. Internal Growth Factors
(i) Genetic Growth Factors: the hereditary material made of nucleic acid which assigns different protein molecule for different functions are the genetic factors.
(ii) Physiological Growth Factors: Mainly includes the hormones and enzyme present within the body and the plant requirement.
A. External Growth Factors
External growth factors are components which influence the growth of plants from outside the plant body.
(i). Biotic Growth Factors: biotic factor which influences the plant growth from external sides are just interaction of plants to other plants and competition among themself for the survival of them. These are managed by certain behaviors namely;
Mutualism, Herbivory, Parasitism
a. Mutualism: the interaction between plants for their cooperative mechanism for survival and yielding benefit to each other.
Example: lichens
b. Herbivory: it is the nature of animals where it depends upon plants for survival. When excessive grazing tales place other organism inhabiting the same region has low survival rate.
c. Parasitism: interaction between two organisms where one benefits from the interaction others not and are deprived from nutrition making it hard to survival.
(ii). Abiotic Growth Factors: Factors which does not involve biologically but are essential for growth. Different factors that influence the plant growth are:
a. Climate: each plant has its suitable climate at which they grow well. The climatic factors include: Precipitation, Temperature, Humidity, Solar radiation, Wind velocity and Atmospheric gasses.
1. Precipitation: is of all forms such as Rain, Fog, Haze, Dew, Snow, etc., out of which rain fall is crucial in plant growth. Precipitation is completely dependent on the geography of a region. The slopes of Western Ghats receive high rainfall than the plains therefore considering the rainfall plantation crops are grown at the slopes of Western Ghats. Similarly drier regions support drought resistance plants such as sorghum, wheat, millet etc.,
2. Temperature: temperature is determined by the topography of the region. An ideal range for any plant is between 15° C and 38° C. But for the ideal plant growth each species is unique. The temperature also influences other body activity such as diffusion of the gasses, solubility of different materials, etc.,
3. Humidity: Humidity is the presence of water molecule n the form of water vapor. Higher the humidity lowers the rate of transpiration. Hence water accumulates causing decay of plants.
4. Solar Radiation – Light: Respiration is the process where the CO2 consumed to produce O2. This takes place by the process called photosynthesis. Incident of light is essential for synthesis of energy for plants survival. The radiation controlled the situation by determining the temperature of the region.
5. Atmospheric Gasses: in atmosphere the ratio of Carbon, Oxygen and Nitrogen must be balanced properly other wise imbalances can causes destruction to entire living system.
b. Edaphic Growth Factors: is noting but the specificities of soil for plant growth. The soil has several criteria namely: soil moisture, air, temperature, pH, mineral content, organic content and microorganism.
1. Moisture content makes the availability of nutrients to the plant easily attainable.
2. Soil Air provides aeration which removes any accumulation of undesirable gases, remove the dampness of the soil thereby providing an ideal environment which is free from infections.
3. Temperature, affects the physico chemical process taking place inside the soil and keeps the microbial activity under control and prevent microbial accumulation
4. Soil Organism, microbial growth is well associated with root nodules present in the plant where they fix atmospheric nitrogen to fulfil the nitrogen need for plants.
5. Other, factors associate well with the above factors provide an ideal internal environment for plant growth.
B. Internal Growth Factors
Factors which are present inside a plant body which are responsible for the growth of the plant.
The internal factors are a. Genetic factors and b. Physiological factors.
i. Genetic Growth Factor: the hereditary material becomes responsible for the blueprint of the organism, its productivity, survival capacity and others. In plant breeding technology new methods are employed to produce an ideal variety for better yield. Such efficiencies and capacities are present inside the cell and does not require other factors to promote it.
ii. Physiological Growth Factor: physiological factor is the hormonal and other factors which influence the plant growth. The growth of plants are dependent on the GROWTH REGULATORS, which are hormones which promotes or inhibits the growth.
These are done by 5 major hormones:
a. Auxins: enhance the cell elongation, enlargement, phototropism, geotropism, flower, root initiation, development of flower, root, fruit seeds etc.,
b. Gibberellins: affects the enlargement of organism, resisting the growth of plants as a whole.
c. Cytokinin: Cytokinin works along with auxin helps in cell enlargement
d. Ethylene gas: they diffuse easily throughout the body and ripens the fruit, seeds and are present in meristematic tissues,
e. Abscisic acid: intervene the growth promoting effect by reducing the growth promoting factors.
Growth Factors Citations
- The Pivotal Role of Ethylene in Plant Growth. Trends Plant Sci . 2018 Apr;23(4):311-323.
- Auxins as one of the factors of plant growth improvement by plant growth promoting rhizobacteria. Pol J Microbiol . 2014;63(3):261-6.
- Cytokinin signaling in plant development. Development . 2018 Feb 27;145(4):dev149344.
- Plant abiotic stress response and nutrient use efficiency. Sci China Life Sci . 2020 May;63(5):635-674.
- Brassinosteroids: Multidimensional Regulators of Plant Growth, Development, and Stress Responses. Plant Cell . 2020 Feb;32(2):295-318.
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Growth Rates: Definition, Types, and Examples
Continue ReadingWhat is Growth Rate?
Growth is the fundamental characteristics of any organism which is irreversible, progressive and exponential.
Growth is a gradual phenomenon taking place at fixed interval of time and specific for a given species.
The growth mechanism of plant is significant than other organisms where the cells divide throughout their life having an unlimited growth.
Plants have a specialized region called meristem where cells get dedifferentiated to divide and increase the biomass of the plant.
The growth is a quantitative measure over time.
The growth in plants is measured by growth rate which is a measure of increase in growth per unit time.
Types of Growth Rate
Growth rate is of two types and are classified based on cell division
(i) Arithmetic Growth Rate
(ii) Geometric Growth Rate
(i) Arithmetic Growth Rate
In arithmetic growth, following a cell division only a single cell attains the capacity for further division, another cell gets differentiated and matured.
This follows for further division. The division is along one side increasing the length of the plant.
For example: Elongation of root. When plotting a graph for root elongation against time, a linear curve is obtained.
The linear plot indicates the growth rate was arithmetic in nature.
In Arithmetic growth is long one direction.
The Arithmetic Growth is expressed as:
Lt = L0 + rt
Lt : Length at time t
L0 : Initial length at time zero
r : Elongation per unit time
(ii) Geometric Growth Rate
Geometric growth type involves cell division were both daughter cell retains the capability for further division.
The growth is exponential and rapid for a particular period of time and when subjected to external and internal factors, their growth varies.
They represent the overall growth of a plant or a system at a particular period of time.
When plotted against time a sigmoid curve is obtained.
The sigmoid shape represents the rate od growth over a different period of time indicating different phases.
The four phases are: Lag phase, Log Phase, Diminishing Phase and Stationary Phase
1. Lag Phase: the initial growth period is referred as lag phase. In this phase each cell starts to divide continuously and make itself easily available to uptake of nutrients and increase cell mass. The phase involves gradual increase in cell growth.
2. Log Phase: the rapid cell growth period is the log phase. Under Favorable environmental condition the cell growth increases exponentially in large scale by the multiplication of cell division. Simultaneous nutrient input and maturation takes place in this stage. However, the cell division exceeds the maturation
3. Diminishing Phase: the cells start maturation providing a higher yield of cellular metabolites. The growth or new cell formation is confined to certain region of meristems which divides but to keep up with overall plant growth. Reduces the rate of formation of new cells
4. Stationary Phase: A final stage of plant growth where the meristematic regions constantly produce new cells and old cells are removed. This constant maintenance of cell cycle is the Stationary Phase.
This exponential growth can be represented as;
Wl = W0 ert
Wl = Final Size
W0 = Initial size
e = base of natural logarithm
r = growth rate
t = time
r = relative growth rate indicating the efficiency index.
Relative growth rate is the measure of given system per unit time.
This measure is compared with Absolute growth rate, a total measure of plant growth per unit time.
Growth Rate Citations
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Cell Lysis: an Overview, Definition, Types, and...
Continue ReadingWhat is Cell Lysis?
A cell is a biological living unit which is typically an enclosed space containing specialized components called organelles.
The inside of a cell is filled with a fluid called the cytoplasm and the entire cell shape is maintained because of the plasma/ cell membrane.
The cell membrane is semi-permeable and is made up of components that contributes to its structural integrity.
Bacteria also have a cell wall, which provides them with an additional layer of protection.
It is important for the cell to regulate its own functions and prevent any kind of compromise to its morphology.
Cell lysis refers to the breakage of the plasma membrane or the cell wall and leakage of the cellular contents, eventually resulting in cell death.
It is exhibited by both eukaryotic and prokaryotic cells.
Understanding cell lysis is necessary as it can not only help us comprehend the mechanism behind it, we can also exploit those mechanisms for experimental studies.
Lysis is brought about by specialised proteins which compromise the cell membrane, and in case of prokaryotes, the cell wall, or by external agents such as detergents or mechanical means.
Types of Cell Lysis
1. Cytolysis
Cytolysis occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell.
2. Oncolysis
Oncolysis is the destruction of neoplastic cells or of a tumour.
3. Plasmolysis
Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis.
4. Immunolysis
Erythrocytes’ hemoglobin release free radicals in response to pathogens when lysed by them.
Natural Cell Lysis
Cell lysis is exhibited by various types of cells and although the end result is cell death, this mechanism serves to benefit either the causative organism or the host organism.
Described below are some ways in which cell lysis takes place in nature.
a. Virus Mediated Cell Lysis
Bacteriophages are a type of virus which infect bacterial cells and use the latter for their replication and survival.
Bacterial cell lysis due to a viral attack is one of the ways in which the viral particles can be released from the host cell after multiplication.
Since the bacterial cell wall is composed of peptidoglycan (a polymer), specialized proteins called enzymes are released to disrupt the cell membrane and cell wall.
Holin, endolysin and spannin are three such enzymes involved in this mode of lysis.
Holins are the enzymes which control the timing of cell lysis.
They keep accumulating near the cell membrane and when the viral particles are ready to be released outside the cell, they cause the formation of holes in the bacterial cell wall.
Endolysins are the enzymes which can access the cell wall via these holes and actually attack the bonds between the building blocks of peptidoglycan of the cell wall, thereby degrading it.
Spannins disrupt the outermost membrane of the bacterial cell.
Single stranded DNA phages have certain genes that prevent the synthesis of peptidoglycan components and result in a weakened cell wall and causing lysis.
Significance: Viruses increase their infectivity by causing lysis of bacterial cells and releasing their progeny.
b. Cell Lysis in Cell Death Pathways
In mammalian cells, different intracellular pathways are activated when there is a bacterial or viral infection.
Such pathways lead to cell death as that can be beneficial to limit the infection since it would reduce the number of cells required by the foreign organism to invade.
Cell lysis, as described earlier, involves disruption of the cell membrane.
The cell membrane is made up of molecules called phospholipids, which are basically phosphate groups attached to a lipid molecule.
Infection in mammalian cells results in a process called inflammation, which is simply the activation of immune system.
Inflammation results in activation of specialised enzymes called caspases when a cell requires to go into ‘death’.
These caspases activate proteins which can bind to the phospholipids of the cell membrane, form pores and result in cell swelling and lysis.
Significance: Lysis of mammalian cells infected by bacteria/viruses causes reduced infection potential of the latter.
c. Immune Cell Mediated Cell Lysis
Immune cells such as T-cells have the property to recognize foreign bodies called antigens.
They release granules which contain proteins called perforins.
These attack the antigens, cause pore formation and result in bursting of the foreign cells.
Significance: Immune cells can directly kill foreign bodies via cell lysis.
Artificial Methods of Cell Lysis
Experimental research in biology requires studies on cellular components.
Hence, artificial methods of lysing cells have been developed.
Some of those techniques have been described below.
a. Osmotic Cell Lysis
Cells maintain their size due to their surroundings which contain fluids that prevent excess inflow (endosmosis) or outflow or water (exosmosis).
Transferring cells to solutions (example- sucrose) with a different concentration as compared to the cytoplasm can cause endosmosis, causing swelling and lysis.
b. Detergent Mediated Cell Lysis
Detergents are compounds which have both water loving and water hating components, and that makes them an ideal candidate to disrupt the cell membrane.
Example- SDS, Triton-X.
c. Physical Breakage
Beads and rotating blades can cause physical damage to the cell membrane and result in lysis.
Cell Lysis Disease: Hemolytic Anaemia
Red blood cells (RBCs) have a lifespan of 120 days.
In abnormal conditions such as pathogen attack or when the immune cells of the body mistakenly characterize RBCs as foreign cells, the cell membrane of RBCs get disrupted and they die before the end of their lifespan.
This drastically reduces RBC count in the body and results in anaemia.
Applications of Cell Lysis
Cell lysis is a widely used method for intracellular studies.
Proteins, DNA and RNA and extracted by a combination of lysis methods.
Industrially useful products generated in the intracellular space by micro-organisms are also obtained by lysing their cells.
Citations
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Phases of Growth, Growth Rate, and Growth...
Continue ReadingWhat is Cell Growth
Growth is an irreversible, exponential progressive process which results in the increase in the biomass of an organism both quantitatively and qualitatively over a period of time thereby making an organism fit for survival in every better possible way.
Growth is a net result of accumulation of small changes initiating at cellular level and contributing in large scale over a period of time.
Plants show a remarkable feature of infinite cell divisions at the specialized region of meristems where the stem cells are present waiting for an internal stimulator to initiate growth.
When a sapling starts its growth period the meristems were present all over the plant diving continuously and increasing exponentially the number of cells in plant.
Later, the region of meristem gets restricted to specific parts such as the Apex, Laterals, and Intercalary.
Phases of Growth
With appropriate nutrients and favorable environmental condition, a plant undergoes desirable change is gradual steps. The changes initiates from cells forms 3 phases of growth.
They are:
A. Cell Division
B. Cell Enlargement
C. Cell Differentiation
A. Cell Division
The initial process of plant growth is the division of cells by the process of DNA replication and cell growth.
Cell cycle mitosis becomes very essential as it is associated with somatic cell proliferation.
The division takes place in meristems where the stem cell proliferates to increase the length and girth of a plant.
Mitosis involves the 4 stages of cell division producing 2 cells by single division. The four stages are Prophase, Metaphase, Telophase and Anaphase followed by Cytokinesis and G0 Phase (i.e.) Quiescent phase.
The mitosis cycle is dependent on the Cyclin Dependent Kinase (CDK) that regulates the synthesis, replication and cell division.
I. Prophase: Initiation of Karyokinesis
1. DNA synthesis is complete at this stage
2. Condensation of chromosome
3. Chromosome has 2 chromatids connected by a centromere
4. Duplicated centrosome migrates to the poles of the nuclear membrane
5. Centrosome releases microtubules forming aster. The microtubules reach centromere of each chromosome by forming spindle fibers
6. The disintegration of nuclear membrane initiates at the end of the prophase
7. The cell organelles start to disappear
II. Metaphase: Chromosomal Alignment
1. Nuclear membrane disintegration initiates the stage of metaphase
2. Chromosome becomes distinct with sister chromatids held together by centromere
3. The centromere surface has kinetochores. Kinetochores are binding region for the spindle fibers and are disc shaped
4. Spindle fibers align the chromosomes at the equator of the cell called metaphase plate
5. The chromosome is now arranged equatorially in the cytoplasm attached by spindle fibers
III. Anaphase: Sister Cell is Formed
1. The third stage of mitosis carries one half of chromosome to respective poles
2. Centromere drags the chromatids to opposite poles
IV. Telophase: Separation of Daughter Cells
1. Chromatids groups at the poles of the cell
2. Nuclear membrane is generated around the chromatids
3. Chromatids decondense to become chromatin reticulum
4. Reappearance of lost cell organelles – Golgi apparatus, Endoplasmic reticulum, etc.,
V. Cytokinesis
1. The process of division of one cell into two daughter cells after mitosis is cytokinesis
2. A cell plate is formed in between nucleus
3. The cell plate formation begins with small furrow in between 2 daughter nuclei
4. The furrow extends further to the lateral sides and the cells separate from each other
5. Cell plate is formed by the Golgi Body vesicles namely phragmoplast.
6. The orientation of nuclei is controlled by actin, myosin II and regulatory proteins forming a contractile ring
7. Cell division is accomplished by expansion in size of daughter cells
8. The new plasma membrane is formed by the fusion of intracellular vesicles
The cell division or the cell formation phase takes place at the region of meristems in the plant.
B. Cell Enlargement
Enlargement of cell is the maturation phase where cell size increases to acquire nutrient for the coordinated growth.
The enlargement takes place horizontally where the inner cell wall has high solute content increasing the osmotic pressure for the water to enter.
The entry of water is stored in the vacuolated cells, which increase in size.
High water quantity makes the cell diluted and turgid.
The cell wall now becomes thin. Golgi apparatus has a clear role in the formation of the pressure inside the cell.
This function is also regulated by the hormonal influences of the body along with cytoskeleton.
C. Cell Differentiation
In this phase the cell completely matures and retains stem cell for dedifferentiation.
The phase provides a clear distinction between permanent tissue and meristematic tissues.
Growth Curve
The sigmoid curve representing the rate of growth is the growth curve. The overall growth of the plant is simply represented in the curve.
Four phases of curve are plotted. Namely: Lag Phase, Log Phase, Diminishing Phase and Stationary Phase.
1. Lag Phase: the initial growth period is referred as lag phase. In this phase each cell starts to divide continuously and make itself easily available to uptake of nutrients and increase cell mass. The phase involves gradual increase in cell growth.
2. Log Phase: the rapid cell growth period is the log phase. Under Favorable environmental condition the cell growth increases exponentially in large scale by the multiplication of cell division. Simultaneous nutrient input and maturation takes place in this stage. However, the cell division exceeds the maturation
3. Diminishing Phase: the cells start maturation providing a higher yield of cellular metabolites. The growth or new cell formation is confined to certain region of meristems which divides but to keep up with overall plant growth. Reduces the rate of formation of new cells
4. Stationary Phase: A final stage of plant growth where the meristematic regions constantly produce new cells and old cells are removed. This constant maintenance of cell cycle is the Stationary Phase.
Phases of Growth Citations
- Linear growth retardation in relation to the three phases of growth. Eur J Clin Nutr . 1994 Feb;48 Suppl 1:S25-43; discussion S43-4.
- The diagnostic performance of dental maturity for identification of the circumpubertal growth phases: a meta-analysis. Prog Orthod . 2013 May 23;14:8.
- The influence of growth patterns on sexual size monomorphism in lemurs. J Evol Biol . 2015 Sep;28(9):1670-81.
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Plant Growth: Definition, Types, Examples I Research...
Continue ReadingWhat is Plant Growth?
Plant Growth – An irreversible, progressive increase of an organism’s mass over a period of time governed by the synchronous enlargement of basic unit of life – cell.
Every change starts from the smallest part of our body – our cell. Life started from it and gradually progressed to the present-day beings.
The change of one small amino acid which determined the survival whole living organisms on the earth.
The change was supported by an element of GROWTH. Growth is predetermined in the genetic material and are well regulated by complex array of organ system and environmental interaction in higher organisms.
Though plants evolved alongside the animals with more similar metabolic pathways, physiological functions, structural integrity etc.,
The evolution of two kingdom had a set distinct survival strategy which make them unique and well distinguished from each other.
Characteristics of Plant Growth
1. Plants have an open form of growth. These multicellular organism exhibits unlimited growth.
2. New set of features arises frequently to replace the old ones thereby increasing size, girth and survival of the plant.
3. The unlimited growth is supported by the meristems – growing regions of a plant which produces stem cells for unstopping cell proliferation.
4. As growth proceeds, the length of the plant and the girth of the trunk corresponds accordingly to support the whole plant.
5. The plant growth can be plotted in graph against time – this forms the growth curve.
6. Cells are the basic unit of growth that takes place in 3 phases: Cell division phase, cell enlargement phase and differentiation phase.
7. Differentiation, dedifferentiation and redifferentiation are 3 main characteristic feature of cell
8. Dedifferentiation is main character of plant growth. Differentiation is a process where a cell attains a specific role and becomes a mature cell and does not divide. But plants have the process of dedifferentiation where the mature cell gain to differentiate again for cell proliferation
9. Plant growth depends upon various external factors, namely: Light, Temperature, gravity, water and touch.
10. Growth has a regulator which is fixed in the genetic material
11. The plant growth is plastic and are completely determined by the external cues.
Type of Plant Growth
Plant growth can be categorized into many types, such as:
I. Primary and secondary growth:
Primary growth is cell division of apex of root and stem and secondary growth increases the girth of the tree.
II. Limited and Unlimited growth:
When a region of plant stops growing after particular set of cell division. the growth expressed here is limited growth.
For Example: Flower, leaf, fruit.
The root system and the shoots depend only on unlimited supply of cells through cell division this forms the region to be termed with Unlimited Growth.
III. Vegetative and Reproductive growth:
Cell division and production of stem, leaf, branches without flower can be termed as vegetative Growth. Reproductive growth is a type where the plant produces the flowering part the temporary reproductive part for plant.
Plant Growth Curve
The rate of growth is determined by plotting growth against time. The curved obtained is the Sigmoid curve. The sigmoid curve represents 4 phases.
1. Lag Phase: is the initial phase where the cell proliferation starts at a slow and steady phase of growth
2. Log Phase: exponential phase where the cell proliferation takes place rapidly
3. Diminishing Phase: the rate of growth again reduces
4. Stationary Phase: a steady state of growth over time takes place
Phases of Plant Growth
Cell, division, Cell Enlargement and Cell Differentiation are the 3 phases of Plant growth.
I. Cell division: is the process where the stem cell divides into two where one half retains the ability to proliferate later (i.e.) retaining the ability of stem cell. The others half continue to proliferate.
II. Cell enlargement: The divided cell now elongates horizontally by stretching and becomes rigid. The Cell Division and Cell Enlargement are increasing the size of the cells.
III. Cell Differentiation: 3rd stage is the mature stage where the cell loses its capacity to divide further. This phase is irreversible. But the plant cells have the special ability to dedifferentiate cells for future cell division when needed.
The process of dedifferentiated cell to produce new cells through cell division is redifferentiation.
Plant Growth Hormones
Apart from all the factors said above, plant Hormones also plays a very important role in regulating growth. Hormones Such as:
1. Auxins
2. Gibberellins
3. Cytokinins
Functions of Growth hormones are:
1. They aid in cell division
2. Growth promoters for fruiting and flowerings,
3. Enlargement of cells
4. Germination of seed and formation of root.
Not only hormones certain inhibitors are present to inhibit restrictions at certain sites.
The inhibitors are:
1. Ethylene
2. Abscisic acid. Which induces seed dormancy and senescence of the organism.
Meristem
Meristems are regions of stem cell which shows unstoppable growth over the lifetime of a plant.
The main mechanism of cell proliferation is that a group of cells get differentiated from their stem cells by cell division.
One half of the cell retains the capacity of stem cell and other half gets differentiated. The differentiated cells divide continuously till their threshold and then becomes a matured cell.
In young plants all the region were stem cells, later when the plants mature the regions of cell division becomes restricted slowly and are found in localized area of an adult plant.
Types of Meristems
Meristem is present in both shoot and root have similar functions. Different parts of meristems are:
1. Apical Meristem: present in the tips of root and shoot. This meristem is only responsible for primary growth.
2. Lateral Meristem: Present laterally to the plants are responsible for the girth of the tree Example: Vascular Cambium, Cork Cambium
3. Intercalary Meristem: present in between mature cells
Further, the meristems can also be classified as DETERMINATE and IN – DETERMINATE. Determinates are cells whose fate is already determined who lives for short period of time like Bud, leaves etc., Indeterminates are the cell who does not lose his identity throughout their life.
Plant Growth Citations
- Radial plant growth. Curr Biol . 2017 Sep 11;27(17):R878-R882.
- Cytokinin signaling in plant development. Development . 2018 Feb 27;145(4):dev149344.
- The Phloem as a Mediator of Plant Growth Plasticity. Curr Biol . 2019 Mar 4;29(5):R173-R181.
- Molecular Aspects of Plant Growth Promotion and Protection by Bacillus subtilis. Mol Plant Microbe Interact . 2021 Jan;34(1):15-25.
- Plant Growth Promoting and Biocontrol Activity of Streptomyces spp. as Endophytes. Int J Mol Sci . 2018 Mar 22;19(4):952.
- Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture. World J Microbiol Biotechnol . 2012 Apr;28(4):1327-50.
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