Category: Biology
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Isomer: Definition, Types, & Examples
Continue ReadingIsomer Definition
Isomer comprise 2 molecules that differ in terms of their structure but are represented by the same molecular formula. The number of atoms would be the same for these isomers but their arrangement would differ due to which they would exhibit different physical properties even though they have the same molecular formula.
The functional groups associated with each molecule may differ which alters their properties. The molecules can be converted into their respective isomers by the process of isomerization. This may be spontaneous or not.
Types of Isomer
Isomers are classified into 2 types stereoisomers and structural isomers.
i. Structural Isomers
These molecules differ in respect to the functional groups and the specific attachment and arrangement of atoms. All the different isomers will have different IUPAC names and as they comprise different functional groups they may be classified into different groups.
They are of different types including position isomers that differ in accordance to the position of the functional group, chain isomers that differ in regard to their branching patterns, skeletal isomers that have different carbon chains, and functional groups isomers.
Tautomer is a kind of structural isomer that undergoes spontaneous interconversions between the different isomers. It will exhibit different properties based on the isomer conformation it exists in. Some of these spontaneous conversions are so rapid that it is difficult to isolate the different forms.
ii. Stereoisomers
These isomers will have identical bond structures but the geometric positions of atoms and functional groups will differ. Different types of stereoisomers include diastereomers, conformational isomers, and enantiomers.
Enantiomers are non-superimposable mirror images that comprise chiral centers. Diastereomers may or not consist of chiral centers and are not mirror images of each other. Conformational isomers showcase different rotations around single bonds.
Isomer Examples
Methoxyethane and Propanol: The C3H8O chemical structure has many isomers like methoxyethane isomers and propanol isomers. The propan-2-ol and propan-1-ol comprise the propanol isomers that differ in regard to the position of an oxygen atom that is either present on the central carbon atom or the terminal carbon respectively.
In the methoxyethane isomer, the oxygen atom is placed on the center instead of being linked to a single carbon atom, and due to which it is ether.
Methylacetylene and Allene: These comprise C3H4 isomers that differ in the kind of bonding shown by them. Allene shows 2 double bonds between the carbons, whereas methylacetylene has only one single bond and one triple bond.
Fulminate and Cyanate: They constitute isomers of CNO. In the case of fulminate, the N atom is linked to both the O and C atoms. While in cyanate, both N and O are linked to the central C atom.
Glucose and Fructose: They are the most common examples and are C6H12O6 isomers. They differ in regard to the placement of a double-bonded O atom. The O is positioned on the first C in glucose, while in fructose it will be located on the second C in fructose.
Importance of Isomer
Isomers are significant in the case of pharmaceuticals, as generally one isomer of a compound will exhibit the desired reaction or effect. For example, ibuprofen will target the binding site and bind to it generating relief from pain in only one isomer form.
Another example is cisplatin that comprises an anticancer drug, while transplatin that is its isomer shows no anti-cancer traits. One isoform of thalidomide was used to treat morning sickness in pregnant women in the 1950s, but its stereoisomer acted as a teratogen causing birth defects in children.
In the human body, these isomers are critical for enzyme function. The structure of an enzyme including its functional group, orientation, and bond length is vital to its functioning as they bind very specifically to the active site of an enzyme.
The isomers of enzymes that vary in their structure won’t be able to bind to the active site. For example, the isomer of the enzyme triose phosphate isomerase is not able to catalyze the interconversion of dihydroxyacetone and (R)-glyceraldehyde phosphate.
Isomer Citations
- Single-isomer drugs: true therapeutic advances. Clin Pharmacokinet . 2004;43(5):279-85.
- Pentanol isomer synthesis in engineered microorganisms. Appl Microbiol Biotechnol . 2010 Jan;85(4):893-9.
- Single isomer cyclodextrins as chiral selectors in capillary electrophoresis. J Chromatogr A . 2020 Sep 13;1627:461375.Â
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Barr Body: Definition, Types, & Examples
Continue ReadingBarr Body Definition
Barr Body is also referred to as sex chromatin and represents the inactivated X chromosome present in the somatic cells of females. Females have 2 X chromosomes in their sex chromosome constitution, while males have one Y and X chromosome each.
What is Barr Body?
In the somatic cells of females, one X-chromosome is inactivated randomly by the lyonization process resulting in the formation of a Barr body. This occurs for dosage compensation as females have 2 X chromosomes which would otherwise produce double the amount of gene products compared with males.
In all organisms where the sex determination is by XY chromosomal method, this process of X-chromosome inactivation can be observed. This process helps in balancing the X chromosome expression in males and females.
The Barr body occurs as a result of heterochromatinization, while the active X chromosome is observed in a euchromatin state. The inactivated DNA is condensed and packed to repress the genes such that their transcription is hindered. While in the active X chromosome it is not packaged to freely allow molecules involved in transcription to interact with it.
Which X Chromosome becomes the Barr Body?
The selection of the X chromosome that has to be inactivated is done by a random process in the embryonic stage of any particular cell and it stays in this state for the rest of its life. The cells resulting from the division of these cells will all have the same X-chromosome inactivated. The number of Barr bodies is given as one less than the number of X-chromosomes present.
For instance in Turner’s syndrome, no inactivation of the X chromosome would occur even though the individual is female and in Klinefelter’s syndrome, one of the X chromosomes would be inactivated and would be present as a Barr body.
Mechanism of X-inactivation and Barr Body
Two genes Tsix (Xist reversed) and Xist (X-inactive specific transcript) are found in the X-inactivation center (XIC) that is located near the centromere on the X chromosomes. Xist is responsible for the inactivation of a gene and Tisx represses Xist. The chromosome that produces more expression of the Tsix gene will have less probability of being inactivated.
Initially, both X chromosomes in the female somatic cell express equal levels of Xist RNA, but once the process of inactivation starts the chromosome to be inactivated will express more Xist RNA that will then coat the whole chromosome and silence it. The presence of Tsix in other chromosomes represses the expression of the Xist gene that maintains it in the active form.
Not all the genes of the inactivated X chromosome are silenced. The Xist gene along with some other genes escapes heterochromatinization. So, a female that has Turner’s syndrome will still express fewer genes than a normal female.
Genetic Disorder of Barr Body
In the case of individuals with Turner’s syndrome that only has one X-chromosome, the individual may survive even though they don’t have a Barr body and express lesser genes. They won’t be able to develop like a normal average. Chromosomal abnormalities where there are more than 2 X chromosomes in an individual can lead to developmental dysfunctions.
In normal females, random inactivation can cause the maternal chromosomes to be silenced half the time, and the paternal one in the other half. But if one of them is repressed more than the other then depending on their ratio this may result in some problems.
Barr Body Citations
- Significance of the Barr body in human female tumors. Cancer Genet Cytogenet . 1981 Nov;4(3):269-74.
- The disappearing Barr body in breast and ovarian cancers. Nat Rev Cancer . 2007 Aug;7(8):628-33.
- Deciphering the Role of the Barr Body in Malignancy: An insight into head and neck cancer. Sultan Qaboos Univ Med J . 2017 Nov;17(4):e389-e397.
- Images are created with BioRender.com
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Neurogenesis: Definition, Types, & Examples
Continue ReadingNeurogenesis Definition
Neurogenesis refers to the generation of new neurons. These neurons arise from stem cells or progenitor cells during embryonic and early development, it can continue into adulthood in organisms like fishes, amphibia, and insects. The adult mammalian nervous tissue was thought to be incapable of this process, but recent research findings prove this as not true.
Is Neurogenesis True?
Even in adults many tissues could regenerate or replicate themselves, in event of growth or repair, but it was thought that this was not the case for neurons. One of the reasons behind this was the complexity of the structure of neurons; they have cell bodies from which one long axon emerges and there are also dendrites that are highly branched that rise from these cell bodies.
This nerve cell is part of a networking functioning unit that makes its replication a difficult process. Another reason is that damage to the brain or spinal cord causes irreversible damage hinting that there is a lack of neuronal regeneration. Death of neurons with aging showed symptoms of cognitive decline as these cells are not being replaced.
Lab Studies of Neurogenesis
Research lab studies on organisms like shrews and rats demonstrate the significance of neurogenesis. New labeling and imaging techniques aided in proving the fact that new neurons were born also in the adult brain. Environmental processes played a key role to alter neuronal degeneration with age.
Exercises and cognitive processes strengthen and enhance neurogenesis while stress impacted this process negatively. It was discovered in 2005, that older mice who were still active on wheels showed a higher rate of neurogenesis than sedentary mice.
Neurogenesis in Adults
Research on adult hippocampal neurogenesis has revealed significant data on this process. Neuronal regeneration occurs in 2 regions of the adult mammalian brain; one of them is the hippocampus.
This center of memory is found deep in the brain and has a tiny sea horse shape and helps in the processing of short-term memory into long-term memory. It also helps with spatial learning and navigational ability.
The other region is the subventricular zone where neurogenesis can be seen. This region comprises stem cells and progenitor cells. More research is needed to understand what happens to the new neurons formed here.
Some of them migrate to the olfactory bulb, but there is major purpose is still to be discovered. The presence of these progenitor cell-enriched sites may make it easier for neuron generation.
Neurogenesis and Hippocampus
The hippocampus region is susceptible in the early stages of Alzheimer’s disease, which may damage the area and also affect the disease’s progression. Hippocampus is critical for navigation and memory and possible damage may impact their functioning as in Alzheimer’s patients that get lost easily and find it hard to remember things. Besides neurodegenerative diseases, hypoxic conditions may also damage this region.
Such conditions of low oxygen availability can occur during a heart attack, carbon monoxide poisoning, sleep apnea, and other dangerous situations like drowning. Impairment of this region can also cause anterograde amnesia, where the person struggles with making new memories.
How to Enhance Neurogenesis?
Recent research has indicated that neurogenesis does occur in the adult brain. The factors that can potentially increase this process are being investigated. Exercise, sex, intermittent fasting, and learning can increase the neurogenesis rate.
Foods like blueberries and dark chocolate that are rich in flavonoids, omega-3-fatty acids found in fishes like salmon, and resveratrol found in red wine can also enhance this process. Some factors can also decrease neurogenesis like sleep deprivation, stress, alcohol, and diet high in saturated fat.
Thus up to a limit changes in behavior and diet can enhance the rate of neurogenesis. Further research needs to be done to come up with a therapeutic technique for reversing hippocampal damage and damage caused by aging.
Neurogenesis Citations
- Adult Hippocampal Neurogenesis: A Coming-of-Age Story. J Neurosci . 2018 Dec 5;38(49):10401-10410.
- Nutritional Factors Affecting Adult Neurogenesis and Cognitive Function. Adv Nutr . 2017 Nov 15;8(6):804-811.
- Adult neurogenesis: beyond learning and memory. Annu Rev Psychol . 2015 Jan 3;66:53-81.
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Phylum Chordata: Definition, Characteristics, & Examples
Continue ReadingPhylum Chordata Definition
Chordate belong to the phylum Chordata that comes under the Deuterostomes kingdom that is characterized by the development of the anus that precedes the development of the mouth in the embryonic stage.
Chordata phylum comprises a large variety of organisms including invertebrates that lack a backbone and vertebrates that possess a backbone. This phylum includes 3 subphyla that are Urochordata, Cephalochordate, and Vertebrata. They generally have a bilaterally symmetrical shape though exceptions are there.
Phylum Chordata Characteristics
The following characteristics are exhibited by all the organisms that come under this phylum at some stage of their lives or during embryonic development.
Pharyngeal Slit: This can also be seen in invertebrates where they function in filter-feeding. Whereas in vertebrate fishes they develop into gill arches the function that supports gills. In other vertebrates like humans, these gill slits can only be seen in the embryonic stage and disappear later in development. This tissue may develop into eustachian tubes or jaws in terrestrial vertebrates.
Dorsal Hollow Nerve Cord: This dorsal hollow tube comprises nerve fibers that will develop into the CNS that consists of the brain and spinal cord. The vertebral column shields this nerve cord. The vertebral column consists of bones that form our backbone. Whereas in non-chordates the nerve cords are located either laterally or ventrally and are solid.
Notochord: This skeletal flexible rod is made of cartilage and functions to support the structural frame of the organism. It is present between the nerve cord and the digestive tube. The phylum derives its name from this rod. In vertebrates, it is the precursor of the spine or backbone.
Post-Anal Tail: This posterior elongation provides balance, helps the aquatic organisms in propelling themselves in water, and is utilized by certain terrestrial vertebrates in signaling or in finding a mate. This tail disintegrates as it shrinks and can be seen as a tailbone during embryonic development in apes and humans.
Chordata Subphylum
Vertebrata: This subphylum is also known as Craniata as the comprising organisms have a cranium case that protects their head and is known as a skull. They are also distinguished by the presence of a closed circulatory system, unique motor and sensory cranial nerves, internal organs, and a highly evolved brain. This subphylum includes amphibians, fish, mammals, reptiles, and birds. Their evolution can be studied using paleontological pieces of evidence like fossils as due to the presence of cartilage and bone, their remains were preserved.
Cephalochordata: Also called lancelets this subphylum comprises marine filter-feeding organisms. These have segmented small elongated and soft bodies due to which they did not fossilize well. They bury themselves in substrates and are seen in soft bottoms with exposed head regions consisting of tentacles that help in capturing the prey. Though they resemble fish, they do not have a brain, limbs, scales, and backbone like them. They have a greater number of pharyngeal slits than the fish.
Urochordata: This sub-phylum is also referred to as Tunicates and comprises sea salps and squirts. They are also soft-bodied organisms and thus their fossils are rare. These marine organisms are barrel-shaped filter feeders that are not segmented. The tail can be seen in the larval stage when it is free-living. But in adults, they lose the tail and attach to a substrate. In adults, the only chordate characteristic visible is the pharyngeal slits.
Phylum Chordata Examples
Lampreys: Belonging to subphylum vertebrates this chordate is a filter feeder during its larval stage. The adult of this jawless fish is a parasite that latches on to other fish with its oral disk that comprises teeth. They are not obligate parasites and the adults may live off the reserve they built in the larval stage. The adult exhibits external gills, nerve cord, cartilaginous skeleton, and a notochord. In the larval stage, they utilize a mucus-secreting organ that helps to trap the food in their pharynx and also show a post-anal tail.
Sea Squirts: This barrel-shaped organism belongs to the subphylum Tunicates. The larval stage resembles a tadpole and has a dorsal nerve, post-anal tail, notochord, and pharyngeal slits. In their adult stage, they are primarily filter feeders that have 2 siphons that are openings that are employed to draw water during filter feeding. They acquire their food phytoplankton by this method and drain the excess water through the other siphon.
Phylum Chordata Citations
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Sexual Reproduction: Definition, Types, & Examples
Continue ReadingSexual Reproduction Definition
Sexual Reproduction defines the process through which organisms produce progeny that has variations as a result of the recombination process involved in gamete formation. Two individuals of different sexes contribute as parents, create new offspring by combining their genetic information.
This genetic information is present within the chromosomes that are present in the organelle nucleus of sex cells known as gametes. The gametes produced by the male are known as sperm while those produced by the female are known as egg or ovum.
During the process of sexual reproduction, the syngamy of these gametes leads to the production of a zygote that later develops into an embryo. This embryo has half its genomic content from one parent and the other half from the other.
For instance, in the case of humans, 46 chromosomes are present in an individual out of which 23 are from its father and the other 23 from its mother. The result is an organism that is not a clone of either of its parents but resembles both of them.
Sexual Reproduction and Fertilization
During this process, traits are passed down to the progeny. These traits include phenotypic traits that are required for adapting to their environment and thus directly influence their survival and genotypic traits like resistance etc. The genes responsible for these traits undergo selective pressures according to the environment they live in.
This evolutionary process of natural selection helps in the survival of individuals with favorable traits and these then reproduce. Sexual reproduction aids in increasing diversity or variation that works as the raw material for different evolutionary processes like natural selection. It differs remarkedly from asexual reproduction where only one parent is involved.
There is no syngamy in asexual reproduction and as a result, the offspring are the exact clones of their parent. This kind of reproduction can be seen in certain organisms like fungi, bacteria, corals, starfish, hydras, and plants like strawberries.
Types of Sexual Reproduction
i. Allogamy
Allogamy refers to the syngamy where the involved gametes are from 2 different individuals. Ovum or egg is the female gamete while sperm is the male gamete. These are specialized sex cells that are structured in a manner that enhances fertilization probability.
These cells are haploid and consist of 23 chromosomes in humans. When they fuse they form a diploid zygote that then undergoes mitosis to form an embryo. Mitosis is a type of cell division seen in cells after they have successfully replicated their DNA.
Animals have courtship rituals that help them to breed with an organism that will reproduce to produce fertile progeny that has genes that increase their fitness and survivability. The desirable traits include aggression, speed, good health, agility, etc.
As a result of sexual reproduction, phenotypic and genotypic variations can be seen. Based on these variations, the organisms choose their mate that exhibits the desirable phenotypic traits. These variations also increase competition as a result only the best animal that shows desirable traits are chosen and this is known as sexual selection.
This also leads to sexual dimorphism, wherein different sexes are distinct morphologically. The males are generally brightly colored and often have exaggerated body parts that help them to attract a mate. Whereas the females are camouflaged with dull colors as they are primary caretakers of their offspring.
But often these sexually selected traits may also affect the survivability of a species. For instance, bright coloration not only attracts potential mates but also predators. But these traits do persist in populations where mating is essential.
a. Internal Fertilization
This occurs within one of the parent’s bodies, where the gametes meet and fuse often via sexual intercourse. It generally happens in the female body, but rarely this can also be observed in the case of seahorses. In seahorse, the female will implant her gametes into the male where the fusion will occur. The further steps of this process are species-specific.
In some organisms like reptiles, insects, and birds, they may lay fertilized eggs, wherein the rest of development occurs. These eggs also contain yolk that helps to nourish the embryo. After a certain period, the developed young ones will hatch. This is referred to as oviparity. In the case of mammalian species, the embryo grows inside the body of their mother, and the baby is born live and this is known as viviparity.
In placental mammals the embryos are supported by the placenta, which helps to provide the embryo with nutrition, is also involved in thermoregulation, and also removes the waste products. While in marsupial offspring like a koala is removed from inside the mother’s body after completing a brief gestation period.
They then complete their development in an external pouch present in front of their mother’s body. Ovoviviparity represents a third type of development whereby the embryos grow and develop in eggs within the parent’s body and ultimately hatch inside and thus giving the appearance of live birth.
b. External Fertilization
Here the syngamy or fusion of gametes occurs outside the body of the parents. Most invertebrates, amphibians, and fish employ this method, where a large number of gametes are released synchronously in proximity from both the parents.
This quick release of the gametes into an aquatic medium is referred to as spawning. The females can also lay an egg on a substrate where the males will also release their gametes. These gametes have specialized adaptations for movement like the presence of strong flagella.
ii. Autogamy
Here the female and male gametes that fuse are produced by a single individual. These species that can produce gametes of both sexes are known as hermaphrodites. It is similar to asexual reproduction, in the aspect that only 1 parent is involved, but unlike asexual reproduction the progeny produced have variations resulting from the recombination of chromosomes from the male and female gametes. Animals that reproduce by allogamy include earthworms and plants. Reproduction between hermaphrodites is possible and can in this case increase genetic diversity.
Advantages of Sexual Reproduction
Mitosis can result in accumulation of some harmful deleterious mutations over time. Sexual reproduction only allows a fraction of these harmful genes to be passed in the progeny unlike asexual reproduction. This leads to an increase in fitness that also increases their survivability.
This is further increased by natural selection, that eventually eliminates these genes from the population. More genetic variations helps to increase the adaptability of an organism to its environment through selection. Some mutations that are of no present use may prove beneficial in the future circumstances. This also acts as the driving force for speciation.
Sexual Reproduction Citations
- Thyroid hormones and female reproduction. Biol Reprod . 2018 Nov 1;99(5):907-921.
- Bisphenols in the pathology of reproduction. Ceska Gynekol . Winter 2019;84(2):161-165.
- Role of oxidative stress in female reproduction. Reprod Biol Endocrinol . 2005 Jul 14;3:28.
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Heterochromatin: Definition, Types, & Examples
Continue ReadingHeterochromatin Definition
Heterochromatin is the densely packed region of chromatin that impairs the transcription of that particular section of DNA. Euchromatin unlike heterochromatin is lightly packed and genes that are actively transcribed are located in this region.
Chromatin comprises DNA and proteins that bind DNA and stabilize it and it is located in the nucleus in the case of eukaryotes. In its condensed state heterochromatin restricts RNA and DNA polymerases to access the DNA strand and thus, it inhibits both DNA transcription and replication. Heterochromatin is of 2 types facultative and constructive heterochromatin. Heterochromatin constitutes only less than 10% of chromatin in humans.
Heterochromatin Structure
The DNA is present as chromatin that is the complex of proteins and DNA in eukaryotes. The proteins involved in this complex are known as histones that wrap the DNA around them. Approximately 200 bp DNA is wrapped around each histone to form nucleosomes which are sets of 8 histones.
Histones present in nucleosomes are H23, H2A, H4, and H3. Their 2 copies each are present in the nucleosome that form an octamer. Nucleosomes are connected by linker DNA that is strands of DNA connecting both nucleosomes.
This structure of chromatin that is loosely packed is referred to as the beads-on-string model. The beads represent nucleosomes and the string denotes DNA. It depicts how the nucleosomes are connected by DNA comprising chromatin.
Heterochromatin represents the second level of packaging of DNA into a 30-nm condensed fiber that is helically coiled and whose diameter measures 30nm. This type of heterochromatin is more easily visible in G-banding as it is a more tightly condensed form.
The 30 nm fiber structure can be further compacted and condensed into chromosomes and further condensation leads to the formation of metaphase chromosomes.
A double-strand DNA helix is wrapped around an octamer of histones that form nucleosomes to constitute beads on the string structure of euchromatin. It can be further compacted into heterochromatin that comprises 30 nm fiber. Finally, this can be compacted into chromosomes and metaphase chromosomes.
DNA is in the heterochromatin conformation when it is transcriptionally repressed was the polymerases and other regulatory proteins cannot bind to it in this conformation. The linker DNA in euchromatin is available for transcription, while in heterochromatin conformation it is coiled around nucleosomes and is not exposed.
Heterochromatin Types
There are two Types of Heterochromatin: Constitutive and Facultative
Besides the 2 major types of heterochromatin, there are other kinds that intermediate features of facultative and constitutive heterochromatin.
Constitutive heterochromatin stays in heterochromatin configuration and is more stable and often comprises repeated DNA sequences known as satellite DNA. For instance, this kind of heterochromatin is present in telomeres and centromeres that have structural roles.
Facultative heterochromatin is reversible and can change its structure based on the cell cycle stage. It also consists of repeated sequences of DNA called LINE sequences. For example, the Barr body is the inactivated X chromosomes.
Heterochromatin, Cell Cycle, and Gene Expression
DNA packaging level correlates with cell cycle stages. DNA exists in euchromatin form when it either needs to be transcribed or replicated. When the genes in the DNA do not need to be transcribed or replicated then it exists in heterochromatin conformation.
DNA exists in transcriptionally active forms during the interphase stage, while it is present in metaphase chromosome form in mitosis or meiosis stage when the cell is dividing. Thus by regulating DNA conformation or packaging, gene expression can be controlled.
Housekeeping genes are usually present in the euchromatin region as they need to be constitutively expressed as they are involved in metabolic reactions that sustain the cell. The genes that are not actively expressed occur in heterochromatin configuration. This type of gene regulation is achieved by histone tail modifications.
Acetylation or methylation of histone tails can determine the state the DNA exists in. For example, hypoacetylation on the histone tail will repress DNA expression and change the conformation to heterochromatin.
Heterochromatin Citations
- Role of H3K9me3 heterochromatin in cell identity establishment and maintenance. Curr Opin Genet Dev . 2019 Apr;55:1-10.
- Establishment and evolution of heterochromatin. Ann N Y Acad Sci . 2020 Sep;1476(1):59-77.
- Ten principles of heterochromatin formation and function. Nat Rev Mol Cell Biol . 2018 Apr;19(4):229-244.
- Image are created with BioRender.com
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Turgid: Definition, Types, & Examples
Continue ReadingTurgid Definition
Turgid refers to cell states where they are swollen due to uptake of water. Different tissue types or cell types can become turgid. Animal cells may lyse or split if they become too turgid. Other cells that usually exist often in turgid states have an extracellular matrix of fibrous tissue that can help maintain the integrity of the cells as in animals cells.
For instance, Connective tissues like cartilage comprise proteoglycan molecules that consist of sugar and protein mixtures that also link adjacent cells. This extracellular matrix helps them to maintain their integral structure even when facing external pressure and also supports them.
What is Turgid?
Plant cells due to the presence of large vacuoles in their cytoplasm always exist in turgid conditions. Tonoplast the membrane of this organelle aids in actively moving water and other nutrients into the vacuole for storage. This causes the vacuole to swell which causes pressure on the cell walls of the plant. This pressure is referred to as turgor pressure.
When a cell experiences high turgor pressure it is said to be turgid. This pressure is exerted on the cellulose molecules comprising the cell wall. Cellulose are strong fibers that create a cell wall by tightly wounding around each other.
Plants become rigid when turgid tissue walls push against each other. This rigidity in plants helps them to keep their posture and stand up straight. While in the case of animals they only need turgid cells for performing specialized functions. Plants can regulate the movement of leaves and stems by controlling the turgor pressure of those sites.
Such instances include, for absorption of maximum sunlight the turgor pressure may be lowered in some cells to move the particular part towards sunlight. Besides plants, fungi and bacteria also possess cell walls in their structure. In fungi their purpose is similar to plants i.e., to maintain their integrity.
While bacterial cells employ cell walls to prevent lysis or rupturing of their cells in event of excess turgor pressure. They manipulate water potential with the help of turgor pressure and thus regulate the movement of water.
As they are unicellular beings they do not require cell walls to support multi-cellular structures. Turgidity can be observed in animal cells when their surrounding is hypotonic when compared with their cell contents. This indicates that the solute concentration is less in surroundings so following the concentration gradient the water will flow to the cell leading to its intake.
To prevent being turgid the cells would require to pump water out actively. If the cell is not able to remove water more quickly than it enters the cell, then the cell may become too turgid and rupture. But if the plant cells are placed experimentally in a similar situation they will not lyse due to the presence of cell walls.
Turgid Citations
Reduction in turgid water volume in jack pine, white spruce and black spruce in response to drought and paclobutrazol. Tree Physiol . 2000 May;20(10):701-707.Â
The effect of plant growth regulator treatments on the levels of ethylene emanating from excised turgid and wilted wheat leaves. Planta . 1980 Apr;148(4):381-8.
Differential requirement for NO during ABA-induced stomatal closure in turgid and wilted leaves. Plant Cell Environ . 2009 Jan;32(1):46-57.
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Oviparous: Definition, Types, & Examples
Continue ReadingOviparous Definition
Oviparous term is used to describe egg-laying animals, where the young hatch from the eggs that have been expelled from the body. Fertilization in oviparous animals can be external or internal, but the young hatch outside of their body.
Oviparous animals include birds, amphibians, reptiles, and fish. While in animals like snakes and sharks, ovoviviparity is seen where the young hatch from eggs inside the female body itself.
What is Oviparous?
Oviparous comprises an evolutionary strategy where eggs are produced by females. Eggs are the gamete contributed by the females. The males supply their genetic material in form of sperm that must find and fertilize the egg. The egg on fertilization after many cleavages and divisions form an embryo.
Most of the oviparous organisms produce many fragile small eggs, while others will produce few large hard eggs. Both of these strategies are advantageous to organisms. If a large number of eggs are produced, then a large number of offspring can overcome predators.
Whereas, larger eggs that are strong, help in their survival and development till birth, then after hatching is able to escape from predators. But there are disadvantages of this reproductive strategy.
Oviparous animals must protect the eggs by hiding them well before they hatch as they do not carry their developing embryos like ovoviviparous and viviparous animals.
They also must warm the eggs by sitting on them, till they hatch, for instance, penguins often sit on their eggs constantly to warm them. The eggs are vulnerable to predator attacks.
Oviparous Examples
Oviparous Birds: Chickens are an example of oviparous birds that releases an egg from one of the ovaries that will be laid irrespective of whether it is fertilized or unfertilized. If it is fertilized then the embryo develops by feeding on the nutrition-rich yolk present in the egg. Once the young are developed it hatches and is now capable of feeding and walking. Generally, all birds are considered oviparous and lay internally fertilized eggs that have a hard shell. The young produced are precocial and can walk and feed on hatching
Oviparous Reptiles: Reptiles are also oviparous and their reproductive strategy is similar to birds, the difference occurs in the shells of their eggs. Reptiles lay eggs that have a softer shell as opposed to birds. These eggs have a leathery texture and are incubated in mounded nests or burrows for warmth and to provide a stable temperature. This mechanism is known as temperature-dependent sex determination.
Oviparous Fish: Fishes also exhibit oviparity as they lay their eggs in a nest where they are fertilized by the sperms that are released in the water by males. The fertilization process is thus external. The sperm swims towards the eggs by chemotaxis. Other various mechanisms may be species-specific that ensures mating in these organisms. Some fishes employ mating dance or moves to release their gametes simultaneously to increase the probability of fertilization.
Oviparous Amphibians: Amphibians also lay their eggs in standing water and are thus oviparous. They also exhibit external fertilization but the eggs hatch at larval stages. The larval stages are equipped with appendages like tail and gills, that facilitate the rest of the development in water. These larvae will develop into an adult by metamorphosis.
Oviparous Citations
Lipids of the eggs and neonates of oviparous and viviparous lizards. Comp Biochem Physiol A Mol Integr Physiol . 2000 Dec;127(4):453-67.
The restricted ovulator chicken strain: an oviparous vertebrate model of reproductive dysfunction caused by a gene defect affecting an oocyte-specific receptor. Anim Reprod Sci . 2012 Dec;136(1-2):1-13.
Incubation temperature induced phenotypic plasticity in oviparous reptiles: Where to next? J Exp Zool A Ecol Integr Physiol . 2018 Jul;329(6-7):343-350.
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Binomial Nomenclature: Definition, Types, & Examples
Continue ReadingBinomial Nomenclature Definition
Binomial Nomenclature system consists of scientifically assigning names to organisms that were developed by Carl Linnaeus. In Systema Naturae, he tried to identify and name different animals and plants and this was published between 1735 and 1758. In this work, he established the concept of binomial nomenclature.
The nomenclature of organisms is done such that it lays clarity on ecology and evolution in general. Having a universally accepted name helps give clarity and identity to the species and promotes discussions even among researchers of different nationalities. It also helps avoid confusion regarding different colloquial local names.
What is Binomial Nomenclature?
Under Binomial Nomenclature system, 2 names or epithets are employed in the scientific name. The first is known as the generic epithet that specifies the genus of the organism. The other epithet is known as a specific epithet that describes the species of the organism. The epithets are derived from Latin base and are assigned based on characteristics of the organism that links it to a specific group.
The scientific name should be italicized or underlined when written to recognize it as a scientific name. In the case of a scientific name, only the generic epithet should be capitalized as opposed to some older documents. If many species of the same genus are discussed together, then the generic name can be abbreviated, otherwise, the full name is usually written.
The generic epithet that denotes the genus name that also represents the taxonomic hierarchy of each organism that shows its relation to other taxonomic groups, evolution, origin, and its life history.
Lower taxonomic ranks have common traits that link them to higher taxonomic groups. Even if the species loses some of its ancestral traits, this naming system helps in understanding those evolutionary relationships in the context of taxonomy. The species may even be sub-divided into smaller sub-species that are then represented after species name, giving more specific details.
It may be useful as species are also even now evolving which creates a requirement for multiple subspecies designation. The scientist who first discovers and describes a species is sometimes noted after the species’ scientific name. This gives some clarity as to the authority and helps to avoid any confusion as any changes in names are documented.
Binomial Nomenclature Examples
Felis concolor: This animal is also known as the puma, mountain lion, cougar, painter, or catamount. This large cat has many different names not only in English but also in Spanish. It is a predatory single-colored cat that is known as poema, yaguá-pitá, león Colorado, guasura, and onça-vermelha.
When sharing any information or research on this animal, scientists need to be clear of the confusion posed by colloquial names. The emergence of the scientific name Felis concolor helps avoid any kind of confusion.
Homo sapiens: This scientific name is combined with 2 Latin words hom and sapien. Hom refers to the humans thus indicating the genus Homo that it belongs to. This genus includes the extinct or ancestors and the modern forms of humans. The specific epithet details the only living species of this genus and also segregates us from other species like Homo neaderthalensis that got extinct as a consequence of competition from modern man.
The skill of the modern man to use tools and increased brain compacity that helped in language formation must have aided in their successful evolution. There is also some evidence that the 2 species may also have interbred at some point.
Binomial Nomenclature Citations
The Importance of Binomial Nomenclature for the Identification of Pollen Aeroallergens. J Allergy Clin Immunol Pract . 2021 Jul;9(7):2642-2644.
Binomial nomenclature for virus species: a long view. Arch Virol . 2020 Dec;165(12):3079-3083.
Binomial nomenclature for virus species: a consultation. Arch Virol . 2020 Feb;165(2):519-525.
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Streptococcus: Definition, Types, & Examples
Continue ReadingStreptococcus Definition
Streptococcus is a type of Gram-positive bacteria consisting coccus shaped structure and occurs in chains of varying lengths. The members of streptococcus cause numerous infections including scarlet fever, tonsillitis, erysipelas, endocarditis, rheumatic fever, glomerulonephritis, impetigo, pneumonia, meningitis, lymphadenitis, and wound infections. It is a genus of bacteria named Streptococcus and the plural is streptococci.
What is Streptococcus?
Streptococcus is a type of gram-positive bacteria that mainly occurs in cocci shape. The bacteria is also known as strep and belongs to the bacterial family Streptococcaceae of the order Lactobacillales. A Viennese surgeon named Albert Theodor Billroth coined the name based on their appearance. The word streptos is a Greek word that means twisting or bending, therefore they are named ‘streptococci.
Generally, most of the bacteria are oxidase-negative, catalase-negative, and facultative anaerobes. Exotoxins are also produced by some pathogenic species of the genus. Several streptococcus species cause numerous infections in humans such as scarlet fever, erysipelas, endocarditis, rheumatic fever, tonsillitis, impetigo, meningitis, pharyngitis, and wound infections.
Anti-phagocytic components such as hyaluronic acid-rich capsule, m protein, toxins are also produced by some of the species. It also produces enzymes such as streptokinase, streptodornase, hyaluronidase, and proteinase. Based on their hemolytic features, the members of Streptococci may be classified as alpha-hemolytic, beta-hemolytic, and gamma-hemolytic.
The bacteria that can oxidize iron in the hemoglobin of RBCs are known as Alpha-hemolytic streptococci. In blood agar, they appear greenish and convert hemoglobin to biliverdin. Beta-hemolytic streptococci can completely lyse the red blood cells. They also complete hemolysis on blood agar such as Streptococcus pyogenes that release streptolysin O and S. The hemolysis cannot be caused by Gamma-hemolytic streptococci.
According to Lancefield grouping, the Beta-hemolytic streptococci may be further classified into various groups including from groups A to V (not including I and J) several strep diseases may cause by group A strep and group B strep, thus they are medically important.
Streptococcus Classification
• Domain- Bacteria
• Phylum – Firmicutes
• Class- Bacilli
• Order- Lactobacillales
• Family- Streptococcaceae
• Genus- Streptococcus
Streptococcus Citations
A visual review of the human pathogen Streptococcus pneumoniae. FEMS Microbiol Rev . 2017 Nov 1;41(6):854-879.
Streptococcus pneumoniae Capsular Polysaccharide. Microbiol Spectr . 2019 Mar;7(2).
Streptococcus pneumoniae: virulence factors and variation. Clin Microbiol Infect . 2010 May;16(5):411-8.
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