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Zygote

...947;ωτόν ) is a cell that is the result of fertilization . That is, two haploid ...e —merge into a single diploid cell called the zygote . Animal zygotes undergo mitotic cell divisions to become an embryo . Other organisms...

Zoology

This article is the top of the Zoology series. History of zoology (before Darwin) History of zoology (since Darwin) ...

Zona pellucida

... pellucida is a glycoprotein matrix surrounding the plasma membrane of a mammalian oocyte . This...e binds spermatozoa , and is required to initiate the acrosome reaction . The zona glycoprotein, ZP3 , is responsible for sperm binding, adhering to ...

Y chromosome

The Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome ). The sex chromosomes are one of the 23 pairs of human chromosomes. The Y chromosome ...

Xylem

...heids and vessel elements In vascular plants , the xylem is the tissue that carries water up the root and stem. In trees , it constitutes wood ; the word is der...

X-ray crystallography

...aphy is a technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded a...

X chromosome

The X chromosome is one of the two sex chromosomes in humans and other animals (the other is the Y chromosome ). It is a part of the XY sex-determination system . Contents showTocToggle("sh...

Astrobiology

...speculative field within biology which considers the possible variety of extraterrestrial life . It also includes the concept of artificial life , since any life form that might naturally evolve elsewhere could concei...

Wobble base pair

...ure . It has comparable thermodynamic stability of the Watson-Crick base pair . Wobble base pairs are critical for the proper translation of the genetic code . The genetic code makes up for disparities in the number o...

Xanthophyll

Xanthophyll (originally phylloxanthin ) is the yellow pigment found in the leaves of most plants . It is involved in photosynthesis along with green chlorophyll , whi...

Wavelength

The wavelength is the distance between repeating units of a wave pattern. It is commonly designated by the Greek letter lambda (λ). In a sine wave, the wavelength is the distance between pe...

Vitamin

...res in trace quantities for good health, but which the organism cannot synthesize, and therefore must obt...ds or essential amino acids . Nor is it used for the large number of other nutrients that are merely health-furthering, but not strictly essential. Human...

Vision

...on can refer to: Visual perception is one of the senses . vision (religion) "Vision" can mean ... planners and change gurus play on this sense of the word. A company vision may express a corporate long-term goal - not to be confused with a m...

Optical spectrum

...tical spectrum ( light or visible spectrum ) is the portion of the electromagnetic spectrum that is visible to the human eye . There are no exact bounds to th...

Virus evolution

...onary biology that is specifically concerned with the evolution of viruses . Many viruses , in parti... RNA viruses , have fairly high mutation rates (on the order of one point mutation or more per genome per round of replication in RNA viruses) and short ge...

Virus

... biological infectious particle; for other uses of the term see virus (disambiguation) . An extensive treatment of the pluralization of the word "virus" in English is found in the article Plural of virus . A list of ...

Virus classification

...their geometry, by whether they have envelopes, by the identity of the host organism they can infect, by mode of transmission, or by the type of disease they cause. The mo...

Virology

Virology is the study of viruses and their properties. Propert...eaks See also molecular biology phage , the virus of bacteria / prokaryotes viral plaque Important publications in virology Virus cla...

Vesicular stomatitis virus

...Vesicular stomatitis virus (VSV) is a virus in the family Rhabdoviridae , order Mononegavirales . The well-known Rabies virus belongs to the same family. VSV can infect insects and mammals . It is considered harmless to humans, and is a c...

Vestibular system

The vestibular system , or balance system , is the sensory systemthat provides the dominant input about our movement and orientation inspace. Together with the cochlea, the auditory o...

Yellow fever

...s despite existence of an effective vaccine . In the past it was a source of several devastating epidemics. The disease is caused by an arbovirus of the family Flaviviridae , and is one of the smallest RNA viruses isolated from man. Mosquitos are ...

Vesicle

...ely small and enclosed compartment, separated from the cytosol by at least one lipid bilayer . Vesicle...roducts and wastes . This biomembrane enclosing the vesicle is the same as that of the outer (cellular) membrane. Thus, because of the separation, the i...

Varicella zoster virus

... known as human herpesvirus 3 (HHV-3), is one of the eight herpesviruses known to affect humans (and ...of varicella have resolved, VZV remains dormant in the nervous system of the host in the trigeminal and dorsal root ganglia . In about 10-20% of cases...

Vacuole

...aterials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor ) within the cell, exporting unwanted substances fro...

Unsolved problems in biology

...How did it start? Is life a cosmic phenomenon? Are the conditions necessary for the origin of life narrow or broad? How did life originate and diversify in hundred millions of years...

Vaccine

...y to a disease, in order to prevent or ameliorate the effects of infection by any natural or 'wild' strain of the organism. The term derives from vaccinia , the infectious viral agent of cowpox , which, when adm...

Urea cycle

...a . This cycle, also known as ornithine cycle, was the first metabolic cycle discovered (Krebs and Hensen...ance, like urea or uric acid . Insufficiency of the urea cycle occurs in some genetic disorders ( inborn errors of metabolism ), and in liver failure...

Tubulin

Tubulin is the protein which makes up microtubules . Microtubu...as three domains . γ-tubulin is important in the nucleation and polar orientation of microtubule. Tubulin binds GTP and assembles onto the (+) en...

Transport protein

...n involved in facilitated diffusion . Changes in the conformation move the binding site to the opposite side of the protein. There are 3 types of transport proteins, unipo...

Twin

...iduals (or one of two individuals) who have shared the same uterus ( womb ) and are usually, but not necessarily, born on the same day. A fetus alone in the womb is called a singleton . Due to the limited size of the mothe...

Transmembrane receptor

...lly within a cell's plasma membrane , but also in the membranes of some subcellular compartments and ...metimes to a pair of such molecules on one side of the membrane, transmembrane receptors initiate a response on the other side. In this way they play a uni...

Turgor

...o called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclos.... In a hypotonic environment, water flows across the plasma membrane into the cell (since the concentration of water is lower inside the cell than outs...

Tumor

See the article about cancer for the main article about malignant tumors. Tumor ( American English ) or tumour ( British English ) ...

Transmembrane protein

... is an integral membrane protein that spans from the internal to the external surface of the biological membrane or lipid bilayer in which it is embedded. Extractio...

Database error

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Transformation

...ings in molecular biology : Transformation is the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign DNA . Transformation is also the process by which n...

Tobacco mosaic virus

...cteristic patterns (mottling and discoloration) on the leaves (thus the name). It was the first virus to be discovered. In 1883 Adolf Mayer first described the disease t...

Database error

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Trait

... quantifiable measurement of an organism. However, the most useful traits for genetic analysis are prese...ms in different individuals. A visible trait is the final product of many molecular and biochemical processes. In most cases, information starts wit...

Tobacco mosaic virus

...cteristic patterns (mottling and discoloration) on the leaves (thus the name). It was the first virus to be discovered. In 1883 Adolf Mayer first described the disease t...

Thylakoid

...ed grana . It contains chlorophyll , which power the formation of NADPH from NADP+ and H+, and enzymes required to form ATP , NADPH, or both in photosynthesis. The stacks connect by membranous channels as a single functional compartment. The molecular mechanism of ATP generation in chloroplasts is ...

Thomas Malthus

...it was these pessimistic views that gave economics the nickname Dismal Science , the phrase was actually coined by the historian Thomas Carlyle in reference to an anti-slavery essay w...

Thomas Hunt Morgan

...45 ) was an American geneticist . He worked on the natural history , zoology , and macromutation in the fruit fly Drosophila . His most important contributions to science were in genetics ; he won the...

Thermoregulation

Thermoregulation is the ability of an organism to keep its body tempera... that keeps its temperature constant and adapts to the temperature of the environment, thermoconformer changes its body temperature according to the temp...

Mitosis

Overview of the major events in mitosis In biology , mitosis is the process of chromosome segregation and nuclear division that follows replication of the genetic mat...

Tertiary structure

In biochemistry , the tertiary structure of a protein is its overall...its physiological role inside a cell is known as the native state or sometimes the native conformation . A protein assumes tertiary structure by " fol...

T cell

... subset of lymphocytes that play a large role in the immune response . The abbreviation "T" stands for thymus , the organ in which their final stage of development occurs. There are many types of T cells: Cytoto...

Taxonomy

...#957;ομία (taxinomia) from the words taxis = order and nomos = law) may refer...either a hierarchical classification of things, or the principles underlying the classification. Almost anything, animate objects, inanimate objects, place...

Systems biology

...nd how biological systems function. By studying the relationships and interactions between various par...s hoped that eventually an understandable model of the whole system can be developed. Nevertheless, the complexity of even a "simple" organism like the ba...

Symbiogenesis

Symbiogenesis refers to the merging of two separate organisms to form a single...Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species , who proposed that chloroplasts originated from cyanobacteria captured by a pr...

Synapse

... are specialized junctions through which cells of the nervous system signal to one another and to non-...lls such as muscles or glands . Synapses form the circuits in which the neurons of the central nervous system interconnect. They are thus crucial t...

Substrate

The word substrate can mean the following: In biochemistry , a substrate is...rial printing , substrate is used to describe the base material that images will be printed onto. Depending on the printing process and end use of th...

Symbiosis

Symbiosis (pl. symbioses) (from the Greek words syn = con/plus and biono = livin...ether in more or less intimate association or even the merging of two dissimilar organisms.The term host is usually used for the larger (macro) of the tw...

Stroma

This article is about stroma in biology. For the island, see Stroma, Scotland . Stroma can re...he fluid filled area of a chloroplast outside of the thylakoid membranes wherein the light-independent reactions ( Calvin Cycle and Carbon fixation...

Stoma

...ata ) is a tiny opening or pore , found mostly on the undersurface of a plant leaf , and used for ga...ir containing carbon dioxide and oxygen enters the plant through these openings where it gets used in photosynthesis and respiration . Waste oxygen...

Stem cell

...s are primal, undifferentiated cells which have the unique potential to produce any kind of cell in the body. Many medical researchers believe stem cells have the potential to revolutionize medicine , en...

Structural biology

Structural biology is the study of the architecture and shape of biological macromolecules -- proteins and nucleic acids in particular-...

Starch

...or thickening sauces . In industry, it is used in the manufacture of adhesives , paper , and textiles...des ) called amylose and amylopectin , in which the monomers are glucose units joined to one another head-to-tail forming alpha-1,4 linkages. The ov...

Splicing (genetics)

... can be translated into protein. During splicing, the introns are removed from the mRNA using one of three methods: Protein-mediated : spliceosomes , huge molecular structures com...

Selective serotonin reuptake inhibitor

... are a class of antidepressants . They act within the brain to increase the amount of the neurotransmitter , serotonin (5-hydroxytryptamine or 5-HT), in the synaptic gap ...