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...
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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...
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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 ...