Term | Definition |
transcription | Synthesis of an RNA molecule from a DNA template. |
transcription factors | Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription. |
transcription initiation complex | The assembly of transcription factors and RNA polymerase. |
transduction | The binding of the signal molecule changes the receptor protein in some way. |
transfer RNA (tRNA) | Interpreter of a series of codons along a mRNA molecule. |
transformation | A change in genotype and phenotype due to the assimilation of external DNA by a cell. |
translation | The synthesis of a polypeptide, which occurs under the direction of mRNA. |
translocation | Change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome. |
transmembrane proteins | Integral proteins that span the membrane. |
transport | An exchange of molecules (and their kinetic energy and momentum) across the boundary between adjacent layers of a fluid or across cell membranes. |
transport protein | A membrane protein, specifically a transport protein, that has a hydrophilic channel that certain molecules or atomic ions use as a tunnel. |
transport vesicles | Vesicles in transit from one part of the cell to another. |
transposable genetic element | A segment of DNA that can move within the genome of a cell by means of a DNA or RNA intermediate; also called a transposable element. |
transposon | A transposable genetic element that moves within a genome by means of a DNA intermediate. |
triple response | A plant growth maneuver in response to mechanical stress, involving slowing of stem elongation, a thickening of the stem, and a curvature that causes the stem to start growing horizontally. |
triplet code | Three-nucleotide long set that specifies a specific amino acid for a polypeptide chain. |
trisomic | A chromosomal condition in which a particular cell has an extra copy of one chromosome, instead of the normal two. |
trophic efficiency | Percentage of production transferred from one trophic level to the next. |
trophic structure | Feeding relationships between organisms in a community. |
tropism | A growth response that results in the curvature of whole plant organs toward or away from stimuli owing to differential rates of cell elongation. |
true-breeding | Organisms that, when reproducing, create offspring of all the same variety. |
tryiacylglycerol | Glycerol and three fatty acids. |
turgid | A cell with a cell wall that has a reasonable amount of pressure but is healthy. |
turgor pressure | The pressure inside of a cell as a cell pushes itself against the cell wall. |
turnover | Seasonal changes in warm and cool water layers in lakes. |
turnover time | Standing crop biomass compared to production. |
Type I | Curve that shows low death rate at early and mid-life and drops at old age, as seen in humans and large animals. |
Type II | Curve that represents constant death rate over lifespan small animals and invertebrates. |
Type III | Curve that drops sharply at the start then levels off once individuals reach a critical age, as seen in organisms that produce large numbers of offspring. |
ultimate questions | Address evolutionary significance of a behavior. |
ultrametric trees | Diagram in which length of a branch reflects amounts of actual time. |
uniform dispersion | The pattern in which individuals are equally spaced throughout a habitat. |
vaccine | A harmless variant or derivative of a pathogen that stimulates a host's immune system to mount defenses against the pathogen. |
variation | Is demonstrated by the differences in appearance that offspring show from parents and siblings. |
vasoconstriction | Reduces blood flow and heat transfer by decreasing the diameter of superficial blood vessels. |
vasodialation | Increases in the diameter of superficial blood vessels; cools the body. |
veins | Bundles of xylem and phloem. |
vernalization | The use of cold treatment to induce a plant to flower. |
vesicle | Small membrane-bound sac that functions in moving products into, out of, and within a cell. |
vestigial structures | Are little or no importance to organism, but remain from an ancestor. |
viral envelope | A membrane that cloaks the capsid that in turn encloses a viral genome. |
virulent | A term describing a pathogen against which a plant has little specific defense. |
virulent | Viruses that reproduce only by the lytic cycle. |
voltage-gated ion channels | Channels that open or close in response to a change in the membrane potential. |
water potential | The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure. |
Watson and Crick | Developed the double helix model of DNA. |
white matter | Whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths. |
wobble | Flexibility in the base-pairing rules in which the nucleotide at the 5' end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position of a codon. |
X linked genes | Genes found on the X chromosome. |
XO system | A sex determination system in some insects in which O stands for the absence of a sex chromosome. Females are XX, Males are XO. Males produce two classes of sperm: X sperm and sperm with no chromosome. The sperm determines the sex of the offspring. |
XY system | A sex determination system in which females have two of the same kind of sex chromosome and males have two different ones. |
yeast artificial chromosome (YAC) | A cloning vector that has telomeres and a centromere that can accommodate large DNA inserts and uses the eukaryote yeast as a host cell. |
zero population growth (ZPG) | When per capita birth and death rates are equal. (r = 0) |
ZW system | A sex determination system in fish, butterflies, birds where males are ZZ and Females are ZW. The egg determines the sex of the offspring. |
zygote | Fertilized egg. Carries one set of chromosomes from each parent. |