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Glossary
A B C D E F G H I J
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tertiary structure
The three dimensional shape of a polypeptide, largely determined by the proteins
primary and secondary structures, and the environment of the polypeptide. |
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thermodynamics
Thermodynamics is the study of
energy, its conversions between various forms such as heat, and the ability of
energy to do work. |
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totipotent
Refers to cells that are neither determined or differentiated, and so are
able to develop into any cell type of the organism.
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trait
A particular phenotypic form of a character, such as 'red' heir, or
'blue' eyes. |
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transcription
Transcription
is the process of copying DNA to mRNA by an enzyme called RNA polymerase (RNAP).
Transcription is the first step of protein biosynthesis. The process of
transcription has three steps - initiation, elongation, and termination. |
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transduction
The transfer of genetic material between prokaryotic cells using a virus
as a vector. |
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transformation
Transformation has two meanings in
molecular biology:
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Transformation is the genetic alteration of a cell resulting
from the introduction, uptake and expression of foreign DNA. This is a common
technique in molecular biology. The effect was first demonstrated in 1944 by
Avery, Macleod, and McCarty, who first demonstrated gene transfer in
Streptococus pneumoniae. E.coli, which is one of the most commonly used
bacteria for transformation, normally cannot take up plasmid DNA. However,
exposure of the cells to divalent cations such as CaCl2 makes them more
permeable to DNA. This process is relatively inefficient; electric pulses can
increase the incorporation efficiency much more. An example of transformation
is bT cotton, which incorporates BT genes which afford cotton plants a degree
of protection against certain insect pests.
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Transformation is also the process by which normal cells are
converted into cells that will continue to divide without limit. Normal cells
can divide only a certain number of times before they will stop dividing.
Cells that have been transformed no longer have such a limit (for example,
cancer cells) are able to grow and divide potentially forever.
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translation
Translation
is the process of protein biosynthesis in which messenger RNA is used as a
template to produce a specific protein according to the rules specified by the
genetic code.
The key actors involved in translation are the
ribosome, the messenger RNA (mRNA), several
transfer RNAs (tRNA) as well as numerous other protein factors. Translation
proceeds in three phases: initiation, elongation, and termination.
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transposable elements
Segments of DNA that are able to move to different sites on the same
chromosome, or are able to move between different chromosomes.
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triglyceride
Triglycerides, or
triacylglycerols, are natural fats and oils, composed of glycerin
(chemically, "glycerol") and fatty acid chains.
The fatty acids are linked to the glycerin so
as to form 3 ester functional groups:
- CH2COOR-CHCOOR'-CH2-COOR"
where R, R', and R" are fatty acids;
the three fatty acids can be all different, all the same, or only two the same.
R1-COOH + R2-OH
<----> R-COO-R2 + H2O
carboxylic acid (= fatty acid) + alcohol (=
glycerol) <-----> triglyceride + water
Chain lengths of triglycerides are 16 to 22 C
atoms
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tRNA
Transfer RNA plays a critical role in the process of
translation. tRNA is the "adaptor" molecule hypothesized by Francis Crick, which
mediates recognition of the codon sequence in mRNA and allows its translation
into the appropriate amino acid.
Each amino acid (of which there are 20) has a unique tRNA.
Before translation, each tRNA is "charged" by an amino-acyl tRNA synthetase
enzyme. Each amino acid, but 'not' each codon, has a different aminoacyl tRNA
synthetase. Recognition is not mediated primarily by the anticodon, which
would require 64 separate tRNA synthetases, but rather by other sites in the
tRNA, especially critical sequences near the 3' end of the molecule.
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trp operon
The bacterial operon that contains the genes coding for enzymes involved
in tryptophan synthesis.
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