T

Tertiary structure describes the organization in three dimensions of all of the atoms in the polypeptide. If a protein consists of only one polypeptide chain, this level then describes the complete structure.

Thymine is one of the four bases in DNA that make up the letters ATGC, thymine is the "T". The others are adenine, guanine, and cytosine. Thymine always pairs with adenine.

Torsion angle is a very useful descriptive tool as it can describe all combinations of tetrahedral, trigonal and digonal atoms.
The torsion angle, also known as the dihedral angle, is the relative position, or angle, between the A-X bonds and the B-Y bonds when considering four atoms connected in the order A-X-Y-B.

It can also be considered as the angle between two planes defined as A-X-Y and X-Y-B. Rotations around a X-Y single bond will therefore lead to different torsion angles. The torsion angle is frequently called (tau). By convention, following the definition proposed by W. Klyne and V. Prelog (Experientia, 1960, 16, 521-523), a positive value of the torsion angle A-X-Y-B is assigned to the clockwise rotation of up to 180° necessary to bring the front atom into an eclipsed position with the rear atom.

In the first case where is positive it would be necessary to rotate A-X clockwise so that the front bond A-X eclipsed the back bond Y-B.
In the second case it is necessary to rotate the front bond B-Y clockwise to eclipse the back bond X-A; so again there is a positive torsion angle. Examine the first two cases carefully and you will see that they do represent the same molecule but viewed from opposite ends of the molecule. In the third case it is necessary to rotate the front bond A-X anti-clockwise less than 180° to eclipse the back bond Y-B; therefore the torsion angle is negative. It is also possible to define this torsion angle as positive but it would have a value of greater than 180° (remember a circle has a range of 360°).

If all substituents on one of the two bonded atoms are identical, the smallest possible torsion angle is used to define the conformation.

If on a tetrahedral atom there are two like substituents, RR and one unique substituent R', the position of the unique substituent R determines the conformational designation.

Transmembrane Domain
Refers to the domains in amphipathic membrane proteins where the hydrophobic regions traverse the lipid bilayers of the membranes, while the hydrophilic regions extend on either side of the membrane and interact with water.

tRNA naming conventions
The tRNAs in SGD have been systematically named. The names are in the format tX(anticodon)Z, where X is the one-letter code for the conjugate amino acid and Z is the one letter code for the chromosome (A is chromosome I, B is chromosome II, C is chromosome III, etc.).

Author: Tug Sezen