Directional selection leads to fixation of the favored allele and elimination of the other allele.

TLS Online TPP Program

#Id: 3652

#Unit 3. Fundamental Processes

In many bacteria glutamate is linked to tRNAGln by the same GluRS that synthesizes Glu–tRNAGlu. The resulting Glu–tRNAGln is then converted to Gln–tRNAGln by Glu–tRNAGln amidotransferase in an ATP-requiring reaction in which glutamine is the amide donor.

TLS Online TPP Program

#Id: 3653

#Unit 3. Fundamental Processes

Some microorganisms that lack AsnRS use a similar transamidation pathway for the synthesis of Asn–tRNAAsn from Asp–tRNAAsn.

TLS Online TPP Program

#Id: 3654

#Unit 3. Fundamental Processes

The translation machinery relies on the high fidelity of the aminoacyl-tRNA synthetases to ensure the accurate decoding of each mRNA.

TLS Online TPP Program

#Id: 3655

#Unit 3. Fundamental Processes

Certain archaebacteria lack a gene for CysRS. In these cells, Cys–tRNACys is produced by a ProRS (called ProCysRS).

TLS Online TPP Program

#Id: 3656

#Unit 3. Fundamental Processes

Certain proteins, such as the enzymes glutathione peroxidase and formate dehydrogenase, contain an unusual amino acid called selenocysteine, which is part of the catalytic center of the enzymes.

TLS Online TPP Program

#Id: 3657

#Unit 3. Fundamental Processes

Human proteome contains 25 selenoproteins. Selenocysteine, sometimes called the “twenty-first amino acid,”