The electronic transitions of the peptide bond occur in the far UV. The intense peak at 190 nm, and the weaker one at 210–220 nm is due to the p!p* and n!p* transitions.

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

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#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

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#Unit 3. Fundamental Processes

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

TLS Online TPP Program

#Id: 3658

#Unit 3. Fundamental Processes

Selenocysteine is incorporated into proteins with the aid of a tRNA that interprets the UGA Stop codon as a Sec codon. tRNASec is initially charged with serine in a reaction catalyzed by the same SerRS that charges tRNASer.

TLS Online TPP Program

#Id: 3659

#Unit 3. Fundamental Processes

Instead, a dedicated protein (a special elongation factor) named SELB in complex with GTP is required to deliver Sec–tRNASec to the ribosome.