ch13

Translation

The process by which messenger RNA (mRNA) is translated into protein.

Ribosome

An organelle composed of large (50S) and small (30S) subunits that facilitates protein synthesis.

50S subunit

The large ribosomal subunit that contains the peptidyl (P) and exit (E) sites.

30S subunit

The small ribosomal subunit that contains the aminoacyl (A) site.

Codon

A sequence of three RNA nucleotides that specifies an amino acid or a stop signal.

Sense codon

A codon that codes for an amino acid (e.g., AUG, which is the start codon).

Nonsense codon

A codon that does not code for any amino acid (e.g., UAA, UAG, UGA).

Universal genetic code

The genetic code that is nearly the same in all organisms.

Redundant genetic code

The genetic code where some amino acids are coded by multiple codons.

Peptide bond

A covalent bond that links amino acids in a protein.

Aminoacyl-tRNA synthetase

An enzyme that attaches a specific amino acid to its corresponding tRNA.

Polycistronic mRNA

mRNA that codes for multiple proteins, typically found in prokaryotes.

Monocistronic mRNA

mRNA that codes for a single protein, typically found in eukaryotes.

Initiation of translation

The first stage of translation where the 30S ribosomal subunit binds to mRNA and the initiator tRNA binds to the start codon (AUG).

Elongation in translation

The stage of translation where amino acids are added one by one to the growing polypeptide chain.

Termination of translation

The stage where translation ends when a stop codon is reached, resulting in the release of the polypeptide.

Nonsense Suppressor Mutations

Mutations that allow the insertion of an amino acid in place of a stop codon.

Nonsense-mediated decay (NMD)

A cellular mechanism that degrades mRNA containing premature termination codons (PTCs).

Posttranslational modifications

Changes to a protein after it has been synthesized, including folding and chemical modifications.

Proteolytic Processing

The transformation of inactive protein precursors into active forms, like how proinsulin becomes insulin.

Prosthetic Groups

Non-protein components, like vitamins and metals, needed for protein function.

Protein Trafficking

The process that sends proteins to specific parts of the cell based on their signals.

Ubiquitination

The addition of ubiquitin to proteins, signaling them for destruction by the proteasome if they are faulty.

Protein Folding

The process by which a protein assumes its functional shape, often assisted by chaperone proteins.

Terminal Modifications

Chemical alterations to protein ends, such as the removal of the formyl group from fMet in bacteria.

Modification of Individual Amino Acids

Post-translational modifications like phosphorylation, acetylation, methylation, glycosylation, and carboxylation that alter protein function.

Degenerate

The genetic code is degenerate; more than one codon can code for the same amino acid.

Non-overlapping

In the genetic code, each nucleotide is part of only one codon without any shared bases.

Contiguous

Coding regions in mRNA are composed of a continuous string of codons, forming an open reading frame (ORF) without interruptions from UTRs.

Wobble

The third nucleotide in a codon can vary, allowing tRNA to recognize multiple codons due to flexibility in base pairing.

A site

The ribosomal site that accepts incoming tRNA during protein synthesis.

P site

The ribosomal site that holds the tRNA carrying the growing polypeptide chain.

E site

The ribosomal site that contains uncharged tRNA, ready to exit the ribosome.