Gene Expression, Protein Transport, and DNA Mutations

Vocabulary practice flashcards covering translation, the secretory pathway, protein sorting, types of point and frameshift mutations, and DNA repair mechanisms.

Peptidyl transferase

The enzyme that forms the peptide bond between adjacent amino acids during the elongation phase of translation.

Release factor

A protein that binds to the ribosomal A site when a stop codon is reached, triggering the dissociation of the mRNA and ribosomal subunits and releasing the free polypeptide.

Formyl methionine (F-methionine)

A modified methionine bearing a formyl group that is attached to the initiator tRNA during translation initiation in prokaryotes.

Signal sequence (Signal peptide)

A specific sequence of amino acids near the N-terminus of a nascent polypeptide that serves as a molecular tag directing the protein to its cellular destination, such as the ER.

Signal recognition particle (SRP)

A cellular entity that recognizes and binds to the signal peptide of an emerging polypeptide, escorting the entire ribosome-mRNA complex to the ER membrane.

Signal peptidase

An enzyme that clips off the signal peptide from the newly completed polypeptide, releasing the protein into the ER lumen.

Glycoprotein

A protein modified with carbohydrate groups added by enzymes in the rough ER and Golgi apparatus.

Golgi apparatus

An organelle functioning as the cellular post office that modifies proteins with carbohydrates or phosphate groups and sorts them to destinations like lysosomes, the plasma membrane, or back to the ER.

Point mutation

A genetic alteration that involves the replacement or change of a single nucleotide within a DNA sequence.

Silent mutation

A point mutation in the coding segment where a changed nucleotide does not result in a change to the specified amino acid.

Missense mutation

A point mutation in which a nucleotide change causes one amino acid to be substituted for another in the resulting protein, such as the replacement of glutamic acid with valine in sickle cell disease.

Nonsense mutation

A point mutation that alters a codon to create a premature stop codon, terminating translation early.

Frameshift mutation

A mutation caused by the insertion or deletion of one or two nucleotides, which shifts the triplet reading frame of the mRNA sequence.

Proofreading function

The enzymatic ability of DNA polymerase III to recognize a mistakenly incorporated nucleotide during replication, remove it, and insert the correct base.

Thymine dimer

A DNA lesion caused by UV radiation in which two adjacent thymine bases covalently bond to one another rather than hydrogen-bonding to adenines, creating a bulge in the DNA helix.

Nucleotide excision repair

A DNA repair pathway that corrects helix-distorting damage like thymine dimers using a nuclease to excise the damaged segment, DNA polymerase II to resynthesize the gap, and DNA ligase to seal the phosphodiester backbone.