Question

select all that apply

which occur during posttranslational modification?

proteins join with other proteins to form quaternary structures.
a polyribosomal complex forms to increase the rate of synthesis.
exons are spliced together.
introns are removed from the sequence.
formyl-methionine is removed from the start of the polypeptide chain.
cofactors are added to proteins destined to become enzymes.

Explanation:

Analyze the definition of posttranslational modification

Posttranslational modification (PTM) refers to the covalent and enzymatic modifications of proteins following protein biosynthesis (translation). This includes folding, subunit assembly, removal of initiator amino acids, and addition of functional groups or cofactors.

Evaluate each option against the definition

• Proteins join with other proteins to form quaternary structures: Yes, assembly of multi-subunit protein complexes occurs after translation.
• A polyribosomal complex forms to increase the rate of synthesis: No, this occurs during active translation (protein synthesis).
• Exons are spliced together: No, this is a post-transcriptional modification of pre-mRNA.
• Introns are removed from the sequence: No, this is a post-transcriptional modification of pre-mRNA.
• Formyl-methionine is removed from the start of the polypeptide chain: Yes, proteolytic cleavage of the N-terminal methionine/formyl-methionine is a classic posttranslational modification.
• Cofactors are added to proteins destined to become enzymes: Yes, the incorporation of non-protein cofactors to form functional holoenzymes occurs after the polypeptide chain is synthesized.

Answer:

Question 1

• Proteins join with other proteins to form quaternary structures. (Correct answer)
• A polyribosomal complex forms to increase the rate of synthesis.
• Exons are spliced together.
• Introns are removed from the sequence.
• Formyl-methionine is removed from the start of the polypeptide chain. (Correct answer)
• Cofactors are added to proteins destined to become enzymes. (Correct answer)