Polypeptide modification can convert an inactive precursor into a functional protein through cleavage, folding or chemical processing after translation in cells.
Coverage 2016–2016 · Updated 16 Jul 2026
Many translated polypeptides must be folded, cleaved or chemically modified before becoming functional proteins.
Insulin provides a required two-stage example: removal of the signal peptide converts pre-proinsulin to proinsulin; later removal of the connecting C-peptide converts proinsulin to mature insulin, whose A and B chains remain linked by disulfide bonds.
Pre-proinsulin → signal peptide removed → proinsulin folds/disulfide bonds form → C-peptide removed → functional insulin.
Cleavage changes one precursor polypeptide into the mature hormone structure able to bind its receptor appropriately.
Translation alone does not guarantee a functional protein. The insulin example is processing after translation, not alternative splicing of insulin exons.
This objective is assessed through structured response, commonly using Suggest.
Suggest
Build the answer around this relationship: A newly translated polypeptide may be an inactive precursor.
Representative question
Insulin is produced by cutting C -peptide from the precursor molecule proinsulin. Suggest why group 1 has a greater level of C-peptide than group 2.
RNA polymerase reads template DNA 3' to 5' and synthesizes RNA 5' to 3'; ribosomes translate mRNA codons in the 5' to 3' direction. Promoters mark transcription start regions and orientation; transcription factors help RNA polymerase bind and initiate in eukaryotes. Non-coding DNA does not code for polypeptide amino acid sequences and includes introns, regulatory sequences, telomeres, rRNA genes, and tRNA genes. Eukaryotic pre-mRNA is modified before export and translation by adding a 5' cap and poly-A tail and removing introns by splicing. Alternative splicing joins different exon combinations from one pre-mRNA, so one gene can produce multiple protein variants in different cells or stages. Translation initiation assembles ribosomal subunits at the start codon AUG; initiator tRNA enters the P site and A, P, and E sites organize tRNA movement. Newly made polypeptides may be folded, cleaved, or chemically modified; preproinsulin processing to active insulin is a key example. Proteasomes degrade tagged, damaged, or unneeded proteins; amino acid recycling supports new protein synthesis and proteome quality control.
