True or false: the addition of a phosphate to a protein after it is produced is an example of post-translational modification.

• A. True
• B. False
• C. Not applicable
• D. Not related

Answer: (B)

Post-translational modification is anything added to or altered on a protein after it has been synthesized. Phosphorylation fits perfectly here: kinases attach phosphate groups to specific amino acid residues (usually serine, threonine, or tyrosine) after the protein has been made. This occurs after translation and folding, often in response to cellular signals, and it can dramatically change the protein’s activity, interactions, or location. Because the modification happens after the protein is produced, it is classified as post-translational. The process is reversible by phosphatases, allowing dynamic control of protein function.