Which of the following types of protein modification involves the addition of a phosphate group to a serine or threonine residue?

A Phosphorylation ✓
B Glycosylation
C Ubiquitination
D Acetylation

Explanation

Phosphorylation is a type of post-translational modification that involves the addition of a phosphate group to a serine or threonine residue, which can activate or inhibit enzyme activity.

Source

Nelson and Cox (2005) Lehninger Principles of Biochemistry
Protein Metabolism Biochemistry Post-Translational Modification Easy MEDICAL Confidence: high