Question

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Posttranslational regulation by phosphorylation is important because: (select all correct) Some mRNA can be kept in inactive form, and quickly be converted to active form when needed Some enzymes can be kept in an active form and be quickly converted to an inactive form when needed Some enzymes can be kept in an inactive form and be quickly converted to an active form when needed

Answer 1

Some enzymes can be kept in an active form and quickly be converted to an inactive form when needed.

Some enzymes can be kept in an inactive form and be quickly converted to an active form when needed.

Phosphorylation is one of the mechanisms for regulating the activity of enzymes. Protein phosphorylation is one of the post-translational modification mechanisms. Other post-translational modifications include glycosylation, hydroxylation, amydation, ubiquitination, nitrosylation etc. Some of these modifications has a regulatory role, particularly protein phosphorylation.

Phosphorylation of an enzyme occurs by covalent addition of a phosphate group from ATP to the hydroxyl group of amino acids like serine, threonine or tyrosine present in proteins. The phosphate groups are added by enzymes called kinases. The phosphorylation may activate some enzymes (e.g. glycogen phosphorylase, citrate lyase etc.). These are usually enzymes of catabolic reactions. Whereas some enzymes are made inactive by phosphorylation ( e.g. Glycogen synthetase, HMG CoA reductase etc). These are usually biosynthetic (anabolic) enzymes. Phospho addition is usually a reversible modification. The phosphate groups are removed from proteins by another set of enzymes called phosphatases. Phosphorylation is not used for controlling