Question

Question 28 3pt 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 Question 29 3 pts MEK, a MAP kinase kinase, is activated by phosphorylation. You create a mutant MEK in which the amino acids that are normaly phosphorylated is replaced with aspartate. Predict the impact of this change on MEK activity No change Always active Always inactive

Answer 1

Answer for question number 28 : The correct option is C ( Some enzymes can be kept in an inactive formed and quickly converted to an active form when needed)

Explanation : Newly synthesised proteins do not attain their final biologically active conformation until they have been altered by one or more processing reactions called post translational modifications. In cell systems, Phosphorylation is one such modification which regulates the activity of enzymes through phosphorylation and dephosphorylation by Kinases and phosphatases respectively. These modifications occurs on the hydroxyl groups of certain Ser, Thr, and Tyr residues.

Example : Glycogen phosphorylase, which is involved in the Glycogenolysis (Break down of glycogen to glucose). Normally, it exists as inactive Phosphorylase a form which gets convereted into Phosphorylase b form by phosphorylation. So, phosphorylation converts inactive enzyme into an active enzyme.