Ch 7 Adaptive Quiz

Protein kinases use Thr, Ser, or Tyr as what?

acceptor groups for phosphoryl transfer

Proteins that acetylate histones are known as _____, whereas those that remove acetyl groups are called _____.

acetyltransferases; deacetylases

For a particular allosteric enzyme composed of several identical subunits, the binding of a substrate molecule increases the probability that the entire complex will shift to the R form. This is an example of _____.

homotropic cooperativity

What do protein kinases do?

They transfer a phosphoryl group from ATP to a protein.

A mutation in an allosteric enzyme results in a T-to-R ratio of zero. You would expect all of the following of the enzyme EXCEPT that it would _____.

exhibit sigmoidal kinetics

UTP can only inhibit ATCase in the presence of what?

CTP

Protein phosphorylation is _____.

reversible even though dephosphorylation is not the reverse reaction of phosphorylation

What is the function of cAMP in protein kinase A activity?

cAMP binds to regulatory subunits of PKA, dissociating them from the enzyme complex.

What is the function of the pseudosubstrate groups in each R chain of protein kinase A?

They prevent the entry of protein substrates into the C subunits because they are already bound to the active sites of the C subunits

What is the net equation for the sequential phosphorylation and dephosphorylation of a protein substrate?

ATP → ADP + P_i

N-(Phosphonacetyl)-L-aspartate (PALA) is a bisubstrate analog of ATCase that acts as a competitive inhibitor of the enzyme. Which of the following is TRUE?

If CTP, an allosteric inhibitor, is added to the enzyme prior to PALA, less PALA will bind than if no CTP were present.

A protein activated by protein kinase exhibits a change in its net charge in solution. This is most likely due to _____.

the two negative charges from the phosphoryl group donated by ATP

With respect to the change in activity of protein kinase A through binding of cyclic AMP, what would you NOT expect when cAMP is rapidly degraded?

movement of pseudosubstrate residues away from the enzyme catalytic site

What occurs when cAMP levels are elevated?

cAMP binds to R chains, moving pseudosubstrate sequences out of the active site and the regulatory subunit of PKA dissociates from the catalytic subunit, activating kinase activity

Your graduate student uses p-hydroxymercuribenzoate to displace zinc ions from the enzyme complex, and then assays the complex for formation of N-carbamoyl aspartate from carbamoyl phosphate and aspartate. The rate of product formation as a function of increasing substrate concentration would yield a graph that exhibits _____.

Michaelis–Menten kinetics

The key molecule that links the energy status of the cell to regulation of metabolism via protein phosphorylation is _____.

ATP

Dephosphorylation of a protein results in which product?

P_i