Biochemistry Chapter 10 Quiz

Which of the following is FALSE?

A proenzyme is phosphorylated upon activation. -Some activated zymogens are controlled by specific irreversible inhibitors. -A proenzyme is the same as a zymogen. -Proteolytic regulation is irreversible.

Molecule AE is an allosteric effector of an enzyme. In its presence, the curve of enzyme activity versus substrate concentration is shifted to the left. Which of the following is TRUE?

AE increases the affinity of the enzyme for its substrate.

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

ATP

Which of the following does NOT occur during the proteolytic activation of a protein?

ATP is hydrolyzed. -A peptide bond is hydrolyzed. -A new amino-terminal group forms. -The process is repeated several times.

Proteins that are entirely extracellular are not regulated by reversible phosphorylation because _____.

ATP, the phosphoryl-group donor for protein kinase action, is found primarily inside the cell

In phosphorylations, the phosphoryl group usually originates from _____ and is MOST often linked to _____.

ATP; Thr or Ser

Which of the following statements about allosteric enzymes is CORRECT?

Allosteric enzymes have quaternary structure.

Which of the following is the FIRST event to occur when trauma exposes tissue factor (TF)?

Factor X is activated.

Which statement about ATCase and N-(phosphonacetyl)-L-aspartate (PALA) is FALSE?

In the presence of PALA, the T state of the enzyme is stabilized. -PALA is a bisubstrate analog that acts as a competitive inhibitor of ATCase. -If CTP, an allosteric inhibitor, is added to the enzyme prior to PALA, less PALA will bind than if no CTP were present. -If sufficient PALA is present, all three ATCase active sites will be occupied by the bisubstrate analog.

What is the function of the pseudosubstrate sequence of the R subunit in PKA?

It prevents the entry of protein substrates into the catalytic site.

Dephosphorylation of a protein results in which product?

Pi

A key difference between regulation of ATCase and control of PKA activity is _____.

R and C subunits of PKA dissociate upon activation by cAMP, whereas R and C subunits in ATCase remain associated during enzyme activation

Which of the following statements about the structure of ATCase is INCORRECT?

The active sites of ATCase at located at the interface between the c and r subunits. -The substrates and allosteric effectors bind at different sites. -Reaction with mercurials dissociates each ATCase molecule into two catalytic trimers and two dimeric regulatory subunits. -ATCase consists of two kinds of subunits and a total of 12 polypeptide chains.

Which of the following statements about ATCase and its distinct regulatory and catalytic sites is FALSE?

The separated larger subunit has catalytic activity and displays sigmoidal kinetics. -The reconstituted enzyme has the same allosteric and kinetic properties as those of the native enzyme. -The larger subunit is unresponsive CTP and is the catalytic subunit. -The isolated smaller subunit can bind CTP, and is the regulatory subunit.

Which statement is FALSE regarding allosteric sites?

They are identical to the active site. -They are where allosteric effectors bind to the enzyme. -They are also called regulatory sites. -They bind compounds that are structurally different from the substrate.

Which of the following statements about protein kinases is TRUE?

They transfer a phosphoryl group from ATP to a protein.

Cooperativity yields a sigmoidal kinetic curve. Which of the following is FALSE?

This shape is typical for most enzymes. -The sigmoidal curve is a composite of two Michaelis-Menten curves. -The sigmoidal curve allows for great changes in activity as a result of small changes in substrate concentration. -The lower part of the curve shows more T state than R state.

Which statement about pancreatic trypsin inhibitor is FALSE?

Trypsin readily degrades pancreatic trypsin inhibitor.

A kinase-catalyzed reaction generates what products?

a dephosphorylated protein and Pi

Proteolytic activation involves the conversion of a precursor protein to a mature, active protein. Which of the following are CORRECT pairs of inactive precursor: active proteins?

chymotrypsinogen: chymotrypsin

The activation of chymotrypsin results in _____.

combined action of trypsin and pepsin to yield α-chymotrypsin

Allosteric enzymes are _____, where _____ at one site _____.

cooperative; activity; affects the activity at a different site

The action of which of the following enzymes is the master activation step for the activation of all the pancreatic zymogens?

enteropeptidase

The key step in the activation of trypsinogen as it enters the duodenum from the pancreas is catalyzed by _____.

enteropeptidase

The regulation of ATCase by CTP, the ultimate product of the pathway controlled by ATCase, is an example of _____.

feedback inhibition

The allosteric effect of CTP on ATCase can best be described as a _____.

heterotropic inhibition

The enzymes catalyzing phosphorylation reactions of proteins are called protein _____.

kinases

Which of the following is NOT a common covalent modification used to alter the activity of a protein?

methylation -acetylation -phosphorylation -sulfation

Which of the following is an example of an essentially irreversible covalent modification?

myristoylation of Src

When comparing chymotrypsin and chymotrypsinogen by gel electrophoresis, what would you expect to see upon staining of the gel?

one band for chymotrypsinogen and one slightly smaller band for chymotrypsin

Chronic alcohol consumption is known to increase the synthesis of several digestive enzymes in the pancreas, including trypsinogen. One might expect that under such conditions, _____ might be observed in individuals consuming large quantities of alcoholic beverages.

pancreatitis

Enzymes that remove phosphate groups from modified enzymes are known as _____.

phosphatases

Protein kinases catalyze the addition of a(n)_____ to a protein, with _____ as a donor.

phosphoryl group; ATP

Proteolytic cleavage is an important regulatory strategy in all of the following EXCEPT _____.

phosphorylation -activation of insulin -blood clotting -programmed cell death

In the R2C2complex of PKA, each R chain includes a(n) _____.

pseudosubstrate sequence

The reaction carried out by protein phosphatases _____.

regenerates the hydroxyl group on the targeted amino acid residue

Covalent modifications can do all of the following EXCEPT _____.

replicate the enzyme -decrease the activity of an enzyme -include the covalent attachment of small groups or entire proteins -increase the activity of an enzyme

During the proteolytic activation of chymotrypsinogen, several events occur to yield the mature α-chymotrypsin enzyme. All of the following events occur during this process EXCEPT _____.

residues 187 and 193 moving closer together -a substrate-specificity pocket forming that was not present in the proenzyme -Met192 moving to the surface of the enzyme -the amine group of Ile16 forming an ionic bond with Asp194

Protein phosphorylation is _____.

reversible even though dephosphorylation is not the reverse reaction of phosphorylation

In phosphorylations catalyzed by protein kinase A, a phosphate group is transferred from ATP to a(n) _____.

serine or a threonine residue within a consensus sequence

What common point is shared between both the intrinsic and extrinsic pathways of clot formation?

the activation of factor Xa

For an allosteric enzyme, you would expect all of the following EXCEPT _____.

the enzyme existing in only one state -compounds that bind to the active site being structurally different from those that bind to the regulatory site -the enzyme having regulatory sites -the active site carrying out enzymatic activity

The value L is defined as the equilibrium constant between the R and T forms. For an allosteric enzyme such as ATCase a decreased value of L means _____.

the enzyme is in the presence of its activator, ATP

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

The enzyme responsible for the activation of most of the pancreatic zymogens when they enter the duodenum is _____.

trypsin