Biochemistry : Transferases and Kinases

Study concepts, example questions & explanations for Biochemistry

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Transferases And Kinases

Enzymes can be regulated in a multitude of ways. One such way is by covalent modification, in which functional groups are attached to or removed from the enzyme. One such functional group that can be added to an enzyme is a phosphate group. Depending on the enzyme, addition of a phosphate group may increase or decrease that enzyme's activity. Which of the following is the general name of an enzyme that functions to add phosphate groups to its substrate?

Possible Answers:

Isomerase

Phosphatase

Ligase

Kinase

Oxidoreductase

Correct answer:

Kinase

Explanation:

The correct answer is a kinase. Kinases are enzymes that couple the hydrolysis of ATP to the addition of a phosphate group to its substrate.

Phosphatase enzymes basically function oppositely to how kinases work. Phosphatases use water to hydrolyze phosphate groups off of their substrate.

Isomerase enzymes function to interconvert the structure of molecules from one isomer to another. This means that the substrate will remain with the same molecular formula, but it will have a difference in the connectivity of its bonds.

Ligases are enzymes that work by joining two molecules together.

Oxidoreductases are enzymes that act by catalyzing oxidation and reduction reactions, which involve the transfer of electrons from one molecule to another.

Example Question #2 : Transferases And Kinases

In the last step of glycolysis, what is the name of the enzyme that converts phosphoenolpyruvate into pyruvate?

Possible Answers:

Aldolase

Pyruvate kinase

Hexokinase

Phosphofructokinase-1

Phosphoglycerate kinase

Correct answer:

Pyruvate kinase

Explanation:

The last step of glycolysis, which involves the conversion of phosphoenolpyruvate into pyruvate, is catalyzed by the enzyme pyruvate kinase, yielding one pyruvate molecule and 1 ATP. The other kinases are involved in different steps of glycolysis.

Example Question #2 : Transferases And Kinases

Which of the following enzymes catalyzes a reaction that is the functional opposite of the reaction catalyzed by kinases?

Possible Answers:

None of these

Phosphatase

Flippase

Endonuclease

Lipase

Correct answer:

Phosphatase

Explanation:

Kinases catalyze the attachment of phosphate groups to their substrates. Phosphatases specifically remove phosphate groups from their substrates, which is the opposite of the function of kinases. The other enzymes listed do not have functions that involve removal of phosphate groups. 

Example Question #1 : Transferases And Kinases

Which of the following is false regarding protein kinase A (PKA)?

Possible Answers:

PKA is comprised of 2 catalytic domains that are sequestered by 2 regulatory domains

PKA utilizes ATP

When activated, PKA undergoes conformational changes and phosphorylates its targets

cAMP binds to a regulatory domain and inhibits kinase activity

Correct answer:

cAMP binds to a regulatory domain and inhibits kinase activity

Explanation:

From it's name, we can assume that this kinase will add phosphate groups to its targets. The source of these phosphate groups is ATP. PKA has 2 catalytic, and 2 regulatory subunits. When PKA is activated, there is a conformational change that causes the regulatory subunits to fall off, and frees the catalytic (kinase) portions. When PKA is inhibited, the regulatory subunits bind to the catalytic subunits and prevent phosphorylation. PKA has many activators, but cAMP is one of the most robust and well studied activator. Therefore, cAMP binds to the regulatory subunits, but does not inhibit protein function.

Example Question #4 : Transferases And Kinases

Kinases catalyze the phosphorylation of other proteins/substrates, which may trigger their activation. Phosphorylation involves the addition of a phosphate group to the target molecule. Amino acids with a(n) __________ R-group are typically the substrates for phosphorylation. 

Possible Answers:

Chiral

Biogenic

Aromatic

Polar

Non-polar

Correct answer:

Polar

Explanation:

Polar R-groups, namely free hydroxyl groups on serine, threonine, and tyrosine, are the usual targets for phosphorylation because they are nucleophilic and can react with the phosphate group. Other R-groups are not as reactive and therefore are not ideal sites for phosphorylation. 

Example Question #4 : Protein Functions

Which of the following is false about cyclin-dependent kinases (Cdks)?

Possible Answers:

Vertebrate cells have four types of Cdks.

Cdk binds to a single cyclin throughout the entire cell cycle.

Cylcin proteins control the activity of Cdks.

In yeast cells, one Cdk protein regulates the cell cycle.

Cdk activity rises as mitosis starts.

Correct answer:

Cdk binds to a single cyclin throughout the entire cell cycle.

Explanation:

One of the features of the beginning of mitosis, and various steps in the cell cycle, is the increase of cyclin activity. This cyclin controls the action of Cdk, causing changes in the phosphorylation of proteins, influencing cell cycle events. Yeast cells use one Cdk, which changes cyclin throughout the cycle, while vetrebrate cells use four -- -Cdk,  /S-Cdk, S-Cdk, and M-Cdk. No matter the species, however, Cdk binds to various cyclins over the course of a cell's life.

Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: