All Biochemistry Resources
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?
Kinase
Oxidoreductase
Ligase
Phosphatase
Isomerase
Kinase
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 #1 : Transferases And Kinases
In the last step of glycolysis, what is the name of the enzyme that converts phosphoenolpyruvate into pyruvate?
Phosphoglycerate kinase
Pyruvate kinase
Hexokinase
Phosphofructokinase-1
Aldolase
Pyruvate kinase
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 #1 : Protein Functions
Which of the following enzymes catalyzes a reaction that is the functional opposite of the reaction catalyzed by kinases?
Endonuclease
Phosphatase
Flippase
None of these
Lipase
Phosphatase
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 #2 : Transferases And Kinases
Which of the following is false regarding protein kinase A (PKA)?
cAMP binds to a regulatory domain and inhibits kinase activity
PKA utilizes ATP
PKA is comprised of 2 catalytic domains that are sequestered by 2 regulatory domains
When activated, PKA undergoes conformational changes and phosphorylates its targets
cAMP binds to a regulatory domain and inhibits kinase activity
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 #1 : 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.
Aromatic
Non-polar
Chiral
Biogenic
Polar
Polar
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 #1 : Transferases And Kinases
Which of the following is false about cyclin-dependent kinases (Cdks)?
Cdk binds to a single cyclin throughout the entire cell cycle.
In yeast cells, one Cdk protein regulates the cell cycle.
Cylcin proteins control the activity of Cdks.
Vertebrate cells have four types of Cdks.
Cdk activity rises as mitosis starts.
Cdk binds to a single cyclin throughout the entire cell cycle.
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.
All Biochemistry Resources
![Learning Tools by Varsity Tutors](https://vt-vtwa-app-assets.varsitytutors.com/assets/problems/og_image_practice_problems-9cd7cd1b01009043c4576617bc620d0d5f9d58294f59b6d6556fd8365f7440cf.jpg)