Biochemistry Enzyme Kinetics Flashcards Preview

MCAT Self Study > Biochemistry Enzyme Kinetics > Flashcards

Flashcards in Biochemistry Enzyme Kinetics Deck (32):

What are some characteristics of an enzyme?

1. Lower the activation energy
2. Increase the rate of the reaction
3. Does not alter the equilibrium constant
4. Are not changed or consumed in the reaction (which means that they will appear in both the reactants and products.)
4. Are pH- and temperature-sensitive, with optimal activity at specific pH ranges and temperatures
5. Do not affect the overall ΔG of the reaction
6. Are specific for a particular reaction or class of reactions”


What are oxidoredutases?

“catalyze oxidation–reduction reactions that involve the transfer of electrons.” Movement of hydride is key to identifying REDOX reactions.


What are transferases?

“move a functional group from one molecule to another molecule.”

Kinase is an example of a transferase moving phosphate groups.


What do hydrolases do?

“ catalyze cleavage with the addition of water.”

Most catabolic metabolism in the body is due to hydrolases.


What are lyases?

“catalyze cleavage without the addition of water and without the transfer of electrons. The reverse reaction (synthesis) is often more important biologically.”


What are isomerases?

“ catalyze the interconversion of isomers, including both constitutional isomers and stereoisomers.”


What are ligases?

“are responsible for joining two large biomolecules, often of the same type.” REQUIRE ATP, seen in genetics during dna replication.


Mnemonic for enzyme classifications?

Ligase, Isomerase, Lyase, Hydrolase, Oxidoreductase, transferase.


What is Michaelis Menten's Equation

V= Vmax (s)/ Km + (s)


Why is the statement "An increase in the substrate concentration leads to proportional increases in the rate of the reaction" false?

As the reaction initially beings, this statement is true. Once the reaction hits Vmax, this statement stops being true.


What is an apoenzyme

enzyme with no cofactor


What is a holoenzyme

enzyme with a cofactor


What is a prosthetic group

tightly binds to the enzyme in order for the enzyme to function.


What are the H2O soluble vitamis

B and C


What are the fat soluble vitamins



Sigmoidal Curve Allosterics

Rightward shift is an inhibitor
Leftward shift is an activator


Describe Competitive Inhibitors

The inhibitor binds to the active site which decreases affinity of the substrate, increases Km, and doesn't change Vmax. We can add substrate concentration in order to out compete the inhibitor. Competitive inhibition shifts the linear plot graph to the right in the x direction.


Describe Noncompetitive Inhibitors

Inhibitor binds to an allosteric site which doesn't allow for any products to occur. This change doesn't change affinity of the substrate so Km stays the same, but decreases Vmax. Shifts the linear plot graph upwards in the y direction.


Catalytic Strategy

1. Acid/ Base: hydrogen movement
2. Proximity and Orientation
3. Electrostatic Stability: stabilize charge
4. Covalent Stability: electron movement


What are cofactors

Cofactors are helper molecules that are needed for enzymes to function properly.


What are coenzymes

organic molecules that help transfer molecules in the enzymatic reaction



Reactions are said to be exergonic and spontaneous if the dG is negative. On a graph, the products have to be lower than the reactants.



Reactions are said to be endergonic and nonspontaneous if the dG is positive. On a graph, the products have to be higher than the reactants.


What is activation energy?

The activation energy is the energy input required for the reactants to proceed to form products. The EA describes how long it takes for a reaction to occur. For example, a reaction can be spontaneous, but it might takes years to complete.


What if the function of the active site on an enzyme?

The active site binds the substrate, noncovalently, in order to stabilize the transition state, orients the substrate, changes the environment, and also breaks the bonds in the substrate.


What is the lock and key model?

The substrate and enzyme are complementary to each other and will bind perfectly like a lock and key.


What is the induced fit model?

The shape of the active site is not complementary to the substrate, however, the binding of the substrate allows for proper changes in the active site.


What is Km?

Km describes the substrate concentration at .5Vmax.


Describe the michaelis menten graph at the beginning of an enzyme reaction.

When the reaction is beginning, the concentration of the substrate is linearly proportional to the rate at which the product is made. Therefore, the reaction is a first order reaction.


Describe the michaelis menten graph at the end of the enzyme reaction

At then end of the reaction, the Vmax of the reaction will be reached. Therefore, the graph will have an asymptote and be considered a zero order reaction.


Describe Irreversible Inhibitors

An inhibitor binds covalently or non-covalently to the enzyme and bind extremely tightly. Therefore, the equilibrium arrow will push all the way to the right.


Describe uncompetitive inhibition.

Formation of the ES Complex allows inhibitors to bind to allosteric site. This increases the affinity for the substrate, which decreases Km, and decreases vmax. The plot graph will shift to the left.