Enzymes

Which of the following enzymes are transferases? Select all that apply - Glycogen phosphorylase - Protein Kinase A - Amylase - Phosphoglucomutase

- Glycogen phosphorylase - Protein Kinase A

Trypsin, an enzyme found in the duodenum of the small intestine, plays an important role in breaking down proteins in ingested food. This enzyme most likely belongs to which classification(s) of enzymes? Select all that apply. - Ligase - Oxidoreductase - Hydrolase - Isomerase - Protease

- Hydrolase - Protease

What are three ways a reaction can be speed up?

- Increasing temperature - Increasing pressure - Lowering activation energy with an enzyme

Magnesium is an important cofactor for many biological reactions. One such reaction is the phosphorylation of glucose to form glucose-6-phosphate. Which statement is the most likely mechanism of action for magnesium? - Magnesium helps to stabilize the phosphate as it is transferred to glucose - Magnesium binds outside of the active site to induce a conformational change - Magnesium acts as a nucleophile in the active site to liberate bound G-6-P - Magnesium acts as a Lewis base, stabilizing the phosphate as it is transferred to glucose

- Magnesium helps to stabilize the phosphate as it is transferred to glucose

Which of the following statements about enzymes is/are true? Select all that apply - Proteins that catalyze reactions are enzymes - An enzyme reduces the activation energy of the forward reaction, while leaving the reverse reaction unchanged - Enzymes are not consumed during the catalysis of a reaction - An enzymes activity is heavily dependent on pH and temperature

- Proteins that catalyze reactions are enzymes - Enzymes are not consumed during the catalysis of a reaction - An enzymes activity is heavily dependent on pH and temperature

Of the following options, select all of the possible ways in which an enzyme can affect the rate of a biological chemical reaction - Reduce the physical distance between reactants - Increase the energy necessary for the reverse reaction to occur - Manipulate the concentration of H3O+ within the catalytic cleft - Increase the temperature within the catalytic cleft

- Reduce the physical distance between reactants - Manipulate the concentration of H3O+ within the catalytic cleft

Catalase is an enzyme found in especially high concentrations in the liver. This molecule catalyzes the conversion of the reactive oxidative species hydrogen peroxide into water and oxygen. Which of the following statements describe(s) what happens in the presence of this enzyme?

- The rate of conversion of hydrogen peroxide to water and oxygen gas is increased - The rate of conversion of water and oxygen gas to hydrogen peroxide is increased

What is noncompetitive inhibition?

- if the inhibitor binds somewhere other than the active sight blocking substrate bonding - Change the shape of the enzyme so it cannot bind to substrate

What are some factors that affect enzyme activity?

-enzyme concentration -substrate concentration -environmental conditions -inhibitors and activators

Glucose 6-phosphate dehydrogenase catalyzes a reaction involving glucose 6-phosphate. What is the most likely product formed in this reaction? - 6-Phosphogluconolactone - Glucose - Glucose 1-phosphate - Fructose 6-phosphate

6-Phosphogluconolactone

What is a cofactor? Where is it located?

A non protein part of the enzyme that some enzymes require to be active; is apart of the active site

What kind of bonds are involved in the initial binding of substrates to the active site?

Non covalent bonds

Function of Hydrolase

Catalyzes hydrolysis, cleavage of a covalent bond of water

Function of Isomerase

Catalyzes isomerization

Function of Oxidoreductases

Catalyzes oxidation-reduction reactions

Function of Lyase

Cleaves bonds non-hydrolytically

Do enzymes catalyze exergonic or endogonic reactions?

Exergonic

True or false: Enzymes are unable to affect the free energy and enthalpy changes for a given chemical reaction but are able to increase the entropy, thereby catalyzing the reaction.

False; Enzymes do not alter any thermodynamic properties for a given chemical reaction. Entropy, enthalpy and the Gibbs free energy change are all thermodynamic properties.

True or false: Based solely on the observation that in the presence of 2,3-bisphosphoglyceric acid (2,3-BPG), the metalloprotein hemoglobin exhibits a diminished ability to bind oxygen, we can conclude that 2,3-BPG is an allosteric regulator of hemoglobin.

False; In fact, 2,3-BPG is indeed an allosteric regulator of hemoglobin, but the information given in the question stem is not sufficient to reach this conclusion. In order to conclude that 2,3-BPG is an allosteric, not an orthosteric, regulator, we must have some information indicating that it does not bind at the active site of hemoglobin.

True or false: stabilization of the transition state during an enzyme catalyzed reaction led scientist to develop the lock-any-key model of enzyme-substrate interactions

False; The stabilization of the transition state is evidence arguing for the induced fit model, not the lock-and-key model

True or false: both kinases and phosphatases catalyze their respective reactions through an addition of water.

False; While a phosphatase does catalyze the removal of a phosphate through a hydrolysis reaction, a kinase does not catalyze the transfer of a phosphate through a hydrolysis reaction.

Which of the following enzymes most likely catalyzes the formation of a dipeptide from two amino acids? - Alanine racemase - Valine-tRNA ligase - Glutamate-cysteine ligase - Dipeptidyl-peptidase

Glutamate-cysteine ligase

Function of Ligase

Joins molecules together with covalent bonds

Which of the following correctly pairs allosteric and orthosteric regulators with their definitions? Respectively, orthosteric and allosteric regulators act: - Away from the active site and at the active site - Only at the active site and either at or away from the active site - Either at or away from the active site and only away from the active site - Only at the active site and only away from the active site

Only at the active site and only away from the active site; Orthosteric refers to the active site exclusively and allosteric refers to anywhere on an enzyme that is not at the active site.

There are many ways to covalently modify proteins. A kinase enzyme facilitates which covalent modification?

Phosphorylation

Which of the following characteristics regarding enzyme-substrate complexes can be explained by the induced fit, but not the lock-and-key, model? - Reduction of the activation energy of the reaction - Rigidity of the three-dimensional structure of the enzyme - Stabilization of the transition state - Enzyme specificity

Stabilization of the transition state

One key feature of the induced fit hypothesis is that the transition state of a substrate-enzyme interaction is stabilized. According to the theory, how does this occur?

The active site and the substrate gradually alter their conformations to accommodate a tight fit

In certain individuals with congestive heart failure, it was found that an overactive enzyme known as CaM Kinase II may be the culprit. Suppose a novel inhibitor of this enzyme was developed and it was shown to fit perfectly into the active site with no alteration to the enzyme's tertiary or quaternary structure. Which model of enzyme substrate interactions would be best supported by this?

This would support the lock-and-key model and not affect the induced fit model

Function of Transferase

Transfers a functional group between molecules

How does temperature affect enzyme activity?

a. as temperature increases, so does the rate of reaction because the molecules are moving faster and have a higher chance of hitting each other b. at extremely high temperatures, the enzyme is denatured due to disruption of noncovalent bonds c. lower temperatures the substrate molecules do not have enough kinetic energy for the reaction to take place even in the presence of the enzyme

What is an allosteric activator?

a. binds and puts active site in optimal configuration which favors substrate binding, higher efficiency b. noncovalent, so reversible c. also dependent on enzyme concentration

What is an allosteric inhibitor?

a. binds to enzyme and changes shape of active site so substrate cannot bind and enzyme is turned off b. binding through noncovalent interactions so are reversible c. whether or not they bind to enzyme depends on concentration d. the mechanism behind feedback inhibition

How does pH affect enzyme activity?

a. changes shape of enzyme by interacting with noncovalent bonds b. also changes shape or charge properties of the substrate so that either the substrate cannot bind to the active site or it cannot undergo catalysis c. As pH increases, enzyme activity increases until it reaches an optimal point in which enzymes denatures and as pH increases, enzyme activity decreases.

What is competitive inhibitor?

a. interfere with the active site of the enzyme so substrate cannot bind b. reversible because binding is noncovalent c. if enough substrate is added, it will outcompete the inhibitor and reach Vmax d. Vmax remains the same, Km increases

What cant enzymes change?

delta G, Keq, delta S