Biochem lecture 6

enzymes

proteins that use the energy of binding to increase RATES of chemical rxns

1. Oxidoreductases

2. Transferases

3. Hydrolases

4. Lyases

5. Isomerases

6. Ligases

list the 6 different classes of enzymes

trypsin, pepsin, lysozyme, chymotrypsin

enzymes that don’t end in -ase

cofactor

additional chemical component called a ________ required by some enzymes that is inorganic

i.e. one or more inorganic ions (Fe2 , Mg2 , Mn2 , or Zn2)

coenzyme

additional chemical component called a ________ required by some enzymes that are complex organic or metalloorganic molecule

prosthetic groups

type of coenzyme that are very tightly bound to enzymes

ex: FAD, heme

apoenzyme

an inactive enzyme that lacks its necessary cofactor or coenzyme

stabilizing the TS

enzymes lower activation energy by ________________.

Active site

special environment where the rxn will occur more rapidly - separate from extracellular milieu

Transition state

point along the pathway that has the highest energy/where the decay in S and P is equally probable

activation energy

free energy change between S and transition state

Equilibrium

describes difference in free energy between S and P ground states (NOT affected by catalyst)

does not

Favorable equilibrium ____ (does/does not) imply an appreciable RATE

Reaction Intermediates

Chemical species involved in STEPS of a catalyzed reaction 

• E.g. ES, EP

slowest

Rxns with several steps are limited by the rate-limiting step → _______ (fastest/slowest) step

transition state

Enzyme’s active site is most complementary to the ________ (substrate/transition state)

do not

enzyme _____ (do/do not) affect the reaction equilibrium

do not

enzymes _____ (do/do not) change the deltaG^’o

do

Catalysts _____ (do/do not) affect the RATE of reaction

binding energy

enzymes take advantage of energy derived from enzyme-substrate interactions – _________ __________ 𝚫G_B

[S]; ½Vmax

Km = ____ when V₀ = ________

c) changes in [S] are negligible, so [S] can be treated as a constant.

The benefit of measuring the initial rate of a reaction V₀ is that at the beginning of a reaction:

a) [ES] can be measured accurately.

b) varying [S] has no effect on V₀.

c) changes in [S] are negligible, so [S] can be treated as a constant.

d) V₀ = V_max.

e) changes in K_m are negligible, so K_m can be treated as a constant.

b) It is sometimes used to hold two substrates in the optimal orientation for reaction.

Which of the following is true of the binding energy derived from enzyme-substrate interactions?

a) Most of it is derived from covalent bonds between enzyme and substrate.

b) It is sometimes used to hold two substrates in the optimal orientation for reaction.

c) It cannot provide enough energy to explain the large rate accelerations brought about by enzymes.

d) It is the result of covalent bonds formed between enzyme and substrate.

e) Most of it is used up simply binding the substrate to the enzyme.

b) bind most tightly to the transition state.

The role of an enzyme in an enzyme-catalyzed reaction is to: 

a) ensure that all of the substrate is converted to product.

b) bind most tightly to the transition state.

c) bind a transition state intermediate, such that it cannot be converted back to substrate.

d) ensure that the product is more stable than the substrate.

e) make the free-energy change for the reaction more favorable.

a) For S -> P, a catalyst shifts the reaction equilibrium to the right.

Which of the following statements is false?

a) For S -> P, a catalyst shifts the reaction equilibrium to the right.

b) In the absence of enzyme, a reaction may not occur at a detectable rate even though it has a favorable equilibrium.

c) Substrate binds to an enzyme's active site.

d) Lowering the temperature of a reaction will lower the reaction rate.

e) After a reaction, the enzyme involved becomes available to catalyze the reaction again.

d) V_max  equals the V at which [S] = 1/2 K_m.

Which of these statements about enzyme-catalyzed reactions is false?

a) At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration.

b) If enough substrate is added, the normal V_max of a reaction can be attained even in the presence of a competitive inhibitor.

c) The rate of a reaction decreases steadily with time as substrate is depleted.

d) V_max  equals the V at which [S] = 1/2 K_m.

e) The activation energy for the catalyzed reaction is less than for the uncatalyzed reaction.