Lecture 7 - Enzyme Catalysis and Kinetics

Question 1

What are enzymes?

Answer 1

proteins (composed of amino acids) that act as catalyst

Question 2

How are enzymes named?

Answer 2

by adding the suffix “ase” to the reacting catalyzed or the substrate transformed of a mixture

Question 3

What are the 6 major classifications of enzymes?

Answer 3

1. oxidases
2. transferases
3. hydrolyses
4. lyases
5. isomersases
6. ligases

Question 4

catalyze oxidation/reduction reactions

Answer 4

oxidases

Question 5

catalyze the transfer of functional groups from one molecule to another

Answer 5

transferases

Question 6

hydrolases

Answer 6

catalyze hydrolysis reactions

Question 7

lyases

Answer 7

catalyze the cleavage of bonds often resulting in a new double bond or ring structure’

or

catalyze the addition of groups to double bonds

Question 8

catalyze the isomer isomerization reactions; the structural rearrangement of a molecule

Answer 8

isomerases

Question 9

catalyze reactions in which two molecules are joined together

Answer 9

ligases

ex. DNA ligase

Question 10

What is the active site?

Answer 10

the region of the enzyme that bonds the substrate

it contains the residuals (amino acids) that directly participate in making or breaking of bonds

Question 11

The active site takes up a relatively _____ part of the total volume of the enzyme.

small or large?

Answer 11

small

Question 12

The active site is a 3D entity formed by groups of different parts of the _____ _____ chain.

Answer 12

amino acid

Question 13

What are two examples of non-protein comments required by some enzymes for activity.

Answer 13

1. coenzymes

2. prosthetic groups

Question 14

coenzymes

Answer 14

serve in the transfer of electrons, elements, and functional groups

can associate at different times

Question 15

Name one coenzyme.

Answer 15

ex. NADH, electron carrier

Question 16

These associate tightly to their enzymes, usually permanently.

Answer 16

prosthetic groups

Question 17

These associate loosely to their enzymes.

Answer 17

coenzymes

Question 18

Name an example of a prosthetic group.

Answer 18

Heme group in the cytochromes

cytochromes undergo redox reactions through 4 electron transfers

Question 19

State the Michaelis-Menton (M-M) equation and define each term.

Answer 19

V = Vmax [S]
_______
[S] + Km

V = rate of catalysis (# of moose of product former per _)
Vmax = maximum rate of catalysis 
[S] = substrate concentration 
Km = Michaelis-Menton coefficient or half reaction coefficient

Question 20

What does the Michaelis-Menton (M-M) kinetics/model (or saturation kinetics) predict?

Answer 20

it accounts for the kinetics of simple enzyme catalyzed reactions

Question 21

What is the assumption about V at low [S]?

Answer 21

At low [S], V increases directly proportional to [S]

the rate is first order with respect to [S]

Question 22

What is the assumption about V at high [S]?

Answer 22

enzymes become saturated with the substrate, the rate no longer increases

*the rate is zero order with respect to [S].

Question 23

At high [S], V = ___.

Answer 23

Vmax

Question 24

Km

Answer 24

Michaelis-Menton coefficent; the substrate concentration when V is half o its max value (Vmax)

when V = Vmax/2, [S] = Km

Question 25

Km represents the affinity between the _____ and the _____.

Answer 25

substrate, enzyme

Question 26

A low Km indicates

Answer 26

a strong affinity

*Vmax is reached at lower substrate concentrations

Question 27

A high indicates

Answer 27

a poor affinity

Question 28

A (high/low) Km is most ideal. Why?

Answer 28

Low because, enzymes are not overly saturated by the substrate.

Question 29

___ and ___ can be determined from rates of catalysis of different substrate concentrations; the Michaelis-Menton equations is used.

Answer 29

Km and Vmax

Question 30

competitive inhibition

Answer 30

a chemical, similar in structure to the normal substrate, competes with the substrate for the active site of the enzyme

e.g. DCE/VE

Question 31

How can competitive inhibition be overcome?

Answer 31

by increasing the concentration of the substrate

Question 32

non-competitive inhibition

Answer 32

inhibitors do not compete with the substrate for the active site

• instead the interact with another part of the enzyme

Question 33

Does increasing the substrate concentration effect non-competitive inhibitors?

Answer 33

no