Chapter 2: Enzymes

Question 1

What are the 6 major enzyme classifications?

Answer 1

• oxidoreductases
• transferases
• hydrolases
• lyases
• isomerases
• ligases

Question 2

transferases

Answer 2

catalyze the movement of a functional group from one molecule to another

A + BX → AX + B

Question 3

kinases

Answer 3

transfer phosphate groups from ATP to another molecules

a type of transferase

Question 4

ligases

Answer 4

catalyze the joining of 2 molecules

A + B → AB

Question 5

what enzyme joins the 2 DNA strands?

Answer 5

DNA ligase

Question 6

oxidoreductases

Answer 6

catalyze REDOX reactions; transfer electrons between biological molecules

Question 7

2 classes of oxidoreductases

Answer 7

oxidase: oxidize molecules (remove electrons)
reductase: reduce molecules (add electrons)

Question 8

isomerases

Answer 8

catalyze the rearrangement of bonds within a molecule

A → B

convert molecules from 1 isomer to another

Question 9

hydrolases

Answer 9

catalyze the cleavage of a compound into 2 molecules by adding water

A + H2O → B + C

Question 10

lyases

Answer 10

catalyze the cleavage of a single molecule into 2 products (without using water or oxidation/reduction)

A → B + C

Question 11

lipases

Answer 11

catalyze the hydrolysis of fats

Question 12

phosphatases

Answer 12

remove phosphate

a type of transferase

Question 13

phosphorylases

Answer 13

transfer of a phosphate group from a donor (not ATP) to an acceptor molecule (often glucose)

Question 14

Typical features of cofactors and coenzymes:

Answer 14

small

ions

concnetrated in an area?

charged?

Question 15

Apoenzymes vs holoenzymes

Answer 15

apoenzymes: no cofactors or coenzymes
holoenzymes: cofactors or coenzymes

Question 16

Prosthetic groups

Answer 16

permanently attached cofactors/coenzymes? commonly metal ions

Question 17

Michaelis-Menton equation (with vMax and with Kcat)

Answer 17

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

V = Kcat [E] [S] / Km + [S]

Question 18

Catalytic efficiency

Answer 18

Kcat / Km

large Kcat = efficient; small Km = efficient

Question 19

Hill’s coefficient

Answer 19

describes cooperativity

1 = no cooperativiy

greater than 1 = positive cooperativity (binding of substrate to one unit increases affinity in others)

less than 1 = negative cooeprativity

Question 20

Effect of temperature on enzyme activity

Answer 20

velocity increases at a fairly constant rate as temperature is increased UNTIL the ideal temp is reached after which further temp increase will drop the velocity significantly as enzymes are denatured

Question 21

How does negative feedback work?

Answer 21

the products of a mechanism will inhibit an enzyme earlier in the mechanism

Question 22

What are the 4 types of reversible inhibition?

Answer 22

competitive, noncompetitive, uncompetitive, mixed

Question 23

Competitive inhibition

Answer 23

bind to active site

v max is same

km changes

Question 24

noncompetitive inhibition

Answer 24

bind to allosteric site

v max changes

km stays same (substrate still has same affinity for unaffected enzyme)

Question 25

mixed inhibition

Answer 25

km may increase or decrease

inhibitor has different affinities for enzyme and ES complex

higher affinity for ES complex = greater lower km (increases affinity of substrate for enzyme)

Question 26

uncompetitive inhibition

Answer 26

relatively permanent changes

Question 27

3 regulated enzymes:

Answer 27

zymogens, allosteric enzymes, covalently modified enzymes

Question 28

Describe allosteric enzymes

Answer 28

have allosteric sites

Question 29

Describe covalently modified enzymes

Question 30

Describe zymogens

Answer 30

inactive and must be activated

Question 31

What is Km

Answer 31

affinity of substrate for enzyme; amount of substrate bound at half Vmax?

Question 32

How do enzymes alter delta G (gibbs free energy change)?

Answer 32

it does NOT

Question 33

exergonic vs endergonic reactions; their respective delta G values

Answer 33

endergonic: consumes/requires energy (positive delta G, non spontaneous)
exergonic: releases energy (negative delta G, spontaneous)

Question 34

lock and key theory vs induced fit model

Answer 34

lock and key: enzyme has active site that perfectly matches substrate

induced fit: binding of substrate causes conformation change of enzyme to then have perfect fit with substrate (ES complex is a better fit than enzyme alone)