Biochemistry Ch2

Question 1

What are the key features of enzymes

Answer 1

• Lower the activation energy
• Increase the rate of the reaction
• do not alter the equilibrium constant
• Are not changed or consumed in the reaction
• Are pH and temperature sensitive
• so not affect the overall change in energy
• are specific for a particular reaction or class of reactions

Question 2

Oxidoreductase

Answer 2

• Catalyze oxidation-reduction reactions
• Transfer of electrons between biological molecules
• Often involve a cofactor like electron carriers
• e donor is the reductant and e acceptor is the oxidant

Question 3

Transferases

Answer 3

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

Question 4

Kinases

Answer 4

Catalyze the transfer of a phosphate group, generally form ATP, to another molecule
- type of transferase

Question 5

Hydrolases

Answer 5

Catalyze the breaking of a compound into two molecules using the addition of water
- naming only after the substrate

Question 6

Lyases

Answer 6

• Catalyze the cleavage of a single molecule into two products
• Does not require water and doesn’t act as an oxidoreductase
• Most reversible
• opposite is a synthase

Question 7

Isomerases

Answer 7

Catalyze the rearrangement of bonds within a molecule

Question 8

Ligases

Answer 8

Catalyze addition or synthesis reactions
- generally between larger similar molecules
- often require ATP

Question 9

Cofactors and coenzymes

Answer 9

Bind to the active site of the enzyme and participate in the catalysis of the reaction
- Cofactors generally inorganic molecules or metal ions
- Coenzymes are small organic groups (majority vitamins)

Question 10

Apoenzymes

Answer 10

Enzymes without their cofactors

Question 11

Holoenzymes

Answer 11

Enzymes with their cofactors

Question 12

Prosthetic groups

Answer 12

Tightly bound cofactors or coenzymes that are necessary for enzyme function

Question 13

What are the names of the B vitamins

Answer 13

Thiamine
riboflavin
niacin
pantothenic acid
pyridoxal phosphate
biotin
folic acid
cyanocobalamin

Question 14

Lineweaver-Burk Plots

Answer 14

A double reciprocal graph of the Michaelis-Menten equation
- The x-intercept gives the value of -1/Km
- The y-intercept fives the value of 1/vmax

Question 15

Cooperativity

Answer 15

Cooperative enzymes have multiple subunits and multiple active sites
- Subunits and enzymes may exist low-affinity tense state (T) or high-affinity relaxed state (R)
- Binding of the substrate encourages the transition of other subunits from the T state to the R state, which increases the likelihood of substrate binding by these other subunits and vice versa

Question 16

Hill’s Coefficient

Answer 16

Indicates the nature of binding by the molecule
- >1, positively cooperative binding is occurring, such that after one ligand is bound the affinity of the enzyme for further ligands increase
- <1 negatively cooperative binding is occurring, such that after one ligand is bound the affinity of the enzyme for further ligands decreases
- =1, the enzyme does not exhibit cooperative behaviour

Question 17

Effect of temperature on enzymes

Answer 17

• Enzyme-catalyzed reactions double in velocity every 10 degrees increase in temp until the optimum temperature is reached
• after this activity falls off sharply, as the enzyme will denature at higher temperatures

Question 18

What is the optimal temperature of the human body

Answer 18

37 degrees C

Question 19

pH effect of enzymes

Answer 19

pH affects the ionization of the active site and can lead to denaturation of the ezyme

Question 20

What is the optimal pH of the human body

Answer 20

7.4

Question 21

Salinity effect on enzymes

Answer 21

• Not generally physiologically significant
• Can change enzyme activity in vitro
• Disrupts hydrogen and ionic bonds, causing partial change in the conformation of the enzyme and in some cases causing denaturation

Question 22

Competitive Inhibition

Answer 22

Occupancy of the active site
- substrates cannot access enzymatic binding sites
- Can be overcome by adding more substrate so that the substrate-to-inhibitor ratio is higher
- Increases the measured value of Km because the substrate concentration has to be higher to reach half the max velocity in the presence of the inhibitor

Question 23

Noncompetitive Inhibition

Answer 23

Bind to an allosteric site instead of the active site, which induces a change in enzyme conformation
- Cannot be overcome by adding more substrate
- Adding a noncompetitive inhibitor decreases the measured value of vmax because less enzyme available to react

Question 24

Mixed inhibition

Answer 24

When an inhibitor can bind to either the enzyme or the enzyme-substrate complex, but has different affinity for each
- If the inhibitor preferentially binds to the enzyme, it increases the Km value
- If the inhibitor preferentially binds to the enzyme-substrate complex, it lowers the Km value
- In either case Vmax is decreased

Question 25

Uncompetitive Inhibition

Answer 25

Binds only to the enzyme-substrate complex and essentially lock the substrate in the enzyme, preventing its release
- Conformational change that allows the uncompetitive inhibitor to bind
- Lower Km (increased affinity) and increased vmax

Question 26

Irreversible Inhibition

Answer 26

The active site is made unavailable for a prolonged period of time, or the enzyme is permanently altered

Question 27

Allosteric Enzymes

Answer 27

Alternate between active and inactive forms
- Allosteric activators or allosteric inhibitors can bind to the allosteric sites

Question 28

Covalently Modified Enzymes

Answer 28

Enzymes can be activated or deactivated by phosphorylation or dephosphorylation
- Can also undergo glycosylation, the covalent attachment of sugar moieties

Question 29

Zymogens

Answer 29

Secreted in an inactive form and must be activated
- Contain a catalytic domain and regulatory domain
- The regulatory domain must be either removed or altered to expose the active site