Enzymes

Question 1

How many types of substrates does one enzyme bind?

Answer 1

very few - they are highly specific

Question 2

What part of an enzyme does a substrate bind to?

Answer 2

it binds to the active site

Question 3

What is the energy of activation?

Answer 3

• all chemical rxns must cross an energy barrier between substrates and products -

free energy of activation is the difference in energy between the starting substrate and the transition state

If this energy is ‘high’ then the reaction is less likely to occcur

Question 4

What effect do enzymes have on the energy of activation?

Answer 4

enzymes lower the free energy of activation

Question 5

How do enzymes lower the free energy of activation? What are the two mechanisms ?

Answer 5

They provide alternative reaction pathways with lower free energy of activation using their active site

1) geometric complimentarity - transition state stabilization
2) electronic complimentarity - AA side chains can donate/accept protons and stabilise the enzyme/substrate complex

Question 6

What do oxidoreductases do?

Answer 6

these enzmes oxidize or reduce reactions

Question 7

What do transferase enzymes do?

Answer 7

Transfer functional groups

Question 8

What do hydrolases enzymes do?

Answer 8

cleave bonds by the addition of water

Question 9

What do lyase enzymes do?

Answer 9

They cleave CC, CS and CN bonds

Question 10

What do isomerase enzymes do?

Answer 10

they interconvert isomers

Question 11

What do ligase enzymes do?

Answer 11

they catalyze bond formation

Question 12

What is the difference between cofactors and coenzymes?

Answer 12

cofactor = metal ions like Mg, Zn, or Fe

coenzyme = organic molecules like vitamins

Question 13

What is an apoenzyme?

Answer 13

enzyme without a cofactor (inactive)

Question 14

What is a haloenzyme?

Answer 14

Enzyme with a cofactor (active)

Question 15

Where do coenzymes come from?

Answer 15

They are synthesized in the body or they come from the diet

Question 16

What factors effect reaction rate?

Answer 16

temp

pH

Substrate conc.

Question 17

What is the michealis constant?

Answer 17

The michealis constant (Km) is the substrate concentration necessary to reach half of the maximum reaction velocity

Question 18

What does the Km represent?

Answer 18

the binding affinity of the enzyme for the substrate

Question 19

What is the x axis and the y axis representative of in a lineweaver burk plot?

Answer 19

x axis = 1/[s]

y axis = 1/[Vo]

Question 20

What does Hexokinase do?

Answer 20

it phosphorylates hexose sugars

Question 21

What makes an inhibitor reversible vs. irreversible?

Answer 21

reversible inhibitors bind to enzymes with non-covalent bonds - so they can be dissociated

irreversible inhibitors form covalent bonds with the enzyme therefore they cannot regain their activity - aspirin does this

Question 22

What is competitive inhibition

Answer 22

the inhibitor binds to the same site as the substrate

Question 23

What is non-competitive inhibition?

Answer 23

inhibitor and substrate bind to different sites

Question 24

What is the effect of competitive inhibition on the michaelis menton plot?

Answer 24

Vmax: stays the same

Km: increases the Km

*competitive inhibitors compete for the same substrate, the Vmax is still the same because there is no change in the enzymes inate ability to form the enzyme/substrate complex, BUT you do require more substrate to outcompete the inhibitor - therefore the Km increases*

Question 25

What is the effect of the non-compettive inhibitor on the machaelis menton graph?

Answer 25

Vmax: decreases

Km: remains constant

*a non-competitive inhibitor binds to a different active site than the substrate therefore it does effect the inherent velocity of substrate/enzyme complex. However, you cannot ‘outcompete’ the inhibitor by adding more substrate- so the Km remains the same

Question 26

Does phosphorylation activate or deactivate an enzyme?

Answer 26

dependent on the enzyme the phosphorylated form may be more or less active

*more often, however, it increases the activity of the enxyme

Question 27

What is allosteric regulation?

Answer 27

regulation of an enzyme activity by binding small molecules to sites on the subunit other than the catalytic site -

these can be positive or negative effectors

Question 28

What is a homotropic effector?

Answer 28

it is an allosteric regulator that acts as the substrate itself

the presence of substrate at one site enhances the catalytic properties of other substrate binding sites

Question 29

What is a heterotrophic effector?

Answer 29

It is an allosteric regulator that is different to the primary substrate = overall this produces a negaitive effect on the enzyme/substrate activity