Enzymes

Question 1

6 classes of enzymes

Answer 1

Oxidoreductases - transfer electrons NADH

Transferase - group transfer reactions

Hydrolyses - hydrolysis reaction (chymotripsin) uses h2o

Lysases

Isomerise - break bonds configuration change

Ligases - join substrate molecules together condensation reactions that consume energy (atp)

Question 2

Enzyme activity

Answer 2

Rate of enzyme catalysed reaction

Question 3

What is 1.0 unit of enzyme activity?

Answer 3

Amount needed to transform:

• 1mMol of substrate into product
• per minute
• at 25 degrees

Question 4

Specific enzyme activity

Answer 4

Measure of purity.
Number of enzyme units per milligram of protein

Higher the number = more more

Question 5

Why does carbonic anhydride need to have a high enzyme activity

Answer 5

A million times per second
Homeostasis of blood pH
Homeostasis of saliva pH

Bicarbonate ions released from parotid glands to cope with H^ ions secreted by bacteria when we eat.

Question 6

What is the most important environmental factor influencing enzyme kinetics

Answer 6

Concentration of substrate

Question 7

What are factors effecting enzymatic activity

Answer 7

• Substrate conc
• Enzyme conc
• pH
• temp - rate increases with heat
• inhibitors - pharmacy

Question 8

Michael menten equation

Answer 8

K-1 [ES] + K2 [ES]

Question 9

When subrate concentration is high which rate constant is most important in forming product

Answer 9

K2

Question 10

What is the influence of [S] on enzyme activity

Answer 10

Increase [ES] which increase rate of enzyme activity

Continues until enzyme is saturated with substrate

Question 11

Initial reaction velocity

Answer 11

[P] vs time.

Multiple linear plots for different concentration of substrate

Measure product formation in direct relationship to substrate concentration

Question 12

Michaelis menten plot

Answer 12

Multiple initial velocity (varying substrate concentration) vs substrate concentration

Hyperbole
At low concentration Vo increases linear with increase [S]

At high concentration Vo increase by smaller amounts in response to increase is [S]

All moving towards Vmax (not very accurate)

Gives Km where Vo = 1/2 Vmax
A measure of enzyme activity

Question 13

Km = michaelis constant

Answer 13

A low Km that gives 1/2 Vmax = really fast

Achieve fast rate because there is high affinity to enzyme/substrate showing even a low concentration still has good result

Km= [S] when Vo = 1/2 Vmax

Measures affinity to substrate

Question 14

Vmax in menten plot?

Answer 14

The reaction rate when the active site is saturated with substrate

Question 15

Michaelis menten equation

Answer 15

Vmax ([S]
Vo = ___________

       Km + [S]

Question 16

Kcat

Answer 16

Measures efficiency

The number of substrate molecules converted to product per enzyme molecule per second

Question 17

What values of Km and Kcat would yield fastest reaction

Answer 17

High Kcat and Low Km

Question 18

Lineweaver Burke plot

Answer 18

Slope = km/ vmax

Y intercept = v max

X intercept = 1/Km

X axis = 1/ [S]
Y axis = time

Question 19

Uncompetitive inhibitors

Answer 19

Rare
Three straight lines
Allosteric
Vmax changes (down)
Km changes (up)

Question 20

Competitive inhibitors

Answer 20

Vmax DOeST change!!!

Km goes UP

Question 21

Coenzyme
Apoenzyme
Holoenzyme

Answer 21

Coenzyme weakly bound to an apoenzyme to create holoenzyme

Apoenzyme = complex enzyme minus cofactors or prosthetic group

Question 22

Metalloenzymes

Answer 22

Doesn’t bind covalently

Has non covalent interactions with ligand to help coordinate protein.

Not part of native structure but is required for activity

Metals polarise things, make more reactive which lowers activation energy. Doesn’t change Keq

Question 23

3 types of catalytic reactions

Answer 23

Covalent
Acid-base
Metal ion-catalysed