Enzymes 1

Question 1

Properties of an enzyme (3)

Answer 1

• globular protein
• biological catalyst
• decrease activation energy

Question 2

what is a co-factor?

Answer 2

non-protein part of the enzyme needed for activity

without them, proteins will not be able to carry out their functions and will unfold

Question 3

In what 2 enzymes, are co-factors Fe2+ and Fe3+ found in?

Answer 3

• catalase

- peroxidase

Question 4

In what enzyme is the co factor K+ found in?

Answer 4

pyruvate kinase

Question 5

In what enzyme is the co-factor Mg2+ found in?

Answer 5

Glucose-6-phosphatase

Question 6

what is a co-enzyme?

Answer 6

complex organic molecule, usually produced from a vitamin (most vitamins in our diet produce enzymes) and help enzymes by acting as a “helper molecule”

Question 7

What is the co-enzyme for the vitamin derivative, riboflavin?

Answer 7

FAD

Question 8

what is the co-enzyme for the vitamin derivative, niacin?

Answer 8

NAD+

Question 9

what is the co-enzyme for the vitamin derivative, pantothenate?

Answer 9

Coenzyme A

Question 10

what is a prosthetic group?

Answer 10

co-factor covalently bound to the enzyme, crucial for enzyme’s function (non-protein component) which is physically linked to an amino acid in a protein

Question 11

what is an apoenzyme?

Answer 11

the inactive enzyme which needs the co-factor to activate it

Question 12

what is a holoenzyme?

Answer 12

“whole enzyme” (the apoenzyme PLUS the co-factor)

Question 13

what do oxidoreductases do?

Answer 13

transfer electrons

Question 14

what do transferases do?

Answer 14

group transfers

Question 15

what do hydrolases do?

Answer 15

hydrolysis (transfer chemical groups of water)

Question 16

what do lyases do?

Answer 16

form or add groups to double bonds

Question 17

what do isomerases do?

Answer 17

transfer groups within molecules (forms isomers)

Question 18

what do ligases do?

Answer 18

formation of C-C, C-S, C-O and C-N bonds coupled to cleavage, forms covalent linkages between molecules

Question 19

do enzymes affect the equilibrium?

Answer 19

No effect

Question 20

do enzymes make a non-spontaneous reaction spontaneous?

Answer 20

no

Question 21

do enzymes increase the rate of a spontaneous reaction?

Answer 21

yes

Question 22

what delta G value will spontaneous reactions have?

Answer 22

negative (increase in entropy and decrease in enthalpy)

Question 23

what is energy barrier?

Answer 23

energy required to position chemical groups correctly (rearrange bonds)

Question 24

In a reaction coordinate diagram, what do transition states show?

Answer 24

the moment the chemical bonds are made and broken

Question 25

does the enzyme become part of the product?

Answer 25

No, the enzyme remains separate from the reaction

Question 26

what delta G value is needed for a reaction to happen?

Answer 26

Positive Delta G (energy input needed)

Question 27

when does catalysis happen?

Answer 27

when active site is complementary to transition state

Question 28

when is the point when activation energy is significantly lowered?

Answer 28

when substrate fits into the active site AND changes its shape. (both enzyme and substrate must change shape)

Question 29

what are the 3 factors which cause the enzyme to reduce the activation energy?

Answer 29

1. entropy reduction (reducing disorder) 2. desolvation (getting rid of water by replacing substrate-aqueous bonds with substrate-enzyme bonds) 3. induced fit (conformation change occurs in enzyme)

Question 30

what are the 3 techniques which can be used to analyse an enzyme?

Answer 30

1. enzyme kinetics 2. mutagenesis 3. 3D structure

Question 31

what will happen to the initial rate of reaction if the substrate concentration is increased?

Answer 31

higher initial rate of reaction

Question 32

when can initial velocity (v0) be calculated?

Answer 32

if we have excess substrate (initial substrate conc. doesn't change)

Question 33

what is Vmax?

Answer 33

maximum reaction velocity (reaction can't proceed faster)

Question 34

what does the Michaelis-Menten equation represent? (calculates initial velocity)

Answer 34

- proposed model to account for hyperoblic curve when you plot V0 ( initial velocity) over substrate concentration - describes how reaction velocity varies with substrate concentration

Question 35

what does the first part of the M-M equation form and what type of reaction is it?

Answer 35

ES (enzyme/substrate complex) ; reversible reaction

Question 36

what does the second part of the M-M equation form and what type of reaction is it?

Answer 36

E + P ( enzyme and product made) reversible and slow

Question 37

what is the overall rate of reaction proportional to?

Answer 37

the amount of ES (enzyme/substrate complex)

Question 38

More ES would cause what to the rate of reaction?

Answer 38

it would increase rate of reaction ( and vice versa)

Question 39

what is the steady state?

Answer 39

when rate of formation of ES= rate of breakdown of ES | synthesis rate=degradation rate

Question 40

what is the rate limiting step of an enzymatic reaction?

Answer 40

breakdown of the ES complex to give free enzyme and product (since the more ES complex there is, the faster the second part of the reaction)

Question 41

what is the definition of Km (Michaelis constant)?

Answer 41

Km is the equivalent to the substrate concentration at which the initial reaction rate/velocity is half of the maximum reaction rate (1/2 Vmax)

Question 42

what is the better way of experimentally defining Vmax and Km?

Answer 42

drawing a Lineweaver- Burk plot (using the same data that was used to draw the M-M hyperbolic curve)

Question 43

what does Lineweaver-Burk plot show?

Answer 43

determines whether Vmax has been achieved, determine the Km and mechanism for enzyme inhibitors ( a straight line is obtained)

Question 44

what does a larger Km imply about ES complex?

Answer 44

less stable ES complex, less affinity between enzyme and substrate (bad affinity)

Question 45

what does a smaller Km imply about ES complex?

Answer 45

more stable ES complex, more affinity between enzyme and substrate (good affinity)

Question 46

the higher the Vmax, the higher the...

Answer 46

rate of enzyme ( faster the enzyme) and vice versa