Lecture 22- introduction to enzymes and kinetics

Question 1

Enzyme overview

Answer 1

Protein catalysts
Increase rate of chemical reactions
Bind substrates (reactants)
Release products

Question 2

Enzymes can be … during a reaction

Answer 2

Modified
But they return to their original for and aren’t used up

Question 3

Enzymes can act as a point of ….

Answer 3

Regulation

Question 4

Enzymes are key players in …. pathways

Answer 4

Metabolic

Question 5

Enzyme substrate-binding sites

Answer 5

Substrates bind to specific sites via interactions with enzyme’s amino acids
Spatial geometry dictates specifcity

Question 6

Enzyme active catalytic site

Answer 6

The region where the reaction occurs
Functional groups present include co-enzymes, metal ions and amino acid residues

Question 7

Enzyme activation energy and transition states

Answer 7

Substrate is activated by functional groups
Energy needed to form high-energy intermediate reduces

Question 8

Enzyme pH and temperature profiles

Answer 8

Enzymes have a functional pH & temp range
Increased temp -> increased reaction rate but can be denatured

Question 9

Enzymes …. the position of equilibrium in a reaction

Answer 9

Do not alter
They accelerate the establishment of the position of equilibrium

Question 10

Enzymes involved in …. reactions are more specific that those involved in …….

Answer 10

Biosynthetoc
Degredation

Question 11

Lock and key model

Answer 11

Complementary 3D surface that recognises the substrate
Substrate binds through hydrophobic, electrostatic interactions and hydrogen bonds
Binding can be prevented by steric hinderance and charge repulsion

Question 12

The induced-fit model

Answer 12

As substrates bind, enzymes undergo conformational change
Side chains of amino acids reposition
Binding interactions increase
Not a right lock but a dynamic surface

Question 13

Enzyme active site

Answer 13

Cleft or crevice formed by polypeptide chain
3D arrangement permits reacting substances to approach each other

Question 14

Enzyme transition state complex

Answer 14

Unstable high energy complex with strained electronic configuration
activation energy of formation is reduced compared ti the non-catalysed reaction
Transition state decomposes to products and enzyme returns to original form

Question 15

What are cofactors/coenzymes?

Answer 15

Molecules that help an enzyme or protein function properly

Question 16

What are tightly bound cofactors known as?

Answer 16

Prosthetic groups

Question 17

What are coenzymes usually synthesised from in humans?

Answer 17

Vitamins

Question 18

Multi-enzyme complexes

Answer 18

Formed to promote consecutive reactions in a metabolic pathway
eg. pyruvate dehydrogenase
Advantages: transit time via diffusion reduced
less interference

Question 19

Isoenzymes (isozymes)

Answer 19

Enzymes that differ in amino acid sequence but catalyse the same chemical reaction
May show different kinetic parameters
eg. lactate dehydrogenase

Question 20

Enzyme catalysed reaction equation

Answer 20

E + S ⇌ [ES] ⇌P + E

Question 21

Factors affecting initial rate of enzyme reactions

Answer 21

[substrate]
[enzyme]
ph, temp, activators, inhibitors

Question 22

Michaelis-Menten equation enzymes

Answer 22

v= (Max[S])/(Km+[S])

Question 23

Michaelis-Menten equation meaning

Answer 23

Assumes: number of molecules and is large (so large enzyme number) & % of total enzyme-bound substrate is low
Equation relates initial velocity to concentration of substrate and two parameters Km and Vmax

Question 24

Michaelis Menten: at …. concentrations ([S]»Km) all active sites are occulpied

Answer 24

high
Reaction rate is independent of [substrate]
No more enzyme substrate complexes can be formed

Question 25

What is Km in the Michaelis Menten equation?

Answer 25

Michaelis constant
Substrate concentration at which the initial rate is 1/2Vmax

Question 26

Michaelis Menten: at low concentrations ([S]«Km) active site occupancy is ….

Answer 26

Low

Question 27

What is Vmax in Michaelis Menten equation?

Answer 27

Maximum rate achieved by the system

Question 28

Low/high Km

Answer 28

Low Km= high substrate affinity
High Km= low substrate affinity

Question 29

Catalytic efficiency (η)

Answer 29

η=kcat/Km

Question 30

Maximum catalytic efficiency

Answer 30

Theoretical limit about 10⁹M⁻¹S⁻¹
Some enzymes have evolved maximum catalytic activity

Question 31

Lineweaver-Burk

Answer 31

1/V= (Km/Vmax) x (1/[S]) + (1/Vmax)
Can be used to work out Km and Vmax
Equation is same form as y=mx+c

Question 32

Enzyme units

Answer 32

1 unit of enzyme activity (U)= amount of enzyme which transforms substrate into product at an initial velocity of one micro mol per minute measured under defined assay conditions