Enzyme Catalysis Lec1

Question 1

What are catalysts?

Answer 1

Substance which accelerates a chemical reaction without being consumed.

Question 2

Spontaneous reactions

Answer 2

Have -ve delta G
They are too slow so they need to be accelerated
Do this using enzymes

Question 3

Ea (Activation Energy)

Answer 3

Prevents reactants becoming products instantaneously.
Energy input to convert stable reactants into unstable molecular transition state.
The Ea determines rate of reaction and the form of the transition state determines the size of the Ea.

Question 4

What does enzyme catalysis do?

Answer 4

1) Alters the transition state species
2) Destabilise the ground state
Reduced activation energy to form the transition state.

Question 5

Enzymes are?

Answer 5

Biological Catalysts.
Large Molecules held together by many non-covalent interactions.
Contain Active sites
Almost always proteins.
Act under mild reaction conditions (sensitive)

Question 6

Enzymes are specific to …

Answer 6

Type of reaction
Positional specificity
Stereospecificity (active site is asymmetrical)

Question 7

How enzymes catalyse a reaction

Answer 7

ES complex forms - substrate binds to active site

Free energy released when multiple weak bonds form between enzyme and substrate.

Question 8

Active sites

Answer 8

Small part of total volume of enzyme
On inside of enzyme
Require large protein to shield active site (don’t want water to interact)
Unique microenvironment (can exclude water)

Question 9

Substrate bound to enzymes by what attractions?

Answer 9

Electrostatic Interactions
Hydrogen Bonds
Van Der Waals Forces

Question 10

Chemical Events at an active site

Answer 10

Binding and spacial orientation of substrates (two can come together to form one)
Ionic charge interactions
Induction of strain due to structure

Question 11

What does enzymes being flexible mean/allow

Answer 11

Can change shape:
Contributes to stabilising transition state
Excludes water
Bring components of the reaction closer together

Question 12

Active site binding

Answer 12

Induced fit - substrate binds to enzyme which changes conformation to become complementary to the substrate.
Specificity of binding depends on the precise arrangement of atoms in the active site.
‘Dynamic recognition’- induced fit

Question 13

Lowering the transition state energy

Answer 13

Stabilisation lowers the energy; less energy needed for transition state/reaction to proceed.

Question 14

Enzyme Catalysis equation

Answer 14

Kcat/Kuncat

Question 15

Effects of pH on enzyme activity

Answer 15

Regulates efficiency of the catalysis
Can ionise the substrate
Can change catalytic efficiency by inducing change in structure of proteins

Question 16

Why does each enzyme have optimum pH

Answer 16

H+ ions bind to or are released from carboxyl groups and amino groups that are present on the side chains of the amino acids.
Charges on amino acids change based on pH. Important for structure.
Most enzymes optima pH is close to conditions they normally operate in.

Question 17

Temperature

Answer 17

Increased temp=increased reaction
1) increases activity (bump into each other more)
2) active site effects (reversible)
3) denaturation
Increase temperature increases flexibilty of protein allowing formation of the transition state complex.

Question 18

7 Types of enzyme groups

Answer 18

Oxidoreductases 
Transferases
Hydrolases
Lysases
Isomerases
Ligases
Translocases

Question 19

Oxidoreductases

Answer 19

Catalyse transfer of e- from doner to an acceptor.

Oxidation/Reduction

Question 20

Transferases

Answer 20

Catalyse the transfer of functional group from one molecule to another eg. Phosphate

Question 21

Hydrolases

Answer 21

Catalyse the cleavage of bonds through addition of water or vice versa. e.g. kinases

Question 22

Lysases

Answer 22

Catalyses removal of group to form a double bond or addition of group to a double bond or cleaves involving e- rearrangements.

Question 23

Isomerases

Answer 23

Catalyses intramolecular rearrangements

Question 24

Ligases

Answer 24

Catalyse reactions in which two molecules are joined

Question 25

Translocases

Answer 25

Catalyses transfer from one side of a membrane to the other