Enzymes (LOIL 1)

Question 1

state what it is meant by the key term - catalyst

Answer 1

a catalyst is a substance or material which accelerates a chemical reaction without being consumed within the reaction

Question 2

state 3 additional introductory facts about catalysts

Answer 2

1. do not change the equilibrium constant
2. are not reagents or cofactors
3. catalysts speed up the rate of reaction around 10-1000 times

Question 3

state what it is meant by the key term - equilibrium constant

Answer 3

The equilibrium constant, K, expresses the relationship between products and reactants of a reaction at equilibrium with respect to a specific unit

Question 4

what do spontaneous reactions have ?

Answer 4

spontaneous reactions have a -ΔG

Question 5

what does the magnitude of ΔG represent ?

Answer 5

the magnitude of ΔG represents the speed of a reaction

Question 6

what is the major issue with spontaneous reactions which enzymes can aid

Answer 6

most spontaneous reactions are too slow for metabolism, living organisms need too accelerate and control chemical reactions, this can be doe by using enzymes

Question 7

what is the point of activation energy (Ea) ?

Answer 7

Ea prevents reactants becoming products instantaneously

Question 8

what is Ea

Answer 8

Ea = Gibbs free energy of activation ΔG++

Question 9

generally, what is bigger out of Ea and ΔG ?

Answer 9

generally, Ea < ΔG

Question 10

what 2 factors determine the rate of reaction

Answer 10

1. Activation Energy (Ea)

2. Transient State (TS)

Question 11

finish the sentence:

a chemical reaction that goes from substrate A to product P goes through…

Answer 11

a chemical reaction that goes from substrate A to product P goes through a Transient State (TS) that has higher free energy than P or S

Question 12

what is one way to overcome the ‘energy barrier’ ?

Answer 12

open way to overcome the ‘energy barrier’ is to put more energy into the reactants (eg - as heat)

Question 13

why may increasing heat not work within biological systems

Answer 13

heat speeds up all reactions (non-specific) including the breakdown of structures such as cell membranes and proteins

Question 14

‘Enzyme Catalysis’ does 1 of 2 things. State these 2 things, and what is the effect of it ?

Answer 14

1. alters the Transient State (TS) species, or…
2. destabilises the ‘ground state’
3. 1 or 2 = reduces Ea to form the TS

Question 15

explain what the Transient State (TS) is using 1 sentence

Answer 15

the Transient State (TS) is the least stable and most occupied species along the reaction pathway because it is the one with the highest free energy

Question 16

enzymes exhibit ‘Reaction Specificity’ in 3 ways. state these 3 ways

Answer 16

1. type of reaction (substrate, product, no bi-product)
2. positional specificity (eg - 1’ or 2’ alcohol)
3. stereospecificity (active site of proteins is asymmetrical)

Question 17

state 4 facts about the ‘E-S Complex Formation’

Answer 17

1. 1st step in enzyme catalysis
2. substrate binds to the active site
3. free energy is released when multiple weak bonds and interactions form between the enzyme and the substrate
4. weak interactions are optimised during the Transient State (TS)

Question 18

substrates are bound to enzymes by multiple weak interactions (non-covalent bonding). state the 3 types of bonds exhibited

Answer 18

1. electrostatic interactions
2. H-bonds
3. Van der Waal forces

Question 19

state 4 facts about Active Sites

Answer 19

1. unique micro-environments
2. small part of the total enzyme volume
3. internal - requires a large protein to shield the active site from outside
4. 3D cleft/crevice formed by groups that come from different parts of the amino acid sequence

Question 20

what 3 different types of chemical events occur at/within an active site ?

Answer 20

1. binding and spatial orientation of substrates
2. ionic charge interactions
3. induction of strain

Question 21

enzymes are flexible. changes to the enzyme shape can have what 4 effects ?

Answer 21

1. contribute to the stabilising of the Transient Site (TS)
2. exclude water, which could otherwise interfere with the reaction
3. bring the components of the reaction closer together
4. exert control on enzymatic activity by regulatory molecules

Question 22

how can an active site be formed ?

Answer 22

an active site can be formed by the juxtaposition of different parts of a polypeptide/protein

Question 23

state 3 effects pH can exert on enzymatic activity

Answer 23

1. regulates enzymatic activity
2. substrate ionisation effects
3. protein structural changes

Question 24

how can pH be used to study enzymes ? (2 facts)

Answer 24

1. different enzymes have different optimal pH’s
2. this is especially important in systems such as the GI tract where pH varies from 7 (oesophagus) to 2 (stomach) and to 5 in the small intestine during bile secretion

Question 25

why do enzymes have an optimal pH ? (3 facts)

Answer 25

1. H+ ions bind to, or are released from, carboxyl and amine groups that are present in the side chains of amino acids
2. charges on amino acids are important for structure (eg - ionic bridges)
3. most enzymes have pH optima close to the conditions in which they normally operate

Question 26

what can some organisms do in regards to temperature (in the contact of enzymes)

Answer 26

some organisms adapt to changes in temperature and produce slightly different forms of enzymes (isozymes)

Question 27

how does temperature effect enzymes ?

Answer 27

increased temperature increases the flexibility (movement) in the protein backbone allowing for the formation of the Transient State (TS)

Question 28

temperature can exert 3 effects on enzymes. what are they ?

Answer 28

1. increase activity
2. (reversible) active site effects
3. denaturation of the enzyme

Question 29

name the 7 categories of enzymes that you need to know

Answer 29

1. oxidoreductases
2. transferases
3. hydrolases
4. lyases
5. isomerases
6. ligases
7. translocases

Question 30

state what it is meant by the key term, and give an example of - oxidoreductases

Answer 30

1. oxidoreductases catalyse the transfer of electrons from a donor to an acceptor (H+ transfer may also occur)
2. alcohol dehydrogenase

Question 31

state what it is meant by the key term, and give an example of - transferases

Answer 31

1. transferases catalyse the transfer of a functional group (such as phosphate)
2. hexokinase

Question 32

state what it is meant by the key term, and give an example of - hydrolases

Answer 32

1. hydrolases catalyse the cleavage of bonds through the addition or removal or water
2. proteases, such as Pepsin

Question 33

state what it is meant by the key term, and give an example of - lyases

Answer 33

1. lyases catalyse the removal of a group to form a double bond, or the addition of a group to a double bond, or cleavages involving electron rearrangements
2. isocitrate (enzyme)

Question 34

state what it is meant by the key term, and give an example of - isomerases

Answer 34

1. isomerases catalyse intramolecular rearrangements

2. aconite converts between cis and trans isomers of aconitase in the TCA

Question 35

state what it is meant by the key term, and give an example of - ligases

Answer 35

1. ligases catalyse reactions in which two molecules are joined
2. DNA ligase repairs bonds between DNA strands in DNA

Question 36

state what it is meant by the key term, and give an example of - translocases

Answer 36

1. translocases catalyse transfers from one side to another (eg - across membranes)
2. glucose transporters