Enzymes L6

Question 1

what is a bio-catalyst

Answer 1

Catalyst- speeding up a reaction without being altered

Question 2

what are the important properties of enzymes

Answer 2

High specificity for substrates

High Catalytic rate

Question 3

what reactions do enzymes catalyse

Answer 3

only catalyse reactions that would occur naturally

Question 4

what is a enzyme like

Answer 4

Three dimensional molecule

Question 5

where does the reaction occr

Answer 5

active site

Question 6

How do Enzymes act as Catalysts

Answer 6

reduce activation energy of a reaction

interact chemically with the substrate

Question 7

what happens in activation energy

Answer 7

Takes a lot of energy to reach transition state

Condition in which the substrate is ‘undecided’ can go forward and become a product or can go backward – unstable

Question 8

what stabilises the substrate

Answer 8

Binding to enzyme stabilises substrate in Transition State

Question 9

what are the catalytic strategies

Answer 9

Covalent catalysis
Reactive group (often a nucleophile)
General acid-base catalysis
Proton donation  or acceptance
Metal ion catalysis

Question 10

what are the groups of enzymes

Answer 10

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases (synthases)

Question 11

how are enzymes grouped

Answer 11

Grouped into classes according to type of reaction they catalyse

Question 12

what is an EC

Answer 12

enzyme commision

Question 13

where are ECs

Answer 13

Each enzyme has a unique Enzyme Commission (EC) number

Question 14

what do many enzymes require

Answer 14

cofactor

Question 15

what is an example of a cofactor

Answer 15

NAD(P)

Question 16

what does a cofactor acts as

Answer 16

electron carrier

Question 17

what are enzyme cofactors used by

Answer 17

several oxidoreductases

Question 18

where are many cofactors derived from

Answer 18

vitamins

Question 19

what factors influence enzyme activity

Answer 19

environment
- temperature 
- pH
inhibitors 
- competitive
- non-competitive 
covalent modification

Question 20

what is the effect of pH

Answer 20

pH changes so the charge on amino acids alters

Question 21

why is charge important for enzymes

Answer 21

functioning

Question 22

how does temperature increase effect enzymes

Answer 22

increases chemical reactions

Eventually protein denatures so activity is lost

Question 23

what is a competitive inhibitor

Answer 23

inhibitor mimics substrate structure and competes for binding site

Question 24

what is a non-competitive inhibitor

Answer 24

Inhibitor changes binding site to prevent enzyme action

Question 25

what catalyses covalent modification

Answer 25

Catalysed by a group of enzymes Kinases

Question 26

example of covalent modification

Answer 26

Phosphorylation

Question 27

what can phosphorylation do

Answer 27

activate or inhibit the enzyme

Question 28

what does enzyme kinetics describe

Answer 28

relationship between substrate concentration [S] and the rate of an enzyme reaction Vo

Question 29

how is Vo measured in an experiment

Answer 29

Add a fixed amount of enzyme to tubes containing a range of substrate concentrations Follow rate of product formation (or substrate depletion)

Question 30

what is k1

Answer 30

rate at which enzyme and substrate join

Question 31

what is k2

Answer 31

rate at which enzyme-substrate complex falls apart

Question 32

what is k3

Answer 32

rate at which product formed

Question 33

how is rate of reaction determined

Answer 33

rate at which they enzyme and substrate join and rate at which they come apart

Question 34

why do enzymes come apart

Answer 34

Drop back to basal state – no reaction | Enzyme catalyses formation of the product, come apart at end

Question 35

what does the Michaelis-Menton Equation describe

Answer 35

Describes way which enzymes are working

Question 36

what does Michaelis-Menton Graph show

Answer 36

Exponential decline | See how different things take place - e.g. if there was a mutation

Question 37

what does a Lineweaver-Burke Equation do

Answer 37

Turns curve into a straight line

Question 38

what happens if km increases

Answer 38

gradient increases

Question 39

Where is the lowest concentration of substrate in lineweaver-burke graph

Answer 39

last point as x axis is 1/[S]

Question 40

Where is the highest concentration of substrate in lineweaver-burke graph

Answer 40

nearest to y axis as x axis is 1/[S]

Question 41

what has happened if vmax changes

Answer 41

changing ability of enzyme to work maximally

Question 42

what is the Biological Significance of Vmax

Answer 42

Represents maximum catalytic rate when substrate is not limiting All enzyme is in the form of ES Enzyme saturated

Question 43

what is the Biological Significance of Km

Answer 43

Km is a measure of the enzyme affinity for its substrate

Question 44

What does it mean if Km affinity diminishes

Answer 44

does something competitive to enzyme it stop it wanting to bind to its substrate

Question 45

does substrate increase vmax

Answer 45

High substrate can overcome inhibitor thus Vmax unaffected but affinity reduced and Km increased

Question 46

why does the gradient change when inhibitor added

Answer 46

competitive as alter ability of substrate to join in active site

Question 47

what is the effect of enzyme inhibition on Km

Answer 47

unaffected

Question 48

what is the effect of enzyme inhibition of vmax

Answer 48

slower

Question 49

what does chymotrypsin do

Answer 49

Cleaves peptide bonds on carboxyl side of large hydrophobic amino acids

Question 50

what amino acids does chymotrypsin cleave

Answer 50

Tyrosine Tryptophan Phenylalanine Methionine

Question 51

what are proteases used for

Answer 51

Needed for digestion, recycling of amino acids, activation of enzymes

Question 52

what is the active residue in chymotrypsin

Answer 52

OH

Question 53

what is chymotrypsin

Answer 53

a protease

Question 54

what happens in Substrate Specificity

Answer 54

Hydrophobic pocket next to serine 195 | Specifically binds large hydrophobic R groups

Question 55

what does the OH bond in Chymotrypsin Action

Answer 55

protects peptide bond

Question 56

how is a covalent intermediate formed in chymotrypsin action

Answer 56

Forming a covalent intermediate with the carboxyl fragment | Aminyl fragment released

Question 57

what does a histidine do in Formation of Alkoxide ion

Answer 57

Histidine acts as a base | Removes H from serine

Question 58

what is an alkoxide

Answer 58

powerful nucleophile

Question 59

what attack mechanism happens in formation of alkoxide ion

Answer 59

Nucleophilic attack on carbonyl carbon

Question 60

what bond breaks in formation of alkoxide ion

Answer 60

Peptide bond breaks

Question 61

what bond forms in formation of alkoxide ion

Answer 61

Carbonyl group forms an acyl bond with the serine

Question 62

where does the amino group get H from in formation of alkoxide ion

Answer 62

Amino group receives H from histidine

Question 63

what attacks the acyl bond - chymotrypsin action

Answer 63

Water attacks acyl bond releasing the carbonyl fragment

Question 64

what does the water molecules attack in formation of alkoxide ion

Answer 64

Water molecule attacks the carbonyl group

Question 65

where does histidine remove H from in formation of alkoxide ion

Answer 65

Histidine removes H from the water

Question 66

where is the remaining OH group in formation alkoxide ion

Answer 66

Remaining OH group attached to carbonyl group

Question 67

what bond breaks before COOH released in formation of alkoxide ion

Answer 67

Acyl bond breaks

Question 68

what product is released from formation of alkoxide ion

Answer 68

Carboxylic acid product released

Question 69

what happens once Carboxylic acid product released in formation of alkoxide ion

Answer 69

Enzyme returns to original state

Question 70

is chymotrypsin permanently altered

Answer 70

no always converted back