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Biochemistry > Enzymes L6 > Flashcards

Enzymes L6 Flashcards

1
Q

what is a bio-catalyst

A

Catalyst- speeding up a reaction without being altered

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2
Q

what are the important properties of enzymes

A

High specificity for substrates

High Catalytic rate

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3
Q

what reactions do enzymes catalyse

A

only catalyse reactions that would occur naturally

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4
Q

what is a enzyme like

A

Three dimensional molecule

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5
Q

where does the reaction occr

A

active site

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6
Q

How do Enzymes act as Catalysts

A

reduce activation energy of a reaction

interact chemically with the substrate

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7
Q

what happens in activation energy

A

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

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8
Q

what stabilises the substrate

A

Binding to enzyme stabilises substrate in Transition State

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9
Q

what are the catalytic strategies

A 
Covalent catalysis
Reactive group (often a nucleophile)
General acid-base catalysis
Proton donation  or acceptance
Metal ion catalysis
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10
Q

what are the groups of enzymes

A 
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases (synthases)
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11
Q

how are enzymes grouped

A

Grouped into classes according to type of reaction they catalyse

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12
Q

what is an EC

A

enzyme commision

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13
Q

where are ECs

A

Each enzyme has a unique Enzyme Commission (EC) number

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14
Q

what do many enzymes require

A

cofactor

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15
Q

what is an example of a cofactor

A

NAD(P)

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16
Q

what does a cofactor acts as

A

electron carrier

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17
Q

what are enzyme cofactors used by

A

several oxidoreductases

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18
Q

where are many cofactors derived from

A

vitamins

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19
Q

what factors influence enzyme activity

A 
environment
- temperature 
- pH
inhibitors 
- competitive
- non-competitive 
covalent modification
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20
Q

what is the effect of pH

A

pH changes so the charge on amino acids alters

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21
Q

why is charge important for enzymes

A

functioning

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22
Q

how does temperature increase effect enzymes

A

increases chemical reactions

Eventually protein denatures so activity is lost

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23
Q

what is a competitive inhibitor

A

inhibitor mimics substrate structure and competes for binding site

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24
Q

what is a non-competitive inhibitor

A

Inhibitor changes binding site to prevent enzyme action

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25
Q

what catalyses covalent modification

A

Catalysed by a group of enzymes Kinases

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26
Q

example of covalent modification

A

Phosphorylation

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27
Q

what can phosphorylation do

A

activate or inhibit the enzyme

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28
Q

what does enzyme kinetics describe

A

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

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29
Q

how is Vo measured in an experiment

A

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

30
Q

what is k1

A

rate at which enzyme and substrate join

31
Q

what is k2

A

rate at which enzyme-substrate complex falls apart

32
Q

what is k3

A

rate at which product formed

33
Q

how is rate of reaction determined

A

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

34
Q

why do enzymes come apart

A

Drop back to basal state – no reaction

Enzyme catalyses formation of the product, come apart at end

35
Q

what does the Michaelis-Menton Equation describe

A

Describes way which enzymes are working

36
Q

what does Michaelis-Menton Graph show

A

Exponential decline

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

37
Q

what does a Lineweaver-Burke Equation do

A

Turns curve into a straight line

38
Q

what happens if km increases

A

gradient increases

39
Q

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

A

last point as x axis is 1/[S]

40
Q

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

A

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

41
Q

what has happened if vmax changes

A

changing ability of enzyme to work maximally

42
Q

what is the Biological Significance of Vmax

A

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

43
Q

what is the Biological Significance of Km

A

Km is a measure of the enzyme affinity for its substrate

44
Q

What does it mean if Km affinity diminishes

A

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

45
Q

does substrate increase vmax

A

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

46
Q

why does the gradient change when inhibitor added

A

competitive as alter ability of substrate to join in active site

47
Q

what is the effect of enzyme inhibition on Km

A

unaffected

48
Q

what is the effect of enzyme inhibition of vmax

A

slower

49
Q

what does chymotrypsin do

A

Cleaves peptide bonds on carboxyl side of large hydrophobic amino acids

50
Q

what amino acids does chymotrypsin cleave

A

Tyrosine
Tryptophan
Phenylalanine
Methionine

51
Q

what are proteases used for

A

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

52
Q

what is the active residue in chymotrypsin

A

OH

53
Q

what is chymotrypsin

A

a protease

54
Q

what happens in Substrate Specificity

A

Hydrophobic pocket next to serine 195

Specifically binds large hydrophobic R groups

55
Q

what does the OH bond in Chymotrypsin Action

A

protects peptide bond

56
Q

how is a covalent intermediate formed in chymotrypsin action

A

Forming a covalent intermediate with the carboxyl fragment

Aminyl fragment released

57
Q

what does a histidine do in Formation of Alkoxide ion

A

Histidine acts as a base

Removes H from serine

58
Q

what is an alkoxide

A

powerful nucleophile

59
Q

what attack mechanism happens in formation of alkoxide ion

A

Nucleophilic attack on carbonyl carbon

60
Q

what bond breaks in formation of alkoxide ion

A

Peptide bond breaks

61
Q

what bond forms in formation of alkoxide ion

A

Carbonyl group forms an acyl bond with the serine

62
Q

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

A

Amino group receives H from histidine

63
Q

what attacks the acyl bond - chymotrypsin action

A

Water attacks acyl bond releasing the carbonyl fragment

64
Q

what does the water molecules attack in formation of alkoxide ion

A

Water molecule attacks the carbonyl group

65
Q

where does histidine remove H from in formation of alkoxide ion

A

Histidine removes H from the water

66
Q

where is the remaining OH group in formation alkoxide ion

A

Remaining OH group attached to carbonyl group

67
Q

what bond breaks before COOH released in formation of alkoxide ion

A

Acyl bond breaks

68
Q

what product is released from formation of alkoxide ion

A

Carboxylic acid product released

69
Q

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

A

Enzyme returns to original state

70
Q

is chymotrypsin permanently altered

A

no always converted back

Biochemistry (13 decks)

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