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Flashcards in ENZYMES IN DISEASES Deck (45):
1

what are enzymes?

biological catalysts

2

what do enzymes enable?

enable reactions to take place in living material that would otherwise occur only very slowly or only under very harsh conditions

3

what is the function of enzymes?

speed up the attainment of equilibrium of a reaction without altering the final equilibrium position

4

are enzymes specific?

yes

5

why are reactions that enzymes catalyse specific?

because the composition of the active site is characteristic of a single enzyme catalysing a specific reaction

6

what causes enzymes to be specific?

Only the correct substrate will bind to the active site
The specificity of binding depends on the shape of the substrate and enzyme molecule

7

do enzymes have a high or low molecular mass?

high

8

what is the amount of enzyme needed in a reaction?

very small

9

how is an enzyme recognised?

by its activity, and the initial velocity (v0) of the reaction catalysed is what we can easily measure

10

define units of enzymes

the amount of enzyme which will catalyse the transformation of
1 μmol of substrate to product in 1 min

11

what does damage to cells by acute disease lead to?

increases the permeability of the cell memb, so that cytoplasmic enzymes, like lactate dehydrogenase, leak out into the circulation and their activity can be detected in serum

12

why is the measurement of the amount of lactate dehydrogenase in the serum important?

it is of clinical importance in diagnosis and prognosis

13

After myocardial infarction does the serum lactate dehydrogenase rise or fall?

rises

14

what are the factors affecting the rate of an enzyme catalysed reaction?

Enzyme conc
Substrate conc
pH
Temperature
Inhibitors
Coenzymes, cofactors, prosthetic groups

15

what is Vmax?

the maximum velocity (rate) of the reaction. It occurs at saturating [S]

16

what is Km?

the Michaelis constant
It is equal to the substrate conc at which the rate is half of the maximum rate, Vmax.

17

what is Km a measure of?

affinity of the E for S and is the [S] needed to achieve half Vmax

18

what have high Km values?

Enzymes with low affinities for their substrate

19

what have low Km values?

Enzymes with high affinities for their substrate

20

what does an inhibitor do?

binds to the enzyme and prevents it from being active

21

what are inactivators?

Very tightly (irreversibly) bound inhibitors
they stop the enzyme-catalysed reaction Initial velocity v0 is zero.

22

what do reversibly bound inhibitors do?

reduce the initial velocity, v0, according to how much of it is bound

23

what are the 2 types of reversibly-bound inhibitors?

competitive
non-competitive

24

how do competitive inhibition work?

both the substrate, S, and the inhibitor, I, bind to the same site on the enzyme, the active site

25

what happens at very high conc of substrate?

they will displace all of the inhibitor from the active site, so there is no inhibition and the Vmax is unchanged from the non-inhibited case

26

what is the Lineweaver Burk plot?

used to determine the type inhibition caused

27

give an example of a competitive inhibitor

Methotrexate

28

what is methotrexate?

an anti-cancer drug. It is a structural analogue of tetrahydrofolate It inhibits the enzyme Tetrahydrofolate Reductase, involved in purine and pyrimidine synthesis

29

what does non-competitive inhibition involve?

Inhibitor binds at a different site to the substrate.
Inhibitor can bind to E or ES equally well.

30

in non-competitive inhibition does the binding of S change?

no, but the enzyme can no longer transform the substrate to the product as efficiently
Vmax is decreased

31

give an example of a non-competitive inhibitor

Deoxycycline

32

what is Deoxycycline?

inhibitor of the enzyme Collagenase.
It covalently binds to this enzyme.
Collagenase is a bacterial proteolytic enzyme which damages the gums.
Inactivation of this enzyme is used to treat peridontal disease.

33

what do competitive inhibitors compete with?

compete with the substrate for binding to the active site of the enzyme, reducing the affinity of enzyme for its substrate

34

how is Vmax effected in competitive inhibitors?

unaltered

35

how is Km effected in competitive inhibitors?

increased

36

where do non-competitive inhibitors bind?

at a site distant from the active site, causing a change in shape of the enzyme
reducing its effectiveness at converting substrate to product

37

how is Vmax effected in non-competitive inhibitors?

reduced

38

how is Km effected in non-competitive inhibitors?

unaltered

39

what is irreversible inhibition?

binds irreversibly and forms covalent bonds to AA residues at or near the active site

40

what does irreversible inhibition do?

alters the shape of the enzyme causing it to lose its biological activity
Permanently inactivates the enzyme

41

give examples of irreversible inhibitors

penicillin
aspirin

42

what is penicillin?

covalently binds to the enzyme Transpeptidase, which synthesises cross links in some bacterial cell walls
Inactivating this enzyme prevents the synthesis of new bacterial cell walls so kills off a bacterial infection

43

what does MRSA stand for?

Methicillin-Resistant Staphylococcus Aureus

44

what is MRSA?

β-lactam antibiotic

45

what is aspirin?

covalently binds to Cyclo-oxygenase(COX) enzymes, which add oxygen molecules to unsaturated fatty acids during the synthesises of prostaglandin