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Science for Medicine > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

what are enzymes?

A

globular proteins that act as catalysts for biological reactions

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2
Q

how do enzymes differ from chemical catalysts? (4)

A
  • they can catalyse very high reaction rates
  • are highly specific
  • work well at mild pH/temperatures
  • can be regulated
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3
Q

what are ribozymes?

A

catalytic RNA compounds with no protein component

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4
Q

what are co-factors?

A

a non-protein component of an enzyme that is crucial to its activity (tend to me metal ions)

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5
Q

what are coenzymes?

A

complex organic molecules that are usaully produced form vitamins and help to enhance an enzymes activity

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6
Q

what are prosthetic groups?

A

cofactors covalently bonded to the enzyme or very tightly associated with the enzyme

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7
Q

what is an apoenzyme?

A

the protein component of an enzyme that contains a prosthetic group

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8
Q

what is a holoenzyme?

A

the “whole” enzyme, i.e apoenzyme plus the cofactor/s

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9
Q

what ending is usually used when naming enzymes?

A
  • ase

* name usually refers to function

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10
Q

what are the 6 classes of enzymes?

A
  • oxidoreductases
  • transferases
  • hydrolases
  • lysases
  • isomerases
  • ligases
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11
Q

what do oxidoreductases do?

A

transfer electrons

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12
Q

what do transferases do?

A

transfer groups

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13
Q

what do hydrolases do?

A

hydrolysis

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14
Q

what do lysases do?

A

form or add groups to double bonds

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15
Q

what do isomerases do?

A

transfer groups within a molecule

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16
Q

what do ligases do?

A

formation of C-C, C-S, C-O and C-N bonds

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17
Q

what do enzymes do? (3)

A
  • increase rate of spontaneous reactions
  • lower the activation energy of biochemical reactions
  • accelerate movement towards reaction equilibrium
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18
Q

how does an enzymes structure allow it function?

A

they have active sites complimentary to the transition state of the substrate/s

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19
Q

what is binding energy?

A

the energy released when enzymes form non-covalent bonds with the substrate/s

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20
Q

what do reactants need to break in order to react?

A

the energy barrier

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21
Q

how do enzymes work

A
  • reduce entropy (bring reactants closer together)
  • desolvation (substrate-enzyme bond overcome H-bonds)
  • induced fit
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22
Q

what is Vmax?

A

the maximum rate of reaction that occurs when all the active sites have been filled

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23
Q

what equation can be used to analyse reaction kinetics?

A

the michaelis-menten equation

24
Q

what does the michaelis-menten reaction deuce about reaction speeds?

A

the breakdown of ES to E + P is slower than the formation of ES form E + S

25
Q

what is another technique (graphical) used to analyse reaction kinetics?

A

Lineweaver-Burk plot

26
Q

what does the x-interecpt and y-intercept show on a lineweaver-burk plot?

A 
x-intercept = 1/Km
y-interecpt = 1/Vmax
27
Q

what is the definition of Km?

A

the ratio of rate constant of breakdown of ES to E+S cmpared to the rate constant of the formation of ES from E+S

28
Q

what does a high Km show?

A

a less stable ES complex i.e low affinity between enzyme and substrate

29
Q

what are isozymes?

A

enzymes that catalyse the same reaction

30
Q

what are the properties and location of glucokinase?

A
  • high Km (for glucose)
  • high Vmax
  • found in liver
31
Q

what properties and location does hexokinase show?

A
  • low Km
  • Low Vmax
  • found in all body cells
32
Q

what happens to glucokinase activity when blood glucose drops and why is this useful?

A

glucokinase activity drops allowing glucose released by glucokenesis to leave the liver (as it isn’t converted to glucose-6-phosphate)

33
Q

what reaction do glucokinase and hexokinase catalyse?

A

glucose + ATP —-> glucose-6-phosphate + ADP

34
Q

what do increased levels of intracellular enzymes in plasma indicate?

A

tissue damage resulting from trama, necrosis etc

35
Q

what technique can be used to separate different forms of enzymes?

A

gel electrophoresis

36
Q

how many forms of creatine phosphate are there?

A

3 forms (CK1, CK2 and CK3)

37
Q

what is a ternary complex?

A

a complex which holds all of the reacting substrates and enzyme together

38
Q

what are the diffrent types of reaction mechansims for enzyme catalysed reactions with more than one substrate?

A
  • random ordered with a ternary structure
  • ordered with a ternary structure
  • no ternary structure formed (sequential)
39
Q

what type of mechansim does lactose dehydrogenase use?

A

an ordered sequential mechanism with a ternary structure

- NADH + pyruvate —-> lactate and NAD+

40
Q

describe the mechansim of creatine kinase

A

random sequential mechansim with a ternary structure

- 2x ATP + 2x Creatine —–> 2x Phosphocreatine + 2x ADP

41
Q

describe the mechansim between amino acids and ketoacids

A

double displacement (ping-pong) mechanism in which the substrates bounce on the enzyme and then off again once they’ve reacted, meaning no ternary structure forms

42
Q

what are allosteric enzymes?

A

enzymes made up of many sub-units, all of which contain active sites

43
Q

what factors affect enzyme activity?

A
  • pH
  • temperature
  • inhibitors
44
Q

what are the different types of inhibitors and how do they work?

A

COMPETITIVE: resemble substrate and bind non-covalently to active site (lowering Km)

NON-COMPETITIVE: bind to part of enzyme that’s not the active site non-covalently (lowers Vmax)

UNCOMPETITIVE: inhibitor binds above active site after the substrate has bound, preventing the product molecules form being released

45
Q

give an example of a competitive inhibitor and explain how it functions?

A

AZT

- inhibits reverse transcriptase as it is an analogue to a DNA precursor TTP

46
Q

what are irreversible inhibitors?

A

inhibitors that bind to enzymes covalently

- e.g cyanide which binds to cytochrome c oxidase disrupting terminal respiration, starving cells of ATP

47
Q

what are the two types of regulatory enzymes?

A

allosteric enzymes and covalently modified enzymes

48
Q

give an example of feedback inhibition

A

threonine dehydrogenase which is inhibted by the final product in a pathway; l-isoleucine
- l-isoleucine binds to enzyme causing a confromational change that blocks the enzymes activity

49
Q

what is feedback inhibition?

A

a build of the end product in a pathway that slows the entire pathway by altering the enzymes activity

50
Q

what are allosteric effectors?

A

cell metabolites that bind non-covalently to part of an enzyme (non-competitive) chnaging the enzymes activity
- can be activators or inhibitors

51
Q

explain the concerted model

A

allosteric enzymes have two confromations that they randomly switch between, one conformation binds the substrate well, the other doesnt
- the binding of substrate locks the enzyme in an “open” conformation allowing other substrates to bind

52
Q

what shape of curve do allosteric enzyme kinetics show?

A

a sigmoid shape

53
Q

explain the sequential model

A

there is no flipping between confromations, instead the binding of a substrate causes a conformational change that “opens” the next sub-unit allowing a second substrate molecule to bind and so on

54
Q

what is covalent modification?

A

modification of enzyme activity through covalent bonding (often involves transfer of groups) e.g phosphorylation

55
Q

what do protein kinases do?

A

add phosphoryl groups

56
Q

what do protein phosphatases do?

A

remove phosphoryl groups

57
Q

what is proteolytic cleavage?

A

the cleavage of an inactive precursor protein (proenzyme or preprotein) to give an active protein/enzyme
e.g production of digestive enzymes (zymogens)

Science for Medicine (10 decks)

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