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13 biochemistry > L11 & L12 - enzymes & inhibitors > Flashcards

L11 & L12 - enzymes & inhibitors Flashcards

1
Q

what are ribozymes

A

RNA based enzymes

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2
Q

characteristics of enzymes?

A

increase ROR
selective
specific (due to active site)
stabilise transition state

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3
Q

name the 6 classes of enzymes

A
  1. oxidoreductases
  2. transferases
  3. hydrolases
  4. lyases
  5. isomerases
  6. ligases
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4
Q

function of oxidoreductases

A

add O2 or remove 2H

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5
Q

function of transferases

A

transfer functional groups from one molecule to another

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6
Q

function of hydrolases

A

hydrolysis reactions

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7
Q

function of lyases

A

add groups to C=C bonds

catalyse cleavage of C-C / C-O / C-N

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8
Q

function of isomerases

A 
isomerase reactions 
(transfer of functional groups within molecule)
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9
Q

function of ligases

A

form C-C / C-N bonds using ATP

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10
Q

explain lock and key theory

A

substrate fits exactly into active site

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11
Q

explain induced fit theory

A

enzyme can undergo shape changes when substrate binds due to weak interactions with the substrate

this bring functional groups into proper position to catalyse reaction

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12
Q

what type of enzyme is chymotrypsin

A

serine protease

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13
Q

what component of chymotrypsin makes it specific

A

hydrophobic pocket

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14
Q

why is chymotrypsin a ‘serine protease’

A

because it contains a serine in the catalytic triad (responsible for its catalytic activity)

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15
Q

regarding michelis menten equation, what does it mean when [s]»Km

A

[E] is rate limiting factor

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16
Q

regarding michelis Menten equation, what does it mean when [s]

A

[S] is rate limiting factor

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17
Q

what is the Lineweaver Burk plot

A

reciprocal of the michelis menten equation , which gives the format Y = M x + c

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18
Q

what shape is MM plot

A

hyperbola
x = [S]
y = velocity (V)

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19
Q

what shape is lineweaver burk plot

A

linear
X= 1/[s]
Y = 1/V

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20
Q

when may a lineweaver burk plot be used

A

when [s] cant be measured experimentally

21
Q

what is the X intercept on a lineweaver burk plot

A

Km

22
Q

disadvantage of lineweaver burk plot

A

relies on extrapolation

can be influenced by poor data distribution

23
Q

advantage of lineweaver burk plot

A

allows clearer identification of Vmax and Km

clear way of identifying different types of inhibition

24
Q

why can Km be used as indication of affinity of enzyme for substrate

A

K2 is much slower than K-1 ,
so
Km ~ K-1 / K1

25
Q

is K1 , K-1 or K2 the rate determining step

A

K2

26
Q

what does a higher Km indicate?

A

lower affinity of E for S

ES breaks down quicker than its formed

27
Q

what does a lower Km indicate

A

higher affinity of E for S

28
Q

how is enzyme action regulated?

A
  1. environmental (pH , temp )
  2. inhibitors
  3. allosteric binding sites
29
Q

effect of temp on enzyme action?

A

increases until certain point where enzymes denature

30
Q

what is a reversible inhibitor

A

binds to enzyme but can dissociate again and enzyme activity will restore to normal

31
Q

what is a reversible inhibitor

A

inhibitor binds and inactivates enzyme permanently

32
Q

what is a competitive inhibitor

A

inhibitor that competes with S for active site

33
Q

what is a non competitive inhibitor

A

an inhibitor that binds to the allosteric site of an enzyme altering its tertiary structure and distorting the active site

34
Q

what is an uncompetitive inhibitor

A

an inhibitor that only binds to ES complex

prevents production of products

35
Q

what effect does a competitive inhibitor have on Vmax and Km

A

doesn’t affect Vmax

increases Km

36
Q

how can the inhibition effects of a competitive inhibitor be overcome?

A

increasing [S]

37
Q

what effect does a non-competitive inhibitor have on Vmax and Km

A

reduces Vmax

doesn’t affect Km

38
Q

how does a competitive inhibitor affect lineweaver burk plot?

A

the line will be steeper and to the left
same Y intercept
different X intercept

39
Q

how does a non competitive inhibitor affect lineweaver burk plot?

A

will be steeper and to the left of both other lines
same X intercept as no inhibitor
different y intercept

40
Q

define allosteric inhibitors

A

bind to allosteric site which causes conformational change in all active sites - enzyme works less well

41
Q

define allosteric activators

A

bind to allosteric site and cause increase in functioning of active site

42
Q

define cooperativity

A

when the substrate works as an allosteric activator, its binding activates other active sites

43
Q

what is T state?

A

less active form of enzyme

44
Q

what is R state?

A

more active form of enzyme

45
Q

why do allosteric enzymes often catalyse regulatory steps in metabolic pathways

A
  1. small change in [s] causes large change in V allowing sensitive on/off control
  2. rapid and reversible (no covalent bonds, can dissociate)
  3. allosteric modulators can be unrelated to the E/S - one metabolic pathway can regulate another
46
Q

what shape is produced when allostery is plotted in a V / [s] graph and explain

A

sigmoidal

it is a combination of hyperbola graphs of the T and R state (pic in word doc)

47
Q

define isoenzyme

A

enzymes with different protein structures that catalyse the same reaction

48
Q

define cofactor

A

a metal ion that is required for an enzymes activity

13 biochemistry (16 decks)

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