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Principles: biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

what is Vmax?

A

the maximum velocity of an enzymes - when it cannot work any faster

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2
Q

what is the Km?

A

the substrate concentration at Vmax over 2

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3
Q

what is the V a measure of?

A

the moles of substrate converted to product per second

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4
Q

the michaelis - menten is a _____ shaped graph

A

hyperbolic

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5
Q

as the Km increases the affinity of the enzyme for the substrate ____

A

decreases

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6
Q

in the MM Model what does K1 represent ?

A

E and S forming ES

the forward rate constant for enzyme association with the substrate

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7
Q

in the MM Model what does K2 represent ?

A

ES (binding complex) forming E and P (product)

s the forward rate constant of enzyme conversion of substrate to product (P)

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8
Q

in the MM Model what does K-1 represent ?

A

ES going back to E and S

k-1 is the backwards rate constant for enzyme dissociation from the substrate.

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9
Q

What is the michaelis constant equation Km?

A

K1

basically - dissociation over association

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10
Q

BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not ______ - reaction velocity never quite reaches true ______ !

A

BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not linear - reaction velocity never quite reaches true Vmax !

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11
Q

the michaelis menton equation describes the ___of catalysis as a function of _____ concentration. This describes a hyperbola

A

describes the rate of catalysis as a function of substrate concentration. This describes a hyperbola

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12
Q

what is the michaelis menton equation?

A

Km + [S]

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13
Q

what is the straight line equation?

A

1 = Km . 1 + 1
– —— — ——–
V Vmax [S] Vmax

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14
Q

in the lineweaver burk plot Vmax =

A

Vmax = intersection of the straight line with the Y axis

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15
Q

in the lineweaver burk plot Km=

A

KM = intersection with the X axis

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16
Q

the lineweaver burk plot is a _____ _____ plot

A

double reciprocal

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17
Q

A ___ KM means that an enzyme
only needs a little substrate to
work at half-maximal velocity

A

low

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18
Q

A ___ KM means that an enzyme
needs a lot of substrate to work at
half-maximal velocity

A

high

19
Q

Enzymes can display the same ___

and have different __

A

Vmax and Km

20
Q

a clinical examples of why Vmax and Km matter would be glucose homeostasis and _____

A

MODY

maturity onset diabetes of the young

21
Q

both ___ and ___ catalyse the reaction of glucose + ATP —-> glucose-6-phosphate + ADP

A

hexokinase and glucokinase

22
Q

hexokinase has a ___ Km for glucose

A

low

23
Q

what does the ____ Km for hexokinase mean it can do?

A

Low KM maintains energy production in red
blood cells by glycolysis even if glucose
levels fall dramatically

24
Q

where is hexokinase found?

A

RBCs

25
Q

where is glucokinase found?

A

liver and pancreas

26
Q

glucokinase has a ____ Km for glucose

A

high

27
Q

what does the ___ Km for glucose mean glucokinase is able to do

A

high, High KM enables glucose sensing & homeostasis. It’s abundance in liver is regulated by insulin. Excess blood glucose is metabolised

28
Q

what happens in MODY?

A

get loss of glucokinase activity and this means loss of insulin-mediated glucose homeostasis

29
Q

look at slides for other clinical effetc - hypoxia and stuff

A

.

30
Q

what is revesible competitive inhibition

A

Inhibitor binds to the active
(catalytic) site & blocks
substrate access.

Orthosteric Inhibition - at the same site

31
Q

what is reversible non - competitive inhibition

A

Inhibitor binds to a site other than
the catalytic centre; inhibits enzyme
by changing its conformation.

Allosteric Inhibition - at different sites

32
Q

what is irrreversible non - competitive inhibition

A

Inhibition cannot be reversed. Usually involves formation or breakage of
Covalent bonds in the enzyme complex

33
Q

in competitive inhibition the ___ does not change but the ____ varies

A

vmax,

Km

34
Q

what happens to the Km in competitive inhibition?

A

it increases

35
Q

what clinical example is there of competitive inhibition in treatment

A

methanol poisening - ethanol has a much lower Km for Alcohol dehydrogenase than methanol meaning that ADH will go down the ethanol metabolism route rather than the methanol toute

36
Q

in non-competitive inhibition the ___ varies and the __ does not change

A

Vmas varies and the Km does not change

37
Q

Inhibition of rate limiting enzymes by ___ _____ s is a common mechanism of allosteric control

A

end products

38
Q

______ enzymes do NOT follow Michaelis-Menten kinetics

A

allosteric

39
Q

with allosteric enzymes increasing substrate concentration results in a ___ curve instead of a hyperbola

A

sigmoidal

40
Q

allosteric enzymes can be ___ and ___

A

activators and inhibitors

41
Q

what is an importnat example of allosteric regulation in the body

A

haemoglobin

42
Q

in haemoglobin the binding of oxygen exhibitis ____ ____

A

positive co-operativity

43
Q

what is the binding of oxygen to haemoglobin controlled by? 3 things

A
  • H+
  • CO2
  • 2,3 bisphosphoglycerate
    a side product of glycolysis
44
Q

why does myoglobin not show co-operativity ?

A

it can only bind one O2 at a time

Principles: biochemistry (7 decks)

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