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Biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

what does the letter V denote in enzyme behaviour?

A

the rate of the catalysed reaction

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2
Q

what does [S] denote in enzyme behaviour?

A

concentration of substrate

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3
Q

what is [Km] ?

A

concentration of the substrate which causes 50% Vmax

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4
Q

what is Km?

A

The Michaelis Constant

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5
Q

what is the equation for Km?

A

(k-1 + k2)/k1

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6
Q

d: k1

A

is the forward rate constant for enzyme association with the substrate

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7
Q

d: k2

A

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

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8
Q

d: k-1

A

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

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9
Q

How is Vmax and Km measured?

A

Measure initial reaction velocity, V0, at a known substrate concentration
Repeat at increasing substrate concentrations

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10
Q

what does the Michaelis-Menten equation describe?

A

the rate of catalysis as a function of substrate concentration

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11
Q

What is the equation for michaelis- menten graph?

A

V=(Vmax[S])/(Km+[S])

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12
Q

What is Vmax from linear version of MM equation?

A

y intersection

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13
Q

What is Km from linear plot of MM graph?

A

x intersection

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14
Q

what is the linear plot of MM graph called?

A

Lineweaver-Burk plot

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15
Q

what are the axis labels on MM graph?

A

y- reaction velocity (V0)

x- [S]

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16
Q

what does a low Km mean?

A

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

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17
Q

what does a high Km mean?

A

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

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18
Q

can enzymes display same Vmax and have a different Km?

A

yes

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19
Q

Why does a low Km matter in RBCs?

A

maintains energy production in RBC by glycolysis even if glucose levels fall dramatically

20
Q

Why do livers need a high Km?

A

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

21
Q

Why does regulation of HIF transcription factor require a high Km?

A

Require O2 as a substrate
High KM for O2 - even higher than atmospheric oxygen levels
Enables oxygen sensitive oxygen sensing over physiological ranges of PO2

22
Q

What is Monge’s Disease?

A

Excessively high hematocrit
Loss of arterial oxygen saturation
Affects 10% of Andean High Altitude Native population
Loss of O2 regulation of Epo production

23
Q

d: hematocrit

A

a blood test that measures the volume percentage (vol%) of red blood cells

24
Q

d:angiogenesis

A

the development of new blood vessels.

25
Q

what can excess angiogenesis lead to?

A

Hemangiomas in brain
Subcutaneous
hemangiomas
track spinal cord

26
Q

d: subcutaneous

A

under the skin

27
Q

name the two types of inhibition

A

reversible

irreversible

28
Q

give the 2 types of reversible inhibition

A

competitive

non-competative

29
Q

describe competitive reversible inhibition

A

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

30
Q

d: Orthosteric Inhibition

A

at the same site

31
Q

describe non-competitive reversible inhibition

A

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

32
Q

d:Allosteric Inhibition

A

at different sites

33
Q

describe irreversible non-competitive inhibition

A

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

34
Q

What varies in competitive inhibition, Km or Vmax?

A

Km varies

35
Q

give an example of competitive inhibition in the clinic?

A

methanol poisoning

36
Q

how can you save someone from methanol poisoning?

A

via giving them 40% ethanol in combination with dialysis and ventilation

37
Q

What varies in non-competitive inhibition, Km or Vmax?

A

Vmax varies

38
Q

describe allosteric control

A

nhibition or activation of an enzyme by a small regulatory molecule that interacts at a site (allosteric site) other than the active site (at which catalytic activity occurs)

39
Q

why is the allosteric control system extremely effective?

A

it avoids build ups of intermediates in the pathway which in some cases can be highly reactive and therefore dangerous biochemically

40
Q

how does the allosteric system avoid build ups of intermediates?

A

Many enzymes act in series in a biochemical pathway to produce an end product. In many of these cases, the end product itself acts as an inhibitor of the slowest enzyme i.e.the rate limiting enzyme in the process which usually occurs near the beginning of the pathway. This effectively shuts down the subsequent enzymes by limiting their substrate availability.

41
Q

Do allosteric enzymes follow the MM kinetics?

A

NO

42
Q

What type of curve is produced if the concentration of an allosteric enzyme is increased?

A

sigmoidal

43
Q

what does a sigmoidal curve show?

A

co-operative behaviour

allosteric factors modulate enzyme kinetic behaviour

44
Q

Give an example of allosteric regulation in the body

A

binding of oxygen to haemoglobin

45
Q

why does myoglobin not show co-operatively?

A

low Km

46
Q

what shape of curve is the MM graph?

A

hyperbolic

Biochemistry (5 decks)

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