Enzyme Kinetics Flashcards

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1
Q

Describe the protein chymotrypsin?

A

241 amino acids, 3 peptide chains A, B, C linked by disulphide bridges.

Serine protease

Secreted by the pancreas as pro-enzyme chymotrypsinogen

Does proteolysis in duodenum by hydrolysing peptide bonds

Needs aromatic side chains e.g. phenylalanine, tyrosine, tryptophan

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2
Q

What does chymotrypsin catalyse GPNA into?

A

N-Glutaryl L-Phenyl alanine and p-nitroaniline

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3
Q

What is the beer-lambert law?

A

..

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4
Q

What is the KM ( Michaelis constant ) ?

A

Concentration of substrate at which a particular enzyme works at half its maximum velocity

  • useful for comparing the strength of enzyme-substrate complexes
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5
Q

What does a Low KM indicate?

A

Tight binding of a substrate to an enzyme

  • so high KM is indicative of weak binding
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6
Q

How to calculate Vmax from equation?

A

Kcat * [Enzyme]

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7
Q

How to calculate V0 ( initial velocity ) ?

A

Vmax [S] / (Km + [S]

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8
Q

During the initial phase of the reaction, as long as the velocity remains constant, the reaction is in (x) =, with ES being formed and consumed (y)

A

x - steady state

y - at the same rate

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9
Q

Describe a Lineweaver-Burk plot:

The axis
The intercepts
The gradient

A

X axis : 1/[S]

Y axis : 1/V0

Intercept at X axis : -1/KM

Gradient : KM/Vmax

Y intercept : 1/Vmax

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10
Q

The low the Km value, (x) the affinity of the enzyme for its substrate ?

A

Higher

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11
Q

Describe a lineweaver burk plot for a competitive inhibitor vs non-competitive inhibitor vs no inhibitor?

A

Competitive inhibitor has a different X axis intercept ( -1/KM value ) to no inhibitor whilst non-competitive has the same intercept.

Competitive inhibitor has the same Y axis intercept ( Vmax ) as no inhibitor whilst non-competitive has a different intercept ( higher )

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12
Q

How can competitive inhibitors be overcome?

A

Putting in more substrate to outcompete the inhibitor = inhibits Km but nothing to Vmax

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13
Q

What is the Kcat?

A

Turnover number : number of molecules that an enzyme can process in a given unit of time.

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14
Q

How is Chymotrypsin actively inhibited?

A

By Indole - a molecule with a competitive active site. This increase Km value - lowering affinity whilst Vmax remains the same

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