Enzymes Flashcards

1
Q

What is the transition state in a reaction?

A

The high energy intermediate that lies between substrate and product in a chemical reaction

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2
Q

What is the activation energy for a reaction? What does it determine?

A

The minimum energy the substrate must have to allow the reaction to occur

How likely a reaction is to occur

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3
Q

In which two ways can increase the rate of reaction?

A

Changing the;

Temperature
Concentration

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4
Q

How does increasing the temperature affect the rate of reaction?

A

Increases the rate —-> increased number of molecules with activation energy

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5
Q

How does an increased concentration of substrate increase the rate of reaction?

A

Increased chance of molecular collisions

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6
Q

What is an enzyme?

A

Biological catalysts that increase the rate of reaction by lowering the activation energy

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7
Q

Enzymes promote the formation of ……

A

The transition state

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8
Q

Do enzymes affect the reaction equilibrium?

A

No

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9
Q

Are enzymes changed after a reaction?

A

No they remain unchanged

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10
Q

What is the active site of an enzyme? What shape do they usually take?

A

Where the substrate binds and where the chemical reaction occurs

Clefts or crevices

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11
Q

Which two models exist to describe how substrates bind to an active site? Which one is more valid?

A

Lock and key model
Induced fit model

Induced fit hypothesis is considered to be more correct

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12
Q

Describe the induced fit hypothesis of substrate binding to active site.

A

The binding of a substrate induces changes in the conformation of an enzyme —> still has a similar complementary shape to the active site

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13
Q

What is V0?

A

The initial rate of reaction (at t=0)

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14
Q

A tangent to the start of an enzyme reaction curve will show what?

A

The fastest rate of reaction

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15
Q

What shape curve do enzyme rate of reaction curves usually show?

A

Rectangular hyperbola

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16
Q

What is the relationship between substrate concentration and rate of reaction?

A

Increasing the [substrate] will increase the rate of reaction up until a certain point (maximum velocity)

17
Q

What two outcomes are there for an enzyme-substrate complex?

A

Can either form product and enzyme or dissociate back to form enzyme and substrate

18
Q

What does the Michalis-menten equation predict?

A

That a plot of V0 against [S] will be a rectangular hyperbola

19
Q

What is Vmax?

A

The maximal rate of reaction when all enzyme active sites are saturated with the substrate

20
Q

What is Km?

A

The [substrate] that gives 1/2 of Vmax

21
Q

What is the relationship between the Km of an enzyme and its affinity for its substrate?

A

Low Km = high affinity

High Km = low affinity

22
Q

What is the difference in affinity and activity of hexokinase vs glucokinase?

A

Hexokinase is always active - has a low Km and high affinity

Glucokinase is only active when glucose levels peak after feeding - has a higher Km and lower affinity

23
Q

Vmax/V0 values are rates, how are they measured?

A

In amounts per unit time

24
Q

What is 1 unit?

A

The amount of enzyme that converts 1umol of substrate per minute (under standard conditions)

25
What is the relationship between the rate of an enzyme catalysed reaction and the [enzyme]?
Rate is proportional to the [enzyme]
26
What can be plotted to allow easier estimation of Vmax and Km? What shape does it take?
A lineweaver-Burk plot Straight line, linear graph
27
How is a lineweaver-Burk graph plotted?
Take reciprocals of V and [S]
28
On a lineweaver-Burk plot, the slope (the gradient) is equal to...
Km/Vmax
29
On a lineweaver-Burk plot the y intercept will be equal to...
1/Vmax
30
On a line weaver-burk plot the x intercept will be equal to...
-1/Km
31
What are three types of enzyme inhibition?
1) irreversible 2) reversible, competitive 3) reversible, non-competitive
32
What happens during irreversible enzyme inhibition? Give an example of an irreversible enzyme inhibitor.
The molecule/drug binds very tightly, usually forming covalent bonds Nerve gases e.g. Sarin
33
What is common with all reversible enzyme inhibitors?
They don't form covalent bonds and can freely dissociate
34
What happens in reversible, competitive enzyme inhibition? What is the effect on Km and Vmax?
Molecule binds to active site. Affects Km (increases) and not Vmax
35
What happens in reversible, non-competitive enzyme inhibition? What is the effect on Km and Vmax?
Binds to another site on the enzyme Affects Vmax (lowers) and not Km
36
Why does competitive inhibition have no effect on Vmax?
Increasing the substrate concentration enough will always overcome the effect of the inhibitor - Vmax can still be reached
37
How does a non-competitive enzyme inhibitor lower the Vmax?
Decreases the turnover number of the enzyme
38
What reaction does creatine kinase catalyse?
Creatine + ATP ---> Phosphocreatine + ADP
39
Serum levels of creatine kinase are indicative of what?
Myocardial infarction if levels are high as it is released by damaged myocardial cells