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
Q

What is the relationship between the rate of an enzyme catalysed reaction and the [enzyme]?

A

Rate is proportional to the [enzyme]

26
Q

What can be plotted to allow easier estimation of Vmax and Km? What shape does it take?

A

A lineweaver-Burk plot

Straight line, linear graph

27
Q

How is a lineweaver-Burk graph plotted?

A

Take reciprocals of V and [S]

28
Q

On a lineweaver-Burk plot, the slope (the gradient) is equal to…

A

Km/Vmax

29
Q

On a lineweaver-Burk plot the y intercept will be equal to…

A

1/Vmax

30
Q

On a line weaver-burk plot the x intercept will be equal to…

A

-1/Km

31
Q

What are three types of enzyme inhibition?

A

1) irreversible
2) reversible, competitive
3) reversible, non-competitive

32
Q

What happens during irreversible enzyme inhibition? Give an example of an irreversible enzyme inhibitor.

A

The molecule/drug binds very tightly, usually forming covalent bonds

Nerve gases e.g. Sarin

33
Q

What is common with all reversible enzyme inhibitors?

A

They don’t form covalent bonds and can freely dissociate

34
Q

What happens in reversible, competitive enzyme inhibition? What is the effect on Km and Vmax?

A

Molecule binds to active site.

Affects Km (increases) and not Vmax

35
Q

What happens in reversible, non-competitive enzyme inhibition? What is the effect on Km and Vmax?

A

Binds to another site on the enzyme

Affects Vmax (lowers) and not Km

36
Q

Why does competitive inhibition have no effect on Vmax?

A

Increasing the substrate concentration enough will always overcome the effect of the inhibitor - Vmax can still be reached

37
Q

How does a non-competitive enzyme inhibitor lower the Vmax?

A

Decreases the turnover number of the enzyme

38
Q

What reaction does creatine kinase catalyse?

A

Creatine + ATP —> Phosphocreatine + ADP

39
Q

Serum levels of creatine kinase are indicative of what?

A

Myocardial infarction if levels are high as it is released by damaged myocardial cells