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Enzymes > Enzymes 1 > Flashcards

Enzymes 1 Flashcards

1
Q

What is an enzyme?

A

A globular protein

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2
Q

How does a biological catalyst differ from a chemical catalyst?

A

Catalyses very high reaction rates
Shows great reaction specificity
Work in mild temperature/pH conditions
Can be regulated

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3
Q

What is a ribozyme?

A

Catalytic RNA molecules with no protein component

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4
Q

What is a cofactor?

A

Non-protein component needed for activity

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5
Q

What is a coenzyme?

A

Complex organic molecule, usually produced from a vitamin

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6
Q

What is a prosthetic group?

A

Cofactor covalently bound to the enzyme or very tightly associated with the enzyme

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7
Q

What is an apoenzyme?

A

The protein component of an enzyme that contains a cofactor.

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8
Q

What is a haloenzyme?

A

The apoenzyme plus the cofactor(s) “whole enzyme”

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9
Q

What is a substrate?

A

Molecule acted on by the enzyme

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10
Q

What is the active site?

A

Part of the enzyme in which the substrate binds and is acted upon.

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11
Q

What are the 6 classes of enzymes?

A 
Oxidoreductases
Transferases
Hydrolases
Lysases
Isomerases
Ligases
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12
Q

What do oxidoreductases do?

A

Transfer e

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13
Q

What do transferases do?

A

Group transfers

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14
Q

What do hydrolases do?

A

Hydrolysis (transfer chemical groups to water)

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15
Q

What do lyases do?

A

Form, or add groups to double bonds

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16
Q

What do isomerases do?

A

Transfer groups within molecules (form isomers)

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17
Q

What do ligases do?

A

Formation of C-C, C-S, C-O, C-N bonds (coupled to ATP cleavage)

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18
Q

What do enzymes not do?

A

Move reaction equilibria

Make a non-spontaneous reaction spontaneous

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19
Q

What do enzyme do?

A

Increase rates of spontaneous reactions
Lower the activation energy of biochemical reactions
Accelerate movement towards reaction equilibrium

20
Q

What is Gibbs Free-Energy?

A

“Useful” energy generated from cellular reactions

21
Q

Why must spontaneous reactions have a -ve deltaG value.

A

They will decrease enthalpy and/or increase entropy

22
Q

Why are spontaneous reactions not instantaneous?

A

Due to the energy barrier

23
Q

What is the energy barrier?

A

The energy required to position chemical groups correctly, bond rearrangements, e arrangements etc.

24
Q

What does the transition state show?

A

The moment that the chemical bonds are formed and broken

25
Q

What can happen once a reaction has reached transition state?

A

Reactions can then go wither way- revert back to S or change to P

26
Q

What is the binding energy?

A

When enzymes form non-covalent bonds with substrate molecules allowing them to take the reaction through a different path of reaction intermediates.

27
Q

When is a small amount of energy required?

A

To get past transition state.
To get components to bind together
To release products from cell.

28
Q

What does the active site have to be complementary to for a reaction to take place?

A

The transition state

29
Q

How do enzymes reduce activation energy?

A

Entropy reduction
Desolvation
Inducced fit

30
Q

What happens in entropy reduction?

A

Molecules in free solution will only react by bumping into one another
Enzymes force the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed.

31
Q

What is desolvation?

A

Weak bonds between the substrate and enzymes essentially replace most or all of the H-bonds between substrate and aqueous solution

32
Q

What is induced fit?

A

Conformational changes occur in the protein structure when the substrate binds

33
Q

How can we analyse an enzyme?

A

Enzyme kinetics
Mutagenesis
3D structure

34
Q

How can enzyme kinetics be measured?

A

Changing substrate concentration would change the initial rate of a reaction.
More substrate= higher initial rate of reaction
As the reaction proceeds the substrate is used up and the rate of reaction changes.
Initial velocity can be studied if we assume that initial [S] does not change.

35
Q

What response is shown when there is an increase in [S] at low [S]?

A

Almost linear increase in Vo when graphed

36
Q

What response is shown when there is an increase in [S] at high [S]?

A

Very little response in Vo

37
Q

Why is there very little response when [S] is increased at high [S]?

A

Vmax (maximum velocity) occurs because all of the enzyme active sites are saturated with substrate.

38
Q

What does the Michaelis-Menten equation state?

A

The first part of the reaction (to produce ES) occurs reversibly
The second part of the reaction (to produce E and P) occurs more slowly than the first part

39
Q

What assumptions are made about the Michaelis-Menten equation?

A

If 2nd part is slower it must limit the rate of the overall reaction so the overall rate of reaction must be proportional to the amount of ES
More ES would give a higher overall reaction rate and less would give slower overall reaction rate

40
Q

How is the Michaelis constant calculated?

A

From the hyperbolic reaction curve as half of the Vmax?

41
Q

What is the M-M equation?

A

Vo= Vmax[S]
————
Km+[S]

42
Q

What is Km?

A

Km is equivalent to the substrates concentration at which the initial reaction rate is half of the maximum reaction rate.

43
Q

What do larger Km values indicate?

A

A less stable ES complex

44
Q

What do smaller Km values indicate?

A

A more stable ES complex.

45
Q

What does Vmax tell you?

A

How fast a reaction is proceeding when the enzyme is saturated with substrate.
A measure od the enzymes catalytic rate

46
Q

Why would the Km or Vmax value differ for the same enzyme?

A

It may function differently in different cells.

Enzymes (1 decks)

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