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Science for Medicine > Enzymes 1 > Flashcards

Enzymes 1 Flashcards

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1
Q

What is an enzyme?

A
  • Globular protein

- Biological catalyst

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2
Q

What does an enzyme do?

A
  • Catalyses very high reaction rates
  • Shows great reaction specificity
  • Work in mild temp/pH conditions
  • Can be regulated
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3
Q

Ribozyme

A

Catalytic RNA molecule with no protein component

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4
Q

Cofactor

A

Non-protein component needed for activity

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5
Q

Coenzyme

A

Complex organic molecule, usually produced from a vitamin

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6
Q

Prosthetic group

A

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

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7
Q

Apoenzyme

A

The protein component of an enzyme that contains a cofactor

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8
Q

Holoenzyme

A

The apoenzyme plus the cofactor(s)

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9
Q

Substrate

A

Molecule acted on by the enzyme

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10
Q

Active Site

A

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

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11
Q

Class 1

Oxidoreductases

A

Transfers e

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12
Q

Class 2

Transferases

A

Group transfers

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13
Q

Class 3

Hydrolases

A

Hydrolysis

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14
Q

Class 4

Lyases

A

Form, or add groups to double bonds

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15
Q

Class 5

Isomerases

A

Transfer groups within molecules

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16
Q

Class 6

Ligases

A

Formation of C-C, C-S, C-O, and C-N bonds

17
Q

What do enzymes not do?

A
  • Move reaction equilibria

- Make a non-spontaneous reaction spontaneous

18
Q

What can enzymes do?

A
  • Increase rate of spontaneous reaction
  • Lower the activation energy of biochemical reactions
  • Accelerate movement towards reaction equilibrium
19
Q

What is Gibbs free energy?

A

Useful energy generated from cellular reactions

20
Q

What is true of spontaneous reactions?

A

They must have -ve ΔG value as they will decrease enthalpy and/or increase entropy

21
Q

What is the energy barrier equal to?

A

Energy required to position chemical groups correctly

22
Q

What does the transition state represent?

A

The moment that chemical bonds are formed and broken

23
Q

Binding energy

A

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

24
Q

What must the active site be complementary to in order for a reaction to take place?

A

Transition state

25
Q

What 3 ways do enzymes reduce activation energy?

A
  • Entropy reduction
  • Desolvation
  • Induced fit
26
Q

How does entropy reduction reduce activation energy?

A
  • Molecules in free solution will only react by bumping into one another
  • Enzymes force the substrate to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
27
Q

How does desolvation reduce activation energy?

A

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

28
Q

How does induced fit reduce activation energy?

A

Conformational changes occur in the protein structure when the substrate binds

29
Q

How can an enzyme by analysed?

A
  • Enzyme kinetics
  • Mutagenesis
  • 3D structure
30
Q

Why does Vmax occur when you increase the amount of substrate?

A

All of the enzyme active sites are saturated with substrate

31
Q

What is critical to the Michaelis-Menten equation?

A

Formation of an enzyme-substrate complex

32
Q

What does the model state?

A
  • The first part of the reaction (to produce ES) occurs reversibly
  • Second part of the equation (to produce E and P) occurs more slowly than the first part
33
Q

What assumptions are made with 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 a slower overall reaction rate
34
Q

What is the M-M equation?

A

Vo= Vmax[S]
————
Km+ [S]

35
Q

What is the M-M equation consistent with?

A

The experimentally observed dependence of Vo on [S] with the curves shape depending on Vmax/Km at low [S] and depeding on Vmax at high [S]

36
Q

Define Km.

A

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

37
Q

What do larger Km values indicate?

A

A less stable ES complex

38
Q

What do smaller Km values indicate?

A

A more stable ES complex

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