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BIOC192 > Lecture 9: WHY ARE ENZYMES ESSENTIAL FOR LIFE? > Flashcards

Lecture 9: WHY ARE ENZYMES ESSENTIAL FOR LIFE? Flashcards

1
Q

What are enzymes?

A

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

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2
Q

What are most enzymes?

A

Proteins

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3
Q

What are exceptions to proteins being enzymes?

A

Catalytic RNA’s, ribozymes including ribosomes

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4
Q

What don’t enzymes change?

A

The free energy level (equilibrium) of products and reactants

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5
Q

What is the relative abundance of products and reactants predicted by?

A

The Gibbs free energy

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6
Q

What happens when Gibbs free energy is less than 0?

A

There is energy released and the products dominate

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7
Q

What happens when the Gibbs free energy is greater than 0?

A

Energy is required and the reactants dominate

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8
Q

What happens when the Gibbs free energy is equal to 0?

A

The reaction is at equilibrium (reactants and products are of equal concentrations)

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9
Q

What does overall Gibbs free energy have components of?

A

Enthalpy (H) and entropy (S)

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10
Q

What is T?

A

Absolute temperature

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11
Q

What must happen to favour the forward reaction?

A

Either enthalpy must decrease or entropy must increase

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12
Q

What does cellular integrity mean?

A

A decrease in entropy (disorder) in the cell so energy from elsewhere is required

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13
Q

What do enzymes control?

A

Where and when energy is released to maintain the cell

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14
Q

What do reactions pass through?

A

High energy transition states

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15
Q

What determines the rate of a reaction?

A

The activation energy required to reach the transition state

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16
Q

What is the activation of the back reaction?

A

The Gibbs free energy + the activation energy

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17
Q

What does free energy do at equilibrium?

A

Sets the ratio of products to reactants

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18
Q

What is the Gibbs free energy for cleavage of DNA phosphodiester backbone?

A

Negative

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19
Q

How long is the DNA phosphodiester backbone stable for uncatalyzed?

A

Thousands of years

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20
Q

What is the speed of ribonuclease A?

A

Less than a millisecond

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21
Q

What does aldolase have?

A

Very positive Gibbs free energy but a big rate enhancement

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22
Q

What does adenylate kinase have?

A

Gibbs free energy near zero but a big rate enhancement

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23
Q

What are isozymes?

A

Enzymes which differ in amino acid sequence but catalyse the same reaction

24
Q

What are the classes of enzymes?

A

Oxireductases, transferases. hydrolyses, lyases, isomerases and ligases

25
Q

What are oxireductases involved in?

A

Redox (transfer of electrons)

26
Q

What are transferases involved in?

A

Transfer of a functional group

27
Q

What are Hydrolyses involved in?

A

Hydrolysis reactions (using water)

28
Q

What are lyases involved in?

A

Non-hydrolytic breaking or making of bonds (not using water)

29
Q

What are isomerases involved in?

A

Transfer of atoms/groups within a molecule to yield an isomeric form

30
Q

What are ligases involved in?

A

Joining two molecules together (forming a new bond) which is usually coupled to ATP cleavage

31
Q

What does muscle myosin do?

A

Use energy from hydrolysis of ATP (general energy store) to drive muscle contraction

32
Q

What does ATP synthase do?

A

Couple electrochemical gradient across the membrane to synthesise ATP

33
Q

Where does enzyme substrate binding occur?

A

At a specific site on the enzyme called the active site

34
Q

What does the active site have?

A

Amino acid side chains projecting into it

35
Q

What does the active site do?

A

Bind the substrate via several weak interactions

36
Q

What does the active site determine?

A

The specificity of the reaction

37
Q

What are the types of enzyme substrate bonds?

A

Ionic bonds/salt bridges, hydrogen bonds, van der Waals interactions and covalent bonds

38
Q

What do ionic bonds do?

A

Make use of charged side chains (Asp, Glu, Arg, Lys)

39
Q

What happens in hydrogen bonds?

A

Side chain or backbone O or N atoms can often act as hydrogen bond donors and acceptors (prevalent and give specificity)

40
Q

What are van der Waals interactions?

A

Between any protein and substrate atoms in close proximity (weakest interactions but abundant)

41
Q

What are covalent bonds?

A

Relatively rare and much stronger than the other bonds

42
Q

What are the models for enzyme substrate binding?

A

Lock and key and induced fit

43
Q

What is the lock and key model?

A

The shape of the substrate and the conformation of the active site are complementary to one another

44
Q

What is the induced fit model?

A

The enzyme undergoes a conformational change upon binding to substrate. The shapes of the active site becomes complementary to the shape of the substrate only after the substrate binds to the enzyme

45
Q

Are enzymes dynamic or static?

A

Dynamic

46
Q

What do many weak interactions ensure?

A

Specificity and reversibility

47
Q

How does enzyme substrate binding show specificity?

A

Several bonds are required for substrate binding

48
Q

When can weak bonds form?

A

Only if the relevant atoms are precisely positioned

49
Q

What can weak bonds allow?

A

reversible binding

50
Q

What is critical?

A

Molecular complementarity between enzyme and substrate

51
Q

What is optimal binding?

A

Not too tight

52
Q

How can activation energy be lowered?

A

By ground state destabilisation, transition state stabilisation and an alternate reaction pathway with a different (lower energy) transition state

53
Q

How can ground state destabilisation and transition state stabilisation occur?

A

By having an active site that has shape/charge complementarity to the transition state, not the substrate

54
Q

What are coenzymes?

A

Small organic molecules

55
Q

What type of substrates are coenzymes?

A

Cosubstrates

56
Q

What are cosubstrates carriers of?

A

Electrons, atoms or functional groups

57
Q

What are cofactors often derived from?

A

Vitamins

BIOC192 (38 decks)

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