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BDS1 Molecules and Cells > Enzymes > Flashcards

Enzymes Flashcards

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Organic Chemistry 101 flashcards
1
Q

What are enzymes?

A

Catalysts that speed up chemical reactions

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2
Q

Do enzymes alter the equilibrium of a reaction?

A

No, but they do accelerate the time it takes to reach equilibrium

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3
Q

What are a few roles of enzymes in living organisms?

A

Aid:

  • respiration
  • digestion
  • Muscles and nerve function
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4
Q

What is the role of Alkaline phosphatase?

A

Found throughout the body, involved in mineralisation of tissue and bone

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5
Q

What is the role of Amylase?

A

Found in saliva, converts starch into sugars

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6
Q

What is the role of Maltase?

A

Found in saliva, breaks maltose into glucose

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7
Q

What is the role of Lysozyme?

A

Antimicrobial, breaks down peptidoglycan layer in bacterial cell wall’s

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8
Q

What is the enzymes ‘lock and key’ model?

A

Enzymes active site complimentary in shape to that of a specific substrate

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9
Q

What is the enzymes ‘indices-fit’ model?

A
  • When the active site and substrate do not fit together exactly but the enzyme changes shape when the substrate binds to become a complimentary shape to the substrate
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10
Q

What does Sucrase break down into?

A

Glucose and Fructose

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11
Q

What are most enzymes made of?

A

Protein

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12
Q

What is enzyme activity dependent on?

A

The maintenance of their 3D structure

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13
Q

What is enzyme activity affected by?

A

Temperature and pH

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14
Q

What happens to enzymes at extremes of temperature or pH?

A

They will denature and become totally inactive

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15
Q

What is the difference between energies of reactants and products called?

A

Standard free energy change

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16
Q

What is the energy input required to initiate a reaction called?

A

The activation energy

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17
Q

Is activation energy higher or lower for a catalysed reaction compared to an uncatalyzed reaction?

A

Lower

18
Q

Can enzymes alter the free energy change?

A

No

19
Q

What 6 factors affect the rate of an enzyme reaction?

A
  1. Temperature
  2. pH
  3. Enzyme concentration
  4. Substrate concentration
  5. Inhibitors and activators
  6. Covalent modification (the alteration of a synthesised protein facilitated by a catalyst)
20
Q

What is Thermodynamic activation?

A

Increase in free energy

21
Q

What is Thermodynamic inactivation?

A

Protein denaturation - enzyme rapidly loses activity

22
Q

What effect will an increase in the enzyme concentration have on the reaction rate?

A

Will increase the reaction rate:
- more enzymes = faster reaction
so the equilibrium will be reached more rapidly

23
Q

Once equilibrium is reached in a reaction what will happen to the concentrations of the product and substrate?

A

They will not change

24
Q

What is Vmax?

A

The maximum rate of reaction (enzyme is saturated with substrate)

25
Q

What is Km?

A

The Michaelis constant, an inverse measurement of affinity - the higher the Km value, the lower the affinity of the enzyme for its substrate
The Km is the concentration of substrate at which the rate of reaction is half its maximum value

26
Q

What does a low Km indicate?

A

The enzyme is normally saturated with substrate, acts at a fairly constant rate regardless of variations in substrate concentration

27
Q

What does a high Km indicate?

A

The enzyme is not normally saturated with substrate, its activity will vary as substrate concentration varies - rate of product formation depends on substrate availability

28
Q

What is the Michaelis-Menten equation?

A

V = Vmax[S]/(Km + [S])

  • Km is the substrate concentration at which V = 0.5Vmax and is a measure of the affinity of the enzyme for its substrate: the lower the Km, the higher the affinity
  • Vmax and hence Km can be estimated from the graph of V against [S]
29
Q

What is the Lineweaver-Burk plot?

A

A more accurate estimate of Vmax and Km by plotting 1/V and 1/[S] - gives a straight line for most enzymes

30
Q

What is an irreversible inhibitor?

A
  • damages enzymes beyond repair

- Completely inactivates permanently

31
Q

What is a reversible inhibitor?

A
  • full enzyme activity is regained when the inhibitor is removed
  • Most natural enzyme inhibitors fall into this category
32
Q

What is feedback inhibition?

A

A product of a pathway acting as an inhibitor of an earlier step in the pathway

33
Q

What is a competitive inhibitor?

A
  • Where a substrate and inhibitor compete for the same active binding site
  • Inhibition can be overcome with large quantities of substrate
34
Q

What is a non-competitive inhibitor?

A
  • Binds to an allosteric site on the enzyme i.e. one other than the active site
  • Inhibition cannot be reversed by adding large quantities of substrate
35
Q

Do competitive inhibitors alter the Vmax of an enzyme?

A

No, as a large quantity of substrate can outcompete the inhibitor

36
Q

Do competitive inhibitors alter the Km of an enzyme?

A

Yes, the Km is increase, as inhibitor competes with substrate for binding to active site, affinity of substrate will appear to decrease (Km is an inverse measure of affinity)

37
Q

Do non-competitive inhibitors alter the Vmax of an enzyme?

A

Yes, Vmax is decreased, a proportion of the enzyme molecules will be inactive at any time due to binding by the inhibitor

38
Q

Do non-competitive inhibitors alter the Km of an enzyme?

A

No, Km is unchanged as binding of a substrate can still occur

39
Q

What are allosteric enzymes?

A

In addition to active sites they also possess allosteric sites to which non-substrate modulators bind, creating a conformational change in subunits

40
Q

What do positive modulators do?

A

Increase the affinity for substrate at active site

41
Q

What do negative modulators do?

A

Decrease the affinity for substrate at active site

42
Q

Many enzymes can be covalently modified by other enzymes to modify their activity. What is a common modification?

A

The addition of a phosphate group

  • The enzyme which brings this about is phosphorylase kinase, which in turn is activated indirectly by adrenaline and glucagon
  • The effect is reversed by phosphorylase phosphatase, which removes the phosphate group

BDS1 Molecules and Cells (14 decks)

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