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Phase 1 - S1 Medical Cell Biology And Genetics > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

What is the activation energy?

A

The minimum amount of energy required for a reaction to occur

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2
Q

Why are enzymes better for increasing the rate of a reaction rather than temperature and concentration

A

You want to maintain the temperature and concentration at a set point

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3
Q

What are enzymes?

A

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

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4
Q

Why don’t enzymes affect the reaction equilibrium

A

It catalysed the reaction equally forwards and backwards

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5
Q

What is the active site?

A

The place where substrates bind and the chemical reaction occurs

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6
Q

What is the lock and key hypothesis

A

Where active sites are complementary in shape to the substrate

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7
Q

What is the INDUCED fit hypothesis

A

Binding of substrates cause conformational changes in the enzyme

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8
Q

What type of bonds are formed between the active site and substrate?

A

Week hydrogen binds which hold the substrate in the correct orientation but also allows it to be released

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9
Q

What does the Michaelis-Menton model propose?

A

That a specific complex between the enzyme and the substrate is a necessary intermediate. Represents that the rate is related to concentration of substrate

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10
Q

What is Vmax

A

The maximal rate when all enzymes active sites are saturated with substrate

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11
Q

What is Km?

A

The substrate concentration that gives half maximal velocity

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12
Q

What does a low Km value tell you?

A

The enzyme has a high affinity for the substrate

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13
Q

What is the lineweaver-Burk plot

A

Reciprocal graph that gives -1/Km at the X intercept and 1/Vmax at the y intercept

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14
Q

What is an enzyme inhibitor?

A

Molecules that slow down or prevent an enzyme reaction

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15
Q

What are the 2 types of inhibitors?

A
  1. Irreversible - bind very tightly forming covalent bonds

2. Reversible - can freely dissociate as they don’t form covalent bonds

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16
Q

What are the 2 types of reversible inhibitors

A

1- competitive (binds to active site. Affects Km not Vmax)

2- Non-competitive (bind to another site in the enzyme. Affects Vmax not Km)

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17
Q

Why do competitive inhibitors not affect Vmax?

A

Adding enough substrate will overcome the affect of the inhibitor so the maximum rate can still be reached

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18
Q

Why do competitive inhibitors affect Km?

A

The inhibitor competes with the substrate for the active site so the affinity decreases

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19
Q

Why do competitive inhibitors lower Vmax?

A

They decrease the turnover rate of the enzyme

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20
Q

Why does the active site of an enzyme only occur a small area?

A

A large proportion of the enzyme is needed to hold the shape of the active site

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21
Q

What is the units of enzyme activity

A

Micromoles per minute per litre

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22
Q

What affect does doubling the enzyme concentration have on the rate

A

It doubles the rate of reaction

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23
Q

Why does enzyme activity stay the same despite changes the enzyme concentration

A

The enzymes always work to the same activity. The rate at which they work doesn’t not change.

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24
Q

What are the 2 long term regulation methods for enzymes

A
  1. Change in protein synthesis

2. Change in protein degradation

25
Q

What are the 2 short term regulation methods for enzymes

A
  1. Changes in substate/product concentration

2. Change in enzyme conformation

26
Q

State 3 ways in which enzyme conformation can be changed

A
  1. Allosteric regulation
  2. Covalent modification
  3. Proteolytic cleavage
27
Q

What graph shape do allosteric enzymes show

A

Sigmoidal

28
Q

Why do allosteric enzymes show a sigmoidal graph for rate vs substrate concentration.

A

As the enzyme can exist in 2 forms (T and R state)

29
Q

What do allosteric activators do

A

Increase the proportion of enzyme in the R state

30
Q

What direction do allosteric activators shift the binding curve

A

Left

31
Q

What do allosteric inhibitors do?

A

Increase proportion of enzyme in the T state

32
Q

Give an example of a Substance that allosteric ally activates phosphofructokinase

A

AMP

33
Q

Give a name of a substance that allosterically inhibits phosphofructokinase

A

ATP, citrate, H+

34
Q

Why can’t you work out Km from allosteric enzyme graphs

A

As it’s a sigmoidal relationship not Michaelis-Menton

35
Q

What enzymes add phosphates onto substances

A

Kinases

36
Q

What enzymes remove phosphate groups

A

Phosphatase

37
Q

Why is protein phosphorylation effective

A

Phosphate group can make Hydrogen bonds and the 2 negative charges on the group can cause a conformational change.

38
Q

What are zymogens

A

Inactive precursors of enzymes

39
Q

Where are zymogens synthesised

A

Stomach and pancreas

40
Q

What digestive enzyme activates lots of zymogens

A

Trypsin

41
Q

What condition results from a deficiency in alpha 1 antitrypsin

A

Emphysema

42
Q

What does alpha 1 antitrypsin do

A

Inhibits the actions of trypsin

43
Q

Why does a deficiency of alpha 1 antitrypsin cause emphysema

A

The trypsin activates elastase which breaks down the alveolar walls

44
Q

What are the 2 pathways of the blood clotting cascade

A

Intrinsic and extrinsic

45
Q

What does factor Xa do in the blood clotting cascade

A

Activates the zymogens prothrombin into thrombin

46
Q

What does thrombin do in the blood clotting cascade

A

Converts fibrotic into fibrin

47
Q

What does fibrin do in th blood clotting cascade

A

Cross links to form the blood clot

48
Q

What protein are Kringle domains found

A

Prothrombin

49
Q

What is the role of Kringle domains

A

Keep prothrombin in the inactive form

50
Q

How are Gla domains formed

A

The additions of COOH group to glutamate residues forming carboxyglutamate (Gla)

51
Q

What is the role of Gla domains

A

The negative charge of th Gla domains allows them to bind to the calcium ions at the site of damage and bring clotting factors together

52
Q

A defect in what factor causes haemophilia

A

8

53
Q

What does factor VIII do in the blood clotting cascade

A

Stimulates the activity of other factors

54
Q

What affect does protein C have in the blood clotting cascade

A

Degrades factors and so stops the clotting process

55
Q

What 3 methods stop the clotting process

A
  1. Dilution of clotting factors
  2. Digestion by proteases
  3. inhibitors
56
Q

What is fibrinolysis

A

Breaking down of a blood clot

57
Q

Why is vitamin K important in the blood clotting cascade

A

Required for the carboxylation of glutamate residues to form Gla domains.

58
Q

What inhibits the oxidisation of vitamin K

A

Warfarin

59
Q

How do zymogens become activated in acidic conditions

A

The pH causes a conformational change which unfolds the zymogen exposing the active site

Phase 1 - S1 Medical Cell Biology And Genetics (13 decks)

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