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Biology A level > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

In general what do enzymes do?

A

Catalyse chemical reactions

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2
Q

What’s an anabolic reaction?

A

Building large polymers requiring enzymes, eg building cellulose for cell walls

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3
Q

What’s a catabolic reaction?

A

Breaking down large molecules, requires enzymes, eg. breaking down glucose in respiration to release energy

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4
Q

Definition of metabolism?

A

The sum of all different reactions or reaction pathways (multistep processes, each step catalysed by enzymes) in a cell or an organism

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5
Q

Examples of reactions which are enzyme controlled?

A

Hydrolysis, condensation, digestion

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6
Q

Name 3 metabolic processes enzymes are involved in?

A

Photosynthesis, respiration, protein synthesis

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7
Q

What are the enzymes called which break down peptide bonds?

A

Proteases

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8
Q

What are the substrates and products of catalase?

A

Substrate is hydrogen peroxide, product is Water and Oxygen

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9
Q

What are the substrates and products of amylase?

A

Substrates are large alpha linked polysaccharides such as starch and glycogen, products are glucose and maltose

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10
Q

What are the substrates and products of trypsin?

A

Substrate are proteins, products are polypeptides

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11
Q

4 key facts about enzymes?

A

They are globular proteins
They have active sites
They are specific
They are biological catalysts

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12
Q

Effect of enzymes being globular proteins?

A

They have tertiary structure, so can be denatured by heating and ph

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13
Q

Where does the substrate fit into they enzyme?

A

The active site in the tertiary structure, it’s shape is complementary

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14
Q

What happens if you heat an enzyme too much?

A 
Increase in thermal energy
Increase in kinetic energy
Molecules in bonds vibrate
Bonds break
Active site no longer fits substrate
Rate of reaction goes down
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15
Q

Why are enzymes called “specific”?

A

Only certain molecules fit into the active site

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16
Q

What does a catalyst do?

A

Covalently bonded molecules are too stable to fall apart easily, a catalyst gives the molecule enough energy for the bonds to break or form. The energy required to start a reaction is called activation energy

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17
Q

How do enzymes work as a catalyst?

A

Substrate molecules moving around all the time, but might not have enough activation energy for the reaction to start. So enzymes temporarily bind to the substrate, lowering the activation energy. (they aren’t used up in the reaction)

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18
Q

What does Vmax mean?

A

Maximum initial velocity/rate of enzyme controlled reaction

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19
Q

What’s a substrate?

A

Molecule the enzyme helps to react

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20
Q

What’s an enzyme-substrate-complex?

A

Formed when the substrate fits into the active site

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21
Q

What’s an enzyme?

A

Protein molecule that catalyses a metabolic reaction

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22
Q

What’s the product?

A

Formed by the reaction; released by the active site at the end of the reaction

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23
Q

Explain the lock and key hypothesis?

A

Substrate fits into the active site, as a key fits into a lock, because of their complementary shapes

The enzyme bonds to the substrate, and an enzyme substrate complex is formed

The product is released leaving the enzyme unchanged and ready for the next reaction

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24
Q

Why is the substrate held in the active site?

A

So the atom groups are close enough to react

The R groups of the active site interact with the substrate forming temporary bonds, putting a strain on the substrate helping the reaction along

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25
Q

What does induced fit hypothesis state?

A

That the active site changes shape as the enzyme substrate complex forms

The initial reactions between the active site and substrate are weak, they change the structure of the active site,

strengthening the binding with the substrate,

weakening particular bonds in it, lowering the activation energy

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26
Q

How does the transition state model add detail to induced fit hypothesis?

A

All reactions go through a transition state as the chemical compounds react with each other

The formation of the transition state determines the activation energy of the reaction

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27
Q

How do you find the rate of reaction?

A

Product divided by time

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28
Q

4 factors which affect the rate of reaction?

A

Substrate concentration
Enzyme concentration
Temperature
pH

29
Q

How does substrate concentration affect the rate of reaction?

A

If there are more substrate molecules per unit volume, then there is more chance they will collide with an enzyme per unit time

So more enzyme substrate complexes will form per unit time

More product will form per unit time

Rate of reaction will increase

30
Q

What’s the point of saturation?

A

Where increasing that factor anymore won’t increase the rate of reaction

31
Q

What’s a limiting factor?

A

When that factor can still be altered to increase the rate of reaction

32
Q

How does enzyme concentration effect the rate of reaction?

A

If substrate is continually added, then as enzyme concentration increases, so does the rate of reaction

33
Q

How does the temperature affect the rate of reaction?

A

As thermal energy increases, so does kinetic energy

Molecules move faster and collision are more likely to occur between enzyme and substrate

But enzymes are proteins so if the temperature becomes too high they denature and the rate of reaction decreases

34
Q

How does pH affect the rate of reaction?

A

Change in pH can change the shape of the enzyme, which effects the enzymes activity

Most enzymes work in narrow range of pH, as slight change will decrease rate of reaction. However enzymes won’t be denatured by a slight pH change, as they can reform

Also the H+ concentration will change, which in turn will cause changes to the interactions between the R groups in the active site and the substrate

35
Q

What is used in a reaction to prevent the pH from changing?

A

pH buffers

36
Q

What is pH?

A

The measure of concentration of H+ ions in a solution

37
Q

Location and optimum pH of pepsin?

A

Stomach, pH2

38
Q

Location and optimum pH of trypsin?

A

Small intestine, pH7

39
Q

What do competitive inhibitors do?

A

Bind to the same site as the substrate, preventing the substrate from binding, but are not changed by the enzyme

So the competitive inhibitors have a similar shape to the substrate,
So the active site is blocked
Substrate cannot enter the active site
An enzyme-inhibitors is formed
No product is made
40
Q

How can you override the effects of a competitive inhibitor?

A

Increase substrate concentration quickly, blocks all the active sites first

41
Q

How does statin work?

A

It’s a competitive inhibitor of an enzyme used in cholesterol synthesis, so it reduces the amount of cholesterol

42
Q

How does asprin work?

A

Irreversibly inhibits the active site of COX enzymes, preventing the synthesis of prostaglandins and thromboxane, the chemicals responsible for producing pain and fever

43
Q

How do non competitive inhibitors work?

A

Bind to some other site on the enzyme, altering the tertiary structure and shape of the active site

So allosteric bonding
Tertiary structure altered
Active site altered
Substrate no longer fits active site
No ESC formed
No product formed
44
Q

What’s end product inhibition?

A

When the end product of a pathway acts as an inhibitor for the whole pathway, example of negative feedback

45
Q

What’s a cofactor?

A

The non protein part of an enzyme

46
Q

How do cofactors activate enzymes?

A

Binding loosely to them

47
Q

How do cofactors help enzymes to carry out their function?

A

Transfer atoms or groups from one reaction to another in a metabolic pathway

48
Q

What are inorganic cofactors?

A

Taken in in the diet as minerals, include zinc, iron, calcium and chloride IONS

49
Q

Example of inorganic enzyme helping?

A

Amylase breaks down starch to maltose, a chloride ion helps form the correct shape of the active site

50
Q

What’s a coenzyme?

A

Mostly derived from vitamins, eg. Vitamin B3 is used to synthesise NAD

51
Q

What does NAD do?

A

Transfers hydrogen atoms between molecules in the reactions in respiration

52
Q

Which coenzyme does vitamin B5 make?

A

coenzyme A, which is essential in the breakdown of carbohydrates and fatty acids in respiration

53
Q

What’s a prosthetic group?

A

Required by certain enzymes to carry out their function, permanently and tightly bound to the enzyme

54
Q

Example of a prosthetic group?

A

Carbonic anhydrase, involved in the metabolism of carbon dioxide, it has a Zn+ ion forming an important part of it’s structure

55
Q

What’s an enzyme in it’s inactive form called?

A

apoenzyme

56
Q

What’s a precursor enzyme?

A

Enzyme which needs to be activated

57
Q

How is a precursor enzyme activated?

A

Adding a cofactor, which changes the tertiary structure

58
Q

What’s an activated enzyme called?

A

holoenzyme

59
Q

What does alcohol dehydrogenase need to work?

A

NAD+ to accept hydrogen in the conversion of ethanol to ethanal

60
Q

Example of an enzyme helping activate another enzyme?

A

Protease enzyme activates another enzyme by chopping through bonds

61
Q

Why can temp of pH activate an enzyme?

A

because they can change the tertiary structure

62
Q

Example of pH activating an enzyme?

A

The enzyme in it’s inactive form is called a zymogen or proenzyme, which is activated into pepsin (active form), when the stomach turns acidic due to pepsinogen being released into the stomach to digest protein

63
Q

What’s the allosteric site?

A

Where non competitive enzymes bind on to the enzyme

64
Q

What’s the temperature coefficient of a reaction?

A

The amount the reaction increases for every 10 degrees increase, (about x2 in enzymes)

65
Q

What are intracellular enzymes?

A

Enzymes that act within the cell

66
Q

Example of an intracellular enzyme?

A

The enzyme catalase breaks down the toxic hydrogen peroxide which is a product of many metabolic pathways into oxygen and water within the cells

67
Q

What are extracellular enzymes?

A

Enzymes which are released from cells to break down large nutrient molecules, into smaller molecules for digestion, they work outside the cell, or out of the body in fungi’s case

68
Q

Describe the digestion of starch (extracellular enzymes)?

A

Starch polymers partially broken down into maltose (disaccharide).
The enzyme involved in this stage is amylase, which is produced by saliva glands and the pancreas, and released into the mouth (saliva) and the small intestine (pancreatic juice)
Maltose is then broken down into glucose, which is a monosaccharide, the enzyme involved in this stage is called maltase, as is present in the small intestine.
Glucose is small enough to be absorbed by cells lining digestive system

69
Q

Describe the digestion of protein (extracellular enzymes)

A

Trypsin is a protease, a type of enzyme which catalyses the digestion of proteins into smaller peptides, which can be broken down into amino acids by further proteases. Trypsin is produced by pancreas and released into pancreatic juice in small intestine, amino acids then absorbed by cells lining digestive system and go into the blood stream

Biology A level (19 decks)

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