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BIOLOGY (OCR A-LEVEL) > CHAPTER 4 - ENZYMES > Flashcards

CHAPTER 4 - ENZYMES Flashcards

1
Q

What is an enzyme?

A

A biological catalyst ( speeds up metabolic reactions and doesn’t get used up)

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2
Q

What is an anabolic enzyme reaction?

A

Building up molecules - requires energy

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3
Q

What is a catabolic enzyme reaction?

A

Breaking down large molecules - releases energy

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4
Q

What is the lock and key model?

A

The substrate is already complimentary to the active site of the enzyme.

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5
Q

What is the induced-fit hypothesis?

A

The active site of enzyme changes shape slightly as substrate enters.

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6
Q

Name 1 intracellular (works inside the cell) enzyme

A

Catalase

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7
Q

Name 3 extracellular (works outside the cell) enzymes

A

Amylase
Maltase
Trypsin

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8
Q

State 2 features of catalase

A
  • found in all organisms exposed to oxygen

- catalyses decomposition of hydrogen peroxide (by product of many metabolic reactions/harmful) to water and oxygen

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9
Q

What does amylase do?

A

Works in saliva to catalyse hydrolysis of starch into maltose

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10
Q

What does maltase do?

A

Works in small intestine to catalyse hydrolysis of maltose into glucose

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11
Q

What does trypsin do?

A

Catalyses hydrolysis of peptide bonds of large polypeptides into smaller ones

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12
Q

What are the 2 steps of starch digestion?

A
  1. Amylase partially breaks down starch polymers into maltose
  2. Maltase breaks down maltose into glucose
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13
Q

What is trypsin also known as?

A

Protease

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14
Q

Where is trypsin produced and released?

A

Produced in pancreas/ released into small intestine

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15
Q

What is the digestion of protein?

A

Polypeptides broken down into amino acids by protease. Absorbed by cell lining in the digestive system and then absorbed into bloodstream.

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16
Q

What happens to enzyme reactions when temp increased?

A
  • more kinetic energy
  • more collisions
  • more successful collisions between enzyme and substrate
  • increase rate of reaction
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17
Q

Define temperature coefficient (Q10)

A

measure of how much rate of reaction increase with 10 degree rise in temp

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18
Q

How do you calculate Q10

A

rate at higher temp
—————————
rate at lower temp

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19
Q

What happens to the enzyme when temp is increased too much?

A
  • vibrations increase and bonds strain till broken
  • tertiary structure changes (denatured)
  • active site shape no longer complimentary to substrate
  • enzyme no longer functions
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20
Q

What is optimum temperature?

A

Temp at which enzyme has highest rate of activity

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21
Q

Optimum temp of human body?

A

40

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22
Q

Optimum temp of thermophilic bacteria (hot)

A

70

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23
Q

Optimum temp of psychrophilic organisms (cold)

A

5

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24
Q

What happens to rate of reaction above optimum temp?

A

Decreases rapidly

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25
What happens to rate of reaction below optimum temp?
Still present but less rapid
26
Features of enzymes in cold environments.
- more flexible structure (particularly at active site) - less stable than enzymes working at high temps - small temp change will denature them
27
Features of enzymes in hot environments.
- more stable (increased h bonds and disulphide bonds in tertiary) - shape and active site of enzyme more resistant to temp change
28
What is optimum pH?
A narrow range where the enzyme will function.
29
What happens when pH is altered slightly?
Structure of enzyme and active site is altered slightly
30
What happens when pH returns to optimum?
Renaturation: enzyme resumes its normal shapes and catalyses reactions
31
What happens when pH significantly changed?
Structure of enzyme irreversibly altered/ active site no longer complimentary to substrate.
32
What does amylase catalyse?
Starch ——> maltose
33
What does pepsin and trypsin catalyse?
Proteins ——> polypeptides
34
What does lipase catalyse?
Triglycerides——> glycerol + fatty acids
35
What does Maltase catalyse?
Maltose ——> glucose
36
What happens when substrate conc increases?
- higher collision rate with enzyme active sites - more enzyme-substrate complexes formed - rate of reaction increases
37
What happens when conc of enzyme increases?
- more active sites available | - enzyme-substrate complexes formed at a faster rate
38
Define concentration
Number of molecules per unit volume
39
Define Vmax
Maximum rate enzyme is working at
40
How do you calculate the rate of reaction? (cm3s-1)
1. Draw tangent from 0 2. Calculate gradient: change in y —————— change in x
41
What is competitive inhibition?
A competitive inhibitor binds to active site of enzyme and blocks the substrate from binding.
42
How does competitive inhibition effect the rate of reaction?
- reduces rate for given conc of substrate , Vmax doesn’t change for enzyme it inhibits - substrate conc increased, more substrate then inhibitor, Vmax can still be reached
43
State 2 examples of competitive inhibition.
- statins inhibit enzyme for synthesis of cholesterol to help reduce blood cholesterol conc - aspirin irreversibly inhibits cox enzyme - prevents synthesis of prostaglandins and thromboxanxe (chemicals causing pain and fever)
44
What is non-competitive inhibition?
A non-competitive inhibitor binds to the allosteric site of an enzyme which cause tertiary structure and active site to change shape so substrate is no longer complimentary and cannot bind.
45
How does non-competitive inhibition effect the rate of reaction?
- increase conc of enzyme or substrate does not overcome effect on NC inhibitor - increasing conc of NC inhibitor further decreases rate, less active sites available
46
What are 2 examples of irreversible non-competitive inhibitors?
- organophosphate (insecticides and herbicides) inhibit enzyme acetyl cholinesterase (nerve impulse transmission) — leads to muscle cramps, paralysis, death if ingested - proton-pump inhibitor treats long term indigestion. Blocks enzyme system from secreting H ions into stomach - can lead to formation of stomach ulcers
47
When does end-product inhibition occur?
When product of enzyme controlled reaction acts as inhibitor to enzyme that produces it ( negative feedback control mechanism for a reaction)
48
How does ATP regulate its own production?
PFK competitively inhibits ATP
49
What happens at high ATP levels?
- ATP bond to allosteric site of PFK - prevents addition of second phosphate to glucose - glucose not broken down - ATP not produced at same rate
50
What happens at low levels of ATP?
- less ATP binds to PFK - enzyme can catalyse addition of second phosphate to glucose - respiration resumes - more ATP produced
51
What is a cofactor?
Non-protein substance that helps the enzyme to work (makes up part of active site or binds to allosteric site to alter tertiary and active site so substrate can bind)
52
What do inorganic cofactors do?
- help enzyme and substrate bind | - does not participate in reaction
53
Examples of inorganic cofactors.
- minerals in diet | - chloride ions cofactors for amylase enzyme
54
What do coenzymes (organic cofactors) do?
Act as carriers moving chemical groups between enzymes. - participate in reaction and changed slightly - continually recycled during process
55
Example of coenzyme
Vitamins
56
Example of coenzyme
Vitamins
57
What is a prosthetic group?
A cofactors that is tightly bound to an enzyme
58
Example of prosthetic group.
- zinc ions are prosthetic group for carbonic anhydrase - zinc ion becomes permanent part of enzymes active site - carbonic anhydrase important for metabolism of carbon dioxide
59
What is precursor activation?
Enzymes produced in inactive form (so doesn’t damage cell where it’s synthesised and to control enzyme activity) and needs a cofactor to bind to activate it
60
What is an apoenzyme?
Precursor inactive protein ( no factor added)
61
What is a holoenzyme?
Active form of enzyme (cofactor added)
62
What is a zymogen?
An inactive precursor enzyme that requires covalent modification usually by another enzyme.
63
What are 2 examples of zymogens?
1. Trypsinogen (inactive) : another enzyme changes covalent bonding to make it trypsin 2. Pepsinogen (inactive): extreme stomach pH changes covalent bonding to make it active pepsin

BIOLOGY (OCR A-LEVEL) (9 decks)

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