2.4.2 cofactors

Question 1

cofactor

Answer 1

substance that must be present to ensure an enzyme-catalysed reaction occurs at the appropriate rate (different types)

Question 2

which cofactors are part of the enzyme structure

Answer 2

prosthetic groups

Question 3

which cofactors form temporary associations with the enzyme

Answer 3

• mineral ion cofactors
• organic coenzymes

Question 4

enzyme-substrate complex

Answer 4

complex formed by temporary binding of enzyme & substrate molecules during enzyme-catalysed reaction

Question 5

describe prosthetic groups

Answer 5

• permanently bound by covalent bonds
• eg. carbonic anhydrase & zinc ion (prosthetic group) bound to active site

Question 6

explain how the zinc ion (prosthetic group) supports carbonic anhydrase
- where’s the enzyme found
- what does it catalyse
- why’s it important

Answer 6

• carbonic anhydrase found in erythrocytes
• catalyses interconversion of carbon dioxide & water to carbonic acid —> breaks down to protons & hydrogencarbonate ions
• reaction may proceed in both directions (depends on conc. of substrate/product molecules)
• important reaction as allows carbon dioxide and to be carried in blood from respiring tissues to lungs

Question 7

describe (mineral ion) cofactors & use an example
- what do they do
- 2 different types & explain
- example of cofactor

Answer 7

• temporarily bind (substrate/enzyme) to allow easier formation of ESC & increase rate of enzyme-catlysed reaction
• some act as co-substrates: they & substrate form complementary shape to bind to active site
• other change the charge distribution on the surface of the substrate/active site: make temporary bonds in ESC easier to form
• eg. amylase digests starch to maltose & requires chloride ions

Question 8

describe coenzymes

Answer 8

• small organic non-protein molecules
• bind temporarily to active site of enzyme either just before/at same time as substrate binds
• chemically changed during
• need to be recycled to original state (often by different enzyme)

Question 9

where are many co-enzymes derived from & what happens if these vitamins are deficient in humans diet

Answer 9

water-soluble vitamins
- disease may result

Question 10

B12: coenzyme derived from it & human deficiency disease

Answer 10

1. cobalamin coenzymes
2. pernicious anaemia - progressive/fatal anaemia

Question 11

folic acid: coenzyme derived from it & human deficiency disease

Answer 11

1. tetrahydrofolate
2. megablastic anaemia (large/irregularly shaped erythrocytes)

Question 12

nicotinamide, B3: coenzyme derived from it & human deficiency disease

Answer 12

1. NAD, NADP
2. pellagra (diarrhoea, dermatitis & dementia)

Question 13

pantothenate, B6: coenzyme derived from it & human deficiency disease

Answer 13

1. coenzyme A
2. elevated blood-plasma triglyceride levels

Question 14

thiamine, B1: coenzyme derived from it & human deficiency disease

Answer 14

1. thiamine pyrophosphate
2. beriberi (mental confusion, irregular heartbeat, muscular weakness, paralysis & heart failure)

Question 15

reaction for catalysing of carbonic anhydrase

Answer 15

CO2 + H2O <-—-> H2CO3 <—> H+ + HCO3-