Chapter 4 - Enzymes

Question 1

What are enzymes ?

Answer 1

Enzymes are globular proteins that interact with substances causing them to react faster.

Question 2

Why are enzymes used to catalyse reactions ?

Answer 2

• Using other factors such as pH or temp would damage living cells

Question 3

What are enzymes used for ?

Answer 3

• Speed up anabolic reactions used for growth
• Speed up catabolic reactions

Question 4

What are the two main types of enzymes ?

Answer 4

1) Intracellular enzymes
- Enzymes that work within cells used to carry out catabolic reactions
2) Extra cellular enzyme s
- Enzymes secreted by cells to break down large nutrients that cannot fit into the organism

Question 5

What is an example of intracellular enzymes ?

Answer 5

• Catalase = Breaks down H2O2 into O2 and H2O

Question 6

What are two examples of extra celllular enzymes ?

Answer 6

• Amylase = secreted in saliva, hydrolises glycosidic bonds in maltose
• Trypisin = made in pancrease, works in small intestine to hydrolise peptide bonds in proteins to soluble amino acids absorbed into the blood

Question 7

What are the two models for how enzymes work ?

Answer 7

1) Lock and Key model
2) Induced fit model

Question 8

What does the lock and key model state ?

Answer 8

• Within tertiary structure there are complementary active sites
• Enzymes bind to substrates creating enzyme-substrate complexes
• R-groups within active sites interact which causes strains
• Enzyme product complex is then formed

Question 9

What does the induced fit model state ?

Answer 9

• Active site changes to fit the substrate
• Initial interactions between enzyme and substrate causes weak bonds to form
• changes tertiary structure of enzyme which strengthens binding and puts strains on molecules

Question 10

What factors affect enzyme activity ?

Answer 10

1) Temperature
2) pH
3) Enzyme-substrate conc.

Question 11

How does temperature affect enzyme activity ?

Answer 11

• Increase temp = increase kinetic energy = increase in successful collisions = increased ROR
• However in high temperatures bonds in proteins vibrate vigorously until they break causing denaturing

Question 12

How does pH affect enzyme activity ?

Answer 12

The tertiary structure of an enzyme is dependant on hydrogen and ionic bonds between amino acids, above and below optimum causes changes in these bonds due to a decrease or increase in H+ conc. Thereby changed active site shape (This is reversible)

Question 13

How does enzyme-substrate conc. affect enzyme activity ?

Answer 13

Increase in emzyme or substrate conc. = increase in successful collisions = increase in ROR

Question 14

What are enzyme inhibitors ?

Answer 14

Inihibitors are molecules that prevent enzymes from carrying out their function or slows them down

Question 15

What are the two types of inhibitors ?

Answer 15

1) Competitive
2) Non-competitive

Question 16

How do competitive inhibitors work ?

Answer 16

• Molecule that has a complementary shape to the enzymes active site and binds to it
• Reduces no. enzymes that can form complexes thereby reducing ROR
• Temprorary

Question 17

How do non-competitive inhibitors work ?

Answer 17

• Inhibits and binds to allosteric sites of enzymes
• This changes tertiary structure of the enzyme; no longer has a complementary shape
• An increase in enzyme or substrate conc. would not increase ROR

Question 18

How is Vmax affected by the presence of these inhibitors ?

Answer 18

Question 19

What is end product inhibition ?

Answer 19

• The product of a reaction acts as an inhibtor to the enzyme that produces it

Question 20

What is an example of end product inhibition

Answer 20

Respiration
- Results in the prodcution of ATP, When glycolysis is carried out the addition of 2 phosphate groups are catalsed by PFK - ATP competitively inhibits this enzyme therefore regulates its own production

Question 21

What are cofactors ?

Answer 21

• non-protein helper components used to help enzymes carry out their functions as biological catalysts

Question 22

What are coenzymes ?

Answer 22

• Organic cofactors

Question 23

What are prosthetic groups ?

Answer 23

• Cofactors that are required by certain enzymes to carryout their catalytic functions - example being haemoglobin

Question 24

What are precursor enzymes ?

Answer 24

• Enzymes that are produced in an inative form - particularly enzymes whose actions can cause damage within the cells

Question 25

How are precursor enzymes activated ?

Answer 25

• Undergo a change in their active site tertiary structure done through adding a cofactor