ENZYMES (2.1.4)

Question 1

state the function of an enzyme

Answer 1

• speed up chemical reactions without being used up itself
• catalyze reactions at cellular levels and for the whole organism (e.g.respiration vs digestion)
• affect an organisms structure (catalyse reactions that produce structural components e.g. collagen, cellulose)

Question 2

what is an intracellular enzyme with an example(s)

Answer 2

• enzymes that work within cells (present within plasma membrane)
• Ex. Catalase

Question 3

• where is catalase found?
• what is catalase’s function?

Answer 3

• animal + plant tissues (e.g. liver cells)
• catalyses breakdown of hydrogen peroxide into H2O and O2
• 2H2O2 is a toxic by-product of cellular reactions

Question 4

what is an extra cellular enzyme with an example(s)

Answer 4

• enzymes that work outside cells,
• present in tissue spaces, bodily fluids, cavities of organs (e.g. stomach)
  Ex. Amylase, Trypsin, Maltase

Question 5

• where is amylase found?
• what is its function?

Answer 5

• small intestine, salivary gland, pancreas
• catalyses hydrolysis of:
  starch ➡️ maltose (disaccharide)

Question 6

• where is trypsin found?
• what is its function?

Answer 6

• pancreas (secreted into small intestine)
• catalyses hydrolysis of peptide bonds:
  big polypeptides ➡️ small polypeptides

Question 7

• where is maltase found?
• what is its function?

Answer 7

• small intestine
• catalyses hydrolysis of
  maltose ➡️ 2 glucose molecules

Question 8

explain how the type of protein that enzymes are affects their function

Answer 8

• globular proteins
• tertiary structure determines shape of active site, determining which complementary substrate binds to it and ultimately decides the enzymes function

Question 9

describe the lock and key model of enzyme action

Answer 9

• early model
• enzyme and substrate have complementary shapes
• fit together perfectly to form enzyme-substrate complex
• enzymes active site remains unchanged

Question 10

describe the induced fit model of enzyme action

Answer 10

• modified model
• enzymes active site changes shape slightly to accommodate for the substrate
• explains why enzymes are so specific in their bonding to particular substances

Question 11

explain how enzymes speed up the rate of reactions

Answer 11

• lowers the activation energy
• allows reactions to happen at lower temperatures

Question 12

define activation energy

Answer 12

the energy required to be supplied to chemicals for a reaction to start
(often in the form of heat)

Question 13

explain how temperature affects enzyme activity

Answer 13

1. • increased heat means increased KE of molecules
     - substrate molecules are more likely to have successful collisions with the enzyme
2. • enzyme molecules vibrate, breaking H bonds in the tertiary structure
     - causes enzyme’s active site to change, becoming denatured
     - no longer fits substrate, can’t catalyses reactions

Question 14

• define temperature co-efficient
• state the equation

Answer 14

• how much R.O.R changes when temperature is increased by 10
• Q10 = R2/R1
  (R2= rate at high temp)
  (R1= rate at low temp)

Question 15

explain how pH affects enzyme activity

Answer 15

• too high or low pH values stop enzyme activity
• H+ and OH- ions in acids and alkalis can break hydrogen and ionic bonds in the tertiary structure
• this causes the active site to change shape, denaturing the enzyme

Question 16

explain how enzyme concentration affects enzyme activity

Answer 16

1. • increasing causes a steady increase in R.O.R, as there are more active sites available
     - therefore more likely for S molecules to have successful collisions, forming E-S complex
2. • if amount of substrate is limited, adding more enzymes has no effect
     - this is because there is more than enough enzyme molecules

Question 17

explain how substrate concentration affects enzyme activity

Answer 17

1. • increasing causes a steady increase in R.O.R, as it it more likely for successful collisions to occur and form E-S complexes
2. • once all active sites become full, adding more S molecules has no effect

Question 18

what is a cofactor/coenzyme

Answer 18

non-protein substances that bind to enzymes, helping their functions

Question 19

• what is an inorganic cofactor?
• outline their purpose

Answer 19

• molecules and ions
• help enzyme and substrate bind together

Question 20

• explain how inorganic cofactors work
• give an example of an inorganic cofactor

Answer 20

• bind temporarily to the enzyme and aren’t changed, used up or involved in the reaction
• Cl- ions are cofactors with the enzyme amylase (starch ➡️ maltose)

Question 21

• what is a coenzyme
• outline their purpose

Answer 21

• an organic cofactor
• help by moving chemical groups between different enzymes

Question 22

• explain how coenzymes work
• give an example of a coenzyme

Answer 22

• temporarily binds to an enzyme and is involved in the reaction, so is changed in some way
• this allows it to be recycled/ used by another enzyme
• vitamins e.g NAD derived from vitamin B3

Question 23

• what is a prosthetic group
• outline their purpose

Answer 23

• non protein groups
• help the normal functioning of an enzyme by adding to its 3D shape

Question 24

• explain how prosthetic groups work
• give an example of a prosthetic group

Answer 24

• permanently bind to an enzymes active site, so changes the active site’s shape
• Zinc 2+ ions are a prosthetic group for carbonic anhydrase
  (catalyses carbon dioxide + water ➡️ carbonic acid)

Question 25

explain how competitive inhibitors work

Answer 25

- similar shape to substrate, so competes with it - blocks the active site from substrate

Question 26

explain how increasing substrate conc affects R.O.R with competitive inhibitors present

Answer 26

- increasing substrate means they will out-compete the inhibitors - allows increased R.O.R

Question 27

explain how non-competitive inhibitors work

Answer 27

- bind to the enzymes allosteric site - this changes the shape of the active site - this means the active site will no longer be complementary to the substrate

Question 28

explain how increasing substrate conc affects R.O.R with non-competitive inhibitors present

Answer 28

- increasing substrate conc will make no change, as NCI’s do not compete with them - the active sites will be changed, so will no longer allow substrates to fit

Question 29

explain why some inhibition is irreversible

Answer 29

the enzyme and inhibitor have strong covalent bonds between each other

Question 30

explain why some inhibition is reversible

Answer 30

due to weak hydrogen or ionic bonds between the enzyme and the inhibitor

Question 31

explain how antiviral drugs act as inhibitors

Answer 31

REVERSE TRANSCRIPTASE INHIBITOR - stops the enzyme RT from catalyzing virus replication

Question 32

explain how antibiotics act as inhibitors

Answer 32

PENICILLIN - inhibits enzyme from catalysing formation of bacterial cell walls

Question 33

explain how cyanide acts as a non-competitive inhibitor

Answer 33

- binds to allosteric site of cytochrome C oxidase - results in no respiration - cells die

Question 34

- explain what is meant by end-product inhibition - explain why it is necessary

Answer 34

- when the final product in a metabolic pathway inhibits an enzyme from earlier on - controls how much product is made, reversible process

Question 35

explain why some enzymes are synthesized as inactive precursors

Answer 35

- example of inhibition being used for protection - prevents the enzyme from becoming active until it is where it needs to be - then the inhibiting part it removed