M2 CH4: Enzymes

Question 1

give 2 examples of extracellular enzymes, and what they do.

Answer 1

Amylase: catalyses the hydrolysis of starch into maltose.

trypsin: catalyses the hydrolysis of peptide bonds (breakdown of polypeptides)

Question 2

give an example of an intracellular enzyme and what it does.

Answer 2

catalase: catalyses breakdown of hydrogen peroxide into oxygen and water

Question 3

outline general information about the structure of enzymes.
(3)

Answer 3

globular protein
tertiary structure
active site with specific shape

Question 4

explain how enzymes work.

Answer 4

lowers the activation energy (minimum amount of energy needed to start the reaction)

Question 5

outline how the induced fit hypothesis differs from the lock and key model

Answer 5

induced fit: explains that as the substrate binds, the active site changes shape slightly to fit the substrate more closely

Question 6

give the equation for the temperature coefficient

Answer 6

rate at higher temperature/ rate at lower temperature

Question 7

outline how to conduct an investigation into the effect of temperature on enzyme activity

Answer 7

enzyme: catalase
1. boiling tubes containing same conc and volume of hydrogen peroxide. add equal volumes of buffers to each tube
2. set up an upside down measuring cylinder into a cup of water, with a hydrogen peroxide solution tube with a bung and delivery tube feeding from the bung into under the upside down cylinder
3. put each boiling tube in a water bath set to different temperatures as well as tube of catalase.
4. add equal volumes of catalase using a pipette to each boiling tube
5. record how much oxygen is produced in the first 60s of reaction.
6. repeat the experiment at each temperature 3x
7. calculate the mean rate of reactions

Question 8

outline how competitive inhibition works, and the effect of increasing substrate concentration

Answer 8

inhibitor binds to AS, preventing substrate from binding
subs concentration increases likelihood of subs getting to active site before inhibitor does

Question 9

outline how non competitive inhibition works, and the effect of increasing substrate concentration

Answer 9

molecule binds to allosteric site, changing the tertiary structure of the AS so the substrate can no longer fit
increasing the concentration of subs has no impact- substrate can no longer fit

Question 10

explain how end product inhibition works

Answer 10

the final product in metabolic pathway inhibits enzyme that acts earlier in pathway
it is reversible

Question 11

give an example of end product inhibition

Answer 11

ATP and phosphofructokinase
a high level of ATP inhibits phosphofructokinase production, and so no more atp is made

Question 12

distinguish cofactors and coenzymes

Answer 12

cofactors:
inorganic molecules
not used up or changed in reactions
help enzyme and subs bind

coenzymes:
organic molecules
changed in reactions
move chemical groups between different enzymes