Topic 8

Question 1

The enzyme ATP synthase has an essential role in aerobic cell respiration.

The sketch shows the relationship between the reaction rate and substrate concentration in the presence and the absence of a competitive inhibitor.

Explain the effect of the competitive inhibitor on the reaction rate.

[2]a.
Describe its location.

[1]b.i.
Describe its function.

[2]b.ii.

Answer 1

a. competitive inhibitor «slows the reaction rate as it» competes for the active site
OR
competitor has similar shape/structure/composition to substrate «and slows the reaction rate»

b. binding of competitor is reversible
c. «as the substrate concentration increases» more substrate binds to the active site than the competitor «and reaction rate increases»
d. «as the substrate concentration increases» the reaction rate reaches the maximum plateau «same as with no inhibitor»

a.
the inner mitochondrial membrane critstae/thylakoid membrane

b.i.

Question 2

Outline the importance of enzymes to metabolic processes.

Answer 2

increase rate of reaction/speed up reaction

b. lower activation energy
c. a specific enzyme for each reaction/substrate
d. metabolic process/pathway blocked if an enzyme is inhibited/absent
e. end-product inhibition can control metabolic pathways
f. differences in metabolism as cells produce different enzymes during differentiation

b.

Question 3

Compare competitive and non-competitive enzyme inhibition

Answer 3

Competitive = bind to the active site, slows down the rate of reaction, shape is similar to the substrate, prevents binding of substrate to enzyme.

Non competitive = Binds to an allosteric site, slows down the rate of reaction, inhibitor is shaped different to substrate, changes active site of enzyme

Question 4

The activity of hexokinase is regulated by end product inhibition. Explain how a reaction can be controlled by end product inhibition.

Answer 4

. metabolic pathway is a series of enzyme catalysed reactions;

b. allosteric enzyme catalyses one step/first step in the mechanism/chain of reactions;
c. enzyme is inhibited by the end product;
d. end product binds at a site other than the active site/allosteric site;
e. reaction mechanism is interrupted / product formation stops;
f. more inhibition of enzyme as end product concentration rises / less inhibition as end product reduces;
g. example of negative feedback;

Question 5

What do metabolic pathways consist of?

Answer 5

Chains and cycles of enzyme catalysed reactions

Question 6

What are the common patterns of metabolic pathways?

Answer 6

• Happen in a sequence of small steps
• Chain of reaction
• In some form of cycle where the end product of one reaction is the reactant that starts the rest of the pathway

Question 7

What happens when an enzyme catalyses a reaction?

Answer 7

Substrate binds to the active site and the shape is altered to reach the transition state. The substrates are then converted into products. The binding of the substrate and enzyme lowers the Ea of the transition state and the Ea of the reaction

Question 8

What can enzyme inhibitors be?

Answer 8

Competitive or non competitive

Question 9

What are inhibitors?

Answer 9

Substances that bind to enzymes in order to reduce enzyme activity

Question 10

Draw a graph showing the effect on enzyme inhibitors ( competitive and non competitive)

Question 11

What can metabolic pathways be controlled by?

Answer 11

End product inhibition

Question 12

Describe end product inhibition

Answer 12

The enzyme that is regulated catalyses one of the first reactions in a metabolic pathway and the substance that binds to the allosteric site is the end product

Question 13

End product inhibition reaction do not often go to….

Answer 13

Completion ( equilibrium position reached instead)

Question 14

What does phosphorylation?

Answer 14

Making molecules less stable

Question 15

Describe the process of glycolysis

Answer 15

• Hexose sugar is phosphorylated by 2 ATP molecules to get hexose biophosphate
• hexose biophosphate is split into two triose phosphates
• H atoms removed by oxidation to reduced NAD+ and NADH+ + H+
• 4 molecules of ATP produced but only two are used
• two used are pyruvate ( 3C)

Question 16

Where does glycolysis take place?

Answer 16

Cytosol ( cytoplasm)

Question 17

Anaerobic vs aerobic respiration

Answer 17

Anaerobic : no further oxidation ( pyruvate remains in the cytosol and is converted into lactic acid in animals and CO2 in plants

Aerobic : pyruvate moves to the mitochondria for further brerakdown. Involves the link reaction, Krebs then electron transport chain

Question 18

What are the summarised 3 steps of the electron transport chain?

Answer 18

• proton pumps create an electrochemical gradient
• ATP synthase uses the diffusion of protons to synthesis ATP
• O2 accepts electrons and protons to form water

Question 19

Describe the process of the electron transport chain

Answer 19

1. a proton motion gradient is created by the hydrgen carriers are oxidised and release electrons which are transferred through the electron transport chain and loose energy
2. H+ pumped from the matrix
3. the proton motion gradient causes the H+ ions to move down the conc gradient back to the matrix through ATP synthesase
4. H+ ions trigger the molecular rotation of the enzyme
5. O2 removes the de-energised electrons as it is the final electron acceptor and binds with the free protons

Question 20

Draw the structure of mitochondria

Question 21

What is anaerobic cell respiration?

Answer 21

Incomplete breakdown of organic compounds to produce smaller yield of ATP

Question 22

What is aerobic cell respiration?

Answer 22

The complete breakdown of organic compounds to produce a larger yield of ATP

Question 23

Describe the link reaction

Answer 23

• pyruvate is transported to the matrix from the cytosol by carrier proteins
• pyruvate is then decarboxylated ( loss of CO2)
• now has 2C then loses H atoms to form an acetyl group
• acetyl group combines with acetyl CoA
• occurs twice per molecule as there is 2 pyruvate molecules

Question 24

Lollipop Experiment

Answer 24

• Radioactive carbon-14 is added to a ‘lollipop’ apparatus containing green algae (Chlorella)
• Light is shone on the apparatus to induce photosynthesis
• After different periods of time, the algae is killed by running it into a solution of heated alcohol (stops cell metabolism)
• Dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds
• Any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X-ray film exposure)
• By comparing different periods of light exposure, the order by which carbon compounds are generated was determined
• Calvin used this information to propose a sequence of events known as the Calvin cycle (light independent reactions)