Energy Production From Carbohydrates

Question 1

What are the major functions of the pentose phosphate pathway?

Answer 1

Produce NADPH in cytoplasm, reducing power for anabolic processes, maintains free -SH in RBC on cysteine, produce C5 ribose

Question 2

Write a reaction for phase I of pentose phosphate pathway

Answer 2

G6P + 2NADP —> C5 sugar phosphate + 2NADPH + 2H+ + 2CO2

Question 3

Write a reaction for phase II of pentose phosphate pathway

Answer 3

3C5 sugar phosphate —> 2 fructose-6-phosphate + glyceraldehyde-3-phosphate

Question 4

What happens in G6PDH deficiency?

Answer 4

Disulphide bridge formation in RBC due to low levels of NADPH. Insoluble aggregates called heinz bodies form - premature destruction of RBC

Question 5

Draw out the glycolysis pathway

Answer 5

Question 6

Give the equations for the 3 committing steps in glycolysis

Answer 6

Glucose —> G6P

F6P —> F-1,6-P

PEP —> pyruvate

Question 7

What does pyruvate dehydrogenase catalyse?

Answer 7

This reaction is irrversible

Question 8

What control mechanisms is PDH subject?

Answer 8

Acetyl CoA allosterically inhibits PDH, ADP promotes, ATP/NADH inhibit, activated when there is a lot of glucose

Question 9

What are the functions of glycolysis?

Answer 9

Oxidises glucose, 2 NADH produced, net synthesis of 2 ATP, produces C6 and C3 intermediates (glycerol phosphate, 2,3-BPG)

Question 10

What ismoers are carbohydrates usually found in the body?

Answer 10

D isomers

Question 11

List the main features of glycolysis

Answer 11

Oxidative, exergonic, C6–>2 C3, no loss of CO2, ATP generated, useful intermediates, substrate level phosphorylation

Question 12

Write an equation for dihydroxyacetone phosphate going to glycerol phosphate

Answer 12

Question 13

What stimulates pyruvate kinase?

Answer 13

High insulin:glucagon ratio

Question 14

What inhibits phosphofructokinase?

Answer 14

High levels of ATP cause allosteric inhibition

Question 15

Where would you find glucokinase and hexokinase?

Answer 15

Hexokinase - liver and muscle

Glucokinase - liver only

Question 16

What stimulates hexokinase and glucokinase?

Answer 16

An increase in glucose (or a decrease in G6P)

Question 17

Why is lactate dehydrogenase needed?

Answer 17

RBC cannot regenerate NAD+ any other way

Question 18

Write the reaction that occurs in RBC to produce pyruvate

Answer 18

Question 19

Write the overall equation for glycolysis

Answer 19

Glucose + 2Pi + 2ADP + 2NAD+ —> 2 pyruvate + 2H2O + 2H+ + 2NADH + 2ATP

Question 20

Draw out the TCA cycle

Answer 20

Question 21

Where does the TCA cycle occur?

Answer 21

Mitochondiral matrix

Question 22

What does the TCA pathway require?

Answer 22

NAD+, FAD and oxaloacetate

Question 23

What is the main function of the TCA cycle?

Answer 23

Break the C-C bond in acetate and oxidise the atoms to CO2. Doesn’t function anaerobically

Question 24

Approximately how many molecules of ATP are produced per molecule of glucose in the TCA cycle?

Answer 24

36 molecules of ATP per molecule of glucose

Question 25

What are the catabolic functions of the TCA cycle?

Answer 25

Produces intermediates and interconvertible acids

Question 26

What are the anabolic functions of the TCA cycle?

Answer 26

Synthesis of non-essential amino acids, synthesis of haem and glucose, synthesis of fatty acids

Question 27

What are the two major signals for the TCA cycle?

Answer 27

ATP/ADP ratio and NADH/NAD+ ratio

Question 28

What is removed from acetate and which molecules accept them?

Answer 28

H+ and e- are removed by NAD+ and FAD

Question 29

Where does oxidative phosphorylation occur?

Answer 29

Inner mitochondrial membrane

Question 30

Briefly describe oxidative phosphorylation

Answer 30

e-‘s from NADH and FADH2 are transferred to O2, releasing energy. This can be used to drive ATP synthesis

Question 31

What is the role of proton translocating complexes?

Answer 31

Move protons from inside the inner mitochondrial matrix to outside the inner mitochondrial matrix, causing an increase in H+ and therefore creating proton motive force. 3 out of 4 complexes are PTC

Question 32

Describe the effect of the proton motive force

Answer 32

As the inner mitochondrial membrane is impermeable to protons there is a build up of H+. Protons can only re-enter the mitochondrial matrix via ATPsynthase complexes.

Question 33

How many moles of ATP can 2 moles of NADH produce?

Answer 33

5 moles of ATP

Question 34

How many moles of ATP can 2 moles of FADH2 produce?

Answer 34

3 moles of ATP

Question 35

Describe what happens in the mitochondria when ATP is high

Answer 35

ATPsynthase stops (lack of substrate), prevents H+ moving back into the mitochondria, H+ conc out increases such that protons cannot be pumped out, electron transport stops

Question 36

What is the function of uncoupling proteins?

Answer 36

Uncouple electron transport from ATP production to produce heat (leaky membranes)

Question 37

What does UCP1 do?

Answer 37

Expressed in brown adipose and is involved in non-shivering thermogenesis

Question 38

What does UCP2 do?

Answer 38

Linked to obesity, metabolic syndrome and heart faiulre

Question 39

What does UCP3 do?

Answer 39

Found in skeletal muscle, brown adipose and heart. Involved in modifying fatty acid metabolism and in protecting against ROS damage

Question 40

What does noradrenaline stimulate?

Answer 40

Lipolysis - fatty acids - NADH/FAD2H - increase in pmf

Also activates UCP1

Question 41

Describe the differences between substrate level phosphorylation and oxidative phosphorylation

Answer 41