Energy Production From Carbohydrates Flashcards
What are the major functions of the pentose phosphate pathway?
Produce NADPH in cytoplasm, reducing power for anabolic processes, maintains free -SH in RBC on cysteine, produce C5 ribose
Write a reaction for phase I of pentose phosphate pathway
G6P + 2NADP —> C5 sugar phosphate + 2NADPH + 2H+ + 2CO2
Write a reaction for phase II of pentose phosphate pathway
3C5 sugar phosphate —> 2 fructose-6-phosphate + glyceraldehyde-3-phosphate
What happens in G6PDH deficiency?
Disulphide bridge formation in RBC due to low levels of NADPH. Insoluble aggregates called heinz bodies form - premature destruction of RBC
Draw out the glycolysis pathway
Give the equations for the 3 committing steps in glycolysis
Glucose —> G6P
F6P —> F-1,6-P
PEP —> pyruvate
What does pyruvate dehydrogenase catalyse?
This reaction is irrversible
What control mechanisms is PDH subject?
Acetyl CoA allosterically inhibits PDH, ADP promotes, ATP/NADH inhibit, activated when there is a lot of glucose
What are the functions of glycolysis?
Oxidises glucose, 2 NADH produced, net synthesis of 2 ATP, produces C6 and C3 intermediates (glycerol phosphate, 2,3-BPG)
What ismoers are carbohydrates usually found in the body?
D isomers
List the main features of glycolysis
Oxidative, exergonic, C6–>2 C3, no loss of CO2, ATP generated, useful intermediates, substrate level phosphorylation
Write an equation for dihydroxyacetone phosphate going to glycerol phosphate
What stimulates pyruvate kinase?
High insulin:glucagon ratio
What inhibits phosphofructokinase?
High levels of ATP cause allosteric inhibition
Where would you find glucokinase and hexokinase?
Hexokinase - liver and muscle
Glucokinase - liver only
What stimulates hexokinase and glucokinase?
An increase in glucose (or a decrease in G6P)
Why is lactate dehydrogenase needed?
RBC cannot regenerate NAD+ any other way
Write the reaction that occurs in RBC to produce pyruvate
Write the overall equation for glycolysis
Glucose + 2Pi + 2ADP + 2NAD+ —> 2 pyruvate + 2H2O + 2H+ + 2NADH + 2ATP
Draw out the TCA cycle
Where does the TCA cycle occur?
Mitochondiral matrix
What does the TCA pathway require?
NAD+, FAD and oxaloacetate
What is the main function of the TCA cycle?
Break the C-C bond in acetate and oxidise the atoms to CO2. Doesn’t function anaerobically
Approximately how many molecules of ATP are produced per molecule of glucose in the TCA cycle?
36 molecules of ATP per molecule of glucose
What are the catabolic functions of the TCA cycle?
Produces intermediates and interconvertible acids
What are the anabolic functions of the TCA cycle?
Synthesis of non-essential amino acids, synthesis of haem and glucose, synthesis of fatty acids
What are the two major signals for the TCA cycle?
ATP/ADP ratio and NADH/NAD+ ratio
What is removed from acetate and which molecules accept them?
H+ and e- are removed by NAD+ and FAD
Where does oxidative phosphorylation occur?
Inner mitochondrial membrane
Briefly describe oxidative phosphorylation
e-‘s from NADH and FADH2 are transferred to O2, releasing energy. This can be used to drive ATP synthesis
What is the role of proton translocating complexes?
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
Describe the effect of the proton motive force
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.
How many moles of ATP can 2 moles of NADH produce?
5 moles of ATP
How many moles of ATP can 2 moles of FADH2 produce?
3 moles of ATP
Describe what happens in the mitochondria when ATP is high
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
What is the function of uncoupling proteins?
Uncouple electron transport from ATP production to produce heat (leaky membranes)
What does UCP1 do?
Expressed in brown adipose and is involved in non-shivering thermogenesis
What does UCP2 do?
Linked to obesity, metabolic syndrome and heart faiulre
What does UCP3 do?
Found in skeletal muscle, brown adipose and heart. Involved in modifying fatty acid metabolism and in protecting against ROS damage
What does noradrenaline stimulate?
Lipolysis - fatty acids - NADH/FAD2H - increase in pmf
Also activates UCP1
Describe the differences between substrate level phosphorylation and oxidative phosphorylation
