Energy I

Question 1

what is catabolism?

Answer 1

It is the breakdown of complex molecules to release energy or carry out mechanical work.

Question 2

what is anabolism?

Answer 2

It is the synthesis of new molecules from less complex compounds.

Question 3

what is ATP in terms of energy/energy storage?

Answer 3

ATP is a body’s energy provision. It can act as both an acceptor and donator of energy. It acts as a short-term reservoir of energy.

Question 4

What regulates glycolysis?

Answer 4

Enzymes catalysing irreversible reactions are potential sites for regulation.
They are regulated by:
→reversible binding of allosteric effectors
→ covalent modification
→ transcription

Question 5

what is the total amount of energy available from the hydrolysis of ATP?

Answer 5

65kj/mole

Question 6

how much ATP do we use at rest?

Answer 6

40Kg/24hour

Question 7

how much ATP do we use during exercise?

Answer 7

0.5Kg/minute

Question 8

how much ATP does the body have? and how does it meet the demands of ATP needed?

Answer 8

100g
To meet the demands of the body it must re-synthesise ATP from ADP

this is largely done through oxidative phosphorylation and this takes place in the mitochondria

Question 9

what are the major oxidative pathways?

Answer 9

→Glycolysis

→Citric acid cycle

→Electron transport coupled to oxidative phosphorylation

→Fatty acid oxidation

Question 10

how is glucose converted to pyruvate?

Answer 10

→Glucose is phosphorylated by Hexokinase to G6P (using ATP, making ADP).

→ G6P is them converted to Fructose-6-phosphate.

→Fructose-6-phosphate is then phosphorylated by phospho-fructokinase (PFK) to Fructose 1,6 bisphosphate (using ATP, making ADP).

→ Fructose 1,6 bisphosphate is then converted to two C3 molecules,
Dihydroxy acetone phosphate and GAP (Glyceraldehyde-3-phosphate).

→These 2 molecules are kept in equilibrium, and it favours GAP.

→ GAP is then converted to phosphoenol pyruvate (using NAD+ and Pi, and ADP, making NADH and ATP).

→ Phosphoenol pyruvate is then converted by pyruvate kinase to pyruvate (using ADP, making ATP).

Question 11

List the three enzymes involved in glycolysis, and list what they are inhibited by.

Answer 11

→Hexokinase: - converts glucose to G6P - inhibited by G6P

→Phospho-fructokinase: - converts fructose-6-phosphate - inhibited by ATP, citrate and H+ (acids) - stimulated by F16BP and AMP (the inhibition of PFK leads to the inhibition of G6P)

→Pyruvate Kinase: - converts phosphoenol pyruvate to pyruvate - inhibited by ATP

Question 12

what enzymes does the liver have?

Answer 12

→ The liver has glucokinase which has a higher Km so it needs a higher concentration of glucose to be functional and is not inhibited by G6P unlike hexokinase.

→The liver is responsible for storing excess glucose, so when glucose levels are high glucokinase increases the rate of glycolysis.

Question 13

What difference in the cycle occurs when the respiration is anaerobic?

Answer 13

→Instead of pyruvate being converted to Acetyl CoA, in anaerobically respiring muscle, it is converted to lactate (using NADH, making NAD+).

→The lactate is then sent to the liver to be converted back into glucose (so that the build-up of acid doesn’t inhibit PFK), and put back into the cycle.

→The making of lactate uses NADH to make NAD+. This NAD+ is used in the conversion of GALP to phosphoenol pyruvate.

→continues until NAD+ is a limiting factor.

Question 14

how is glycolysis regulated in the muscles?

Answer 14

→ If there is a high concentration of ATP in the cell :

→(PFK) is inhibited by lowering its affinity to fructose-6-phosphate so pyruvate cannot be formed.

→PFK is also inhibited by low pH which means too much lactic acid is forming.

→High AMP or ADP levels activate PFK to synthesize more ATP. When muscles produce lactate it is exported and taken to the liver.

Question 15

how is glycolysis regulated in the liver?

Answer 15

→In the liver high levels of ATP inhibit PFK, it is also inhibited by citrate.

→ The liver has glucokinase which has a higher Km so it needs a higher concentration of glucose to be functional and is not inhibited by G6P unlike hexokinase.

→The liver is responsible for storing excess glucose, so when glucose levels are high glucokinase increases the rate of glycolysis.

Question 16

what is the difference between hexokinase and glucokinase?

Answer 16

→Hexokinase is found in all cells in the body
glucokinase is found in the liver and is not inhibited by G6P.
→Glucokinase has a higher Km.

Question 17

how are tumors and exercising muscles similar?

Answer 17

→both the tumor and the muscle generate ATP where there is very little oxygen.

Question 18

what are the differences between tumors and muscles?

Answer 18

→A rapidly growing tumor does not have sufficient blood supply to have enough oxygen so it respires anaerobically.

→Tumors are not susceptible to low pH like muscles are.

Question 19

how do tumors respond to low oxygen?

Answer 19

→A molecule that senses low oxygen is called HIF (hypoxia induced factor), the low oxygen stimulates the TF (stabilizes it) which express enzymes in the glycolytic pathway, it regulates glucose transporters (GLUT), hexokinase, PFK and aldolase are also used.

Question 20

Why ia glycolysis in the liver inhibited by citrate?

Answer 20

→The liver uses glucose and glycolysis as a source of carbon skeletons glycolysis in the liver is inhibited by citrate.
→High levels of citrate indicate the precursors of biosynthesis are abundant.

Question 21

How is glycolysis in the liver activated indirectly?

Answer 21

Indirect activation by F6P which is converted to Fructose 2,6 bisphosphate when blood glucose is high – example of feed forward regulation.