Biochem: sugar metabolic pathways

Question 1

What are the advantages of phosphorylation in the glycolysis?

Answer 1

1. there are no transporters for phosphorylated sugars (ensures that the sugar remains in the cell for the whole process)
2. phosphoric group generates energy
3. phosphoric groups lower the required activation energy

Question 2

steps of the glycolysis

Answer 2

1. glucose phosphorylation (glucose –> G6P) by hexokinase: using ATP molecule that is attached to Mg2+ ion (MgATP).
2. G6P to Fructose 6 P (F6P) by phosphohexose isomerase (also using a Mg2+ ion)
3. F6P to fruit 1,6 bisphosphate by the enzyme PFK1: also using MgATP; it is the faith determining step of the glycolysis as no other process is using F1,6BP.
4. breaking down F1,6BP to DHAP and glyceraldehyde-3-phosphate by the enzyme aldolase (both products are trioses)
5. DHAP and glyceraldehyde-3-phosphate are converted to one another by the enzyme triode phosphate isomerise

*** beginning of payoff time

6. glyceraldehyde-3-phosphate to 1,3 bisphosphoglycerate by the enzyme glyceraldehide-3-phosphate DH; using NAD+ as co factor and we get NADH
7. 1,3 bisphosphoglycerate to 3 phosphoglycerate by the enzyme phosphoglycerate kinase –> we get 1 ATP molecule from the reaction
8. 3 phosphoglycerate to 2 phosphoglycerate by the enzyme phosphoglycerate mutase
9. 2 phosphoglycerate to phosphoenolpyruvate by the enzyme enolase
10. phosphoenolpyruvate to pyruvate by phosphorylating ADP to ATP by the enzyme pyruvate kinase

Question 3

What are the 3 fates of pyruvate?

Answer 3

pyruvate can be a part of 3 different metabolic pathways and become 3 different molecules:

1. lactate (lactic fermentation)
2. ethanol (alcoholic fermentation)
3. Acetyl CoA (Krebs cycle)

Question 4

how is glucose and glycolysis related to cancer diagnosis and treatment?

Answer 4

Due to their high growth and division rate, cancer cells rely heavily on anaerobic respiratory and therefore show increased rates of glycolysis. the high glucose consumption by cancer cells have therefore become a reliable way to diagnose cancer using PET-scans that show the areas that use up the highest amount of glucose (using a contrast agent). The effect is called Werburg effect.

Question 5

Why do cells do fermentation under anaerobic conditions

Answer 5

NAD+ is important for stage 6 of the glycolysis (G3P to 1,3 bisphosphoglycerate). if a cell has to relay on glycolysis to produce ATP in anaerobic conditions, the cell runs out of NAD+ (as it has a lot of NADH which is not used for the electron transport chain).

Therefore when the cell cannot move onto the electron transport chain, the cell re-oxidises NADH to NAD+ by fermentation whereby pyruvate donates electrons and reduced to lactate

Question 6

What is the cori cycle?

Answer 6

the process of converting glucose to lactate in muscles during acute physical exercise and converting lactate to glucose by gluconeogenesis in the liver to replenish glucose storages that were used by the muscles.

Question 7

What is Thyamin pro phosphate (TPP) and in which process is it involved?

Answer 7

TPP is a cofactor derived from vitamin b1, involved in alcoholic fermentation in bacteria and yeast. TPP is used by the enzyme pyruvate decarboxylase to generate acetaldehyde, and other processes where decarboxylation of carbonyl groups takes part (like in removing carbonyl from alpha-keno molecules by alpha-ketoglutarate DH, and in decarboxylation of pyruvate to acetyl CoA in the Krebs cycle);

deficiency in vitamin b1 results in diseases like Warenicke-Korsakoff syndrome and Beriberi

Question 8

what are the steps of gluconeogenesis (GNG)?

Answer 8

1. lactate/glycerol/AA converted to pyruvate
2. 2x pyruvate/lactate/alanin -> oxalacetate
3. oxalacetate -> PEP (a huge bypass process unique to GNG)
4. PEP -> 2-phosphogycerate
5. 2PG -> 3PG
6. 3PG -> 1,3 BPG
7. 1,3 BPG -> glyceraldehyde 3 phsphate
8. GA3P -> DHAP -> fructose 1,6 BP
9. fructose 1,6 BP -> fructose 6P
10. F6P -> G6P
11. G6P -> glucose

Question 9

How is Pyruvate converted to PEP and what is the difference between pyruvate and lactate availability?

Answer 9

using cytosolic enzymes a series of steps converts pyruvate to PEP:
1. pyruvate enters mitochondria -> ocxaloacetate by pyruvate carboxylase
2. oxaloacetate -> malate by malate DH and leave the mitochondria
3. malate -> oxaloacetate by malate DH
4. oxaloacetate -> PEP by PEP-carboxykinase

if lactate is available instead of pyruvate:
1. lactate -> pyruvate
2. pyruvate (moves into the mitochondria) -> oxaloacetate
3. oxaloacetate -> PEP

Question 10

What is the role of the enzyme Transketolase?

Answer 10

the enzyme is important fo the pentose phosphate pathway, (the unoxidised phase of the PPP). catalyses translocation of 2 C from ketone to aldose (at the stage where ribose-5-P is converted to glyceraldehyde-3-phospahte. Uses TPP for stabilising the 2 C whirly translocating it