Glucose Metabolism

Question 1

Why is glucose an excellent fuel?

Answer 1

• yields good amount of energy upon oxidation
• can be stored in polymers
• many organisms require it

Question 2

How is glucose a good biochemical precursor?

Answer 2

glucose can be used to generate:
- all AA’s
- membrane lipids
- nucleotides
- metabolic cofactors

Question 3

What are the 4 major pathways of glucose?

Answer 3

1. structural polymers (ECM, cell wall)
2. Storage (glycogen, starch, sucrose)
3. Oxidation via pentose phosphate (creates ribose 5-phosphate for nucleotide synthesis)
4. oxidation via glycolysis (pyruvate)

Question 4

What is the difference between a nonspontaneous and spontaneous reaction?

Answer 4

spontaneous: process that releases work (-ve ∆G)

nonspontaneous: requires work to be done (+ve ∆G)

Question 5

When was glycolysis discovered?

Answer 5

1897: fermentation discovered in cell free yeast extracts

1930: entirety of glycolytic pathway discovered

Question 6

What are the two phases of glycolysis and what does it produce? What is the net yield?

Answer 6

1. Energy Expenditure: glucose is split into 2 triose phosphates (costs 2 ATP)
2. Oxidation and phosphorylation (yield 1 NADH and 2 ATP per glucose)

Net yield: 2 ATP, 2 NADH

Question 7

What are the steps of glycolysis’s expenditure phase?

Answer 7

1. glucose is phosphorylated by hexokinase into glucose 6-phosphate (occurs on C6 as C1 is a carbonyl that cannot be phosphorylated)
2. glucose 6-phosphate is isomerized by phosphohexose isomerase into fructose 6 phosphate (isomerization moves carbonyl to C2 which is needed to set position for phosphorylation)
3. fructose 6 phosphate is phosphorylated by phosphofructokinase into fructose 1,6-bisphosphate (required to make DHAP and G3P inconvertible)
4. fructose 1,6 bisphosphate is split by aldolase into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3 phosphate (G3P)
5. Dihydroxyacetone phosphate (DHAP) is isomerized by triose phosphate isomerase into glyceraldehyde 3 phosphate (doubles pathway)

Question 8

What are the steps of glycolysis’s pay off phase?

Answer 8

1. Glyceraldehyde 3 phosphate is phosphorylated by glyceraldehyde-3-phosphate into 1,3 bisphosphoglycerate (need phosphate to make ATP)
2. 1,3 bisphosphoglycerate is dephosphorylated by phosphoglycerate kinase into 3 phosphoglycerate (to make ATP)
3. 3 phosphoglycerate is isomerized by 3 phosphoglycerate mutase into 2 phosphoglycerate (phosphoryl goup is moved to set up next step)
4. 2-phosphoglycerate is dehydrated by enolase into phosphoenol pyruvate (dehydration creates high energy compound for phosphoryl transfer)
5. Phosphoenol pyruvate is dephosphorylated by pyruvate kinase into pyruvate