glycolysis

Question 1

Complete oxidation of glucose to CO2 and H2O

Answer 1

happens in 3 stages
1. glycolysis and pyruvate dehydrogenase
2. TCA cycle
3. electron transport chain

Question 2

transport of glucose into the cell

Answer 2

• glucose is highly polar, can’t enter by passive diffusion
• GLUTs residing in the cell membrane catalyze glucose import
• insulin stimulates GLUT-mediated glucose uptake in skeletal muscles and adipose tissue

Question 3

why are some tissues and cell types dependent on glycolysis for energy

Answer 3

• glycolysis happens under aerobic conditions (no oxygen needed)

Question 4

general overview of glycolysis

Answer 4

• happens in the cytosol
• contains 10 steps
• first 5 steps: preparatory phase (ATP is used to phosphorylate and activate glucose)
• next 5 steps: pay off phase (net generation of ATP)

Question 5

isoenzymes

Answer 5

two or more enzymes that catalyze the same reaction but are encoded in different genes

Question 6

Step 1 of glycolysis

Answer 6

• glucose becomes glucose-6-phosphate
• uses one ATP (first phosphorylation)
• enzyme: hexokinase

Question 7

Step 2 of glycolysis

Answer 7

• glucose-6-phosphate becomes fructose-6-phosphate
• enzyme: phosphohexose isomerase

Question 8

Step 3 of glycolysis

Answer 8

• fructose-6-phosphate becomes fructose 1,6-bisphosphate
• ATP is used (second phosphorylation)
• enzyme: phosphofructokinase

Question 9

Step 4 of glycolysis

Answer 9

• fructose 1,6-bisphosphate is split into two 3-carbon units
• enzyme: aldolase
• the 3-carbon units are dihydroxyacetone phosphate and glyceraldehyde 3-phosphate

Question 10

Step 5 of glycolysis

Answer 10

• DHAP is immediately isomerize to G3P
• enzyme: triose phosphate isomerase
• from this point onwards, 2 triode molecules are catabolized for each glucose we started with

Question 11

Step 6 of glycolysis

Answer 11

• G3P and Pi combine to form 1,3-bisphosphoglycerate
• the first high energy molecule is produced in glycolysis
• uses NAD+
• enzyme: G3P dehydrogenase

Question 12

Step 7 of glycolysis

Answer 12

• 1,3-bisphosphoglycerate becomes 3-phosphoglycerate
• produces and ATP
• enzyme: phosphoglycerate kinase
• the free energy of hydrolysis of the anhydride bond is recovered by ATP

Question 13

Step 8 of glycolysis

Answer 13

• 3-phosphoglycerate becomes 2-phosphoglycerate
• functional group moves positions on the molecule
• enzyme: phosphoglycerate mutase

Question 14

step 9 of glycolysis

Answer 14

• 2-phosphoglycerate becomes phosphoenolpyruvare
• water leaves (dehydration)
• enzyme: enolase

Question 15

step 10 of glycolysis

Answer 15

phosphoenol pyruvate becomes pyruvate
- the enrol form of pyruvate immediately becomes the keto form
- forms ATP
- enzyme: pyruvate kinase

Question 16

why is the free energy of hydrolysis much higher for the phosphate group on C-1 of 1,3-bisphosphogycerate than the one on C-3

Answer 16

• the phosphate group at C-1 forms an anhydride bond which has high energy
• the phosphate group at C-3 forms a phosphorylation-ester linkage which only releases a small amount of energy

Question 17

Why is Pi required for glycolysis to proceed

Answer 17

• it is an essential substrate in the rxn catalyzed by glyceraldehyde 3-phosphate dehydrogenase