steps of glycolysis

Question 1

Step 1 (mechanism)

Answer 1

Phosphorylation of glucose. 
enzyme: hexokinase
reactants: glucose and ATP
products: glucose-6-phosphate and ADP
∆G= spontaneous, irreversible
Nucleophilic oxygen at C6 of glucose attacks gamma phosphate of ATP, facilitated by ATP-bound Mg2+ shielding 
slide 13

Question 2

Step 1 (info)

Answer 2

Phosphorylation of glucose
rationale: traps glucose inside the cell. lowers intracellular glucose concentration to allow further uptake
ATP is CONSUMED
hexokinase in eukaryotes, glucokinase in prokaryotes

Question 3

Step 2 (mech)

Answer 3

Phosphohexose Isomerization
enzyme: phosphohexose isomerase
reactants: glucose-6-phosphate
products: fructose-6-phosphate
∆G: non-spontaneous, reversible (P conc kept low to drive forward)
Goes through enediol intermediate, catalyzed by active site glutamate
slide 16

Question 4

Step 2 (info)

Answer 4

Phosphohexose Isomerization
rationale: C1 of fructose is easier to phosphorylate by PFK and fructose allows for symmetrical cleave by aldolase
Goes through enediol intermediate, catalyzed by active site glutamate

Question 5

Step 3 (mech)

Answer 5

2nd Priming phosphorylation
enzyme: phosphofructokinase-1 (PFK-1)
reactants: fructose-6-phosphate and ATP
products: fructose-1,6-biphosphate and ADP
∆G: spontaneous, irreversible 
slide 17 (didn't draw mech...)

Question 6

Step 3 (info)

Answer 6

2nd Priming phosphorylation
rationale: further activation of glucose allows for 1 phosphate per 3-carbon sugar after step 4, more bang for buck
this is the first Committed step of glycolysis, at this point we are fully committed to becoming pyruvate and energy. PFK-1 is highly regulated so that glucose is not burned unless necessary
ATP is CONSUMED

Question 7

Step 4 (mech)

Answer 7

Aldol cleavage of fructose-1,6-biphosphate
enzyme: aldolase
reactants: fructose-1,6-biphosphate
products: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate
∆G: non spontaneous, reversible (P conc kept low)
Lysine, gen acid, and gen base are important to know
slide 21

Question 8

Step 4 (info)

Answer 8

Aldol cleavage of fructose-1,6-biphosphate
rationale: cleavage of a 6C sugar into two 3C sugars, high energy phosphate 3C sugars is good bang for buck.
animal and plant aldolases employ covalent catalysis while fungal and bacterial aldolases employ metal ion catalysis

Question 9

Step 5 (mech)

Answer 9

Triose Phosphate Interconversion
enzyme: triose phosphate isomerase (perfect)
reactants: dihydroxyacetone phosphate
products: glyceraldehyde 3-phosphate
∆G: non spontaneous, reversible (P conc kept low)
slide 27

Question 10

Step 5 (info)

Answer 10

Triose Phosphate Interconversion
rationale: allows glycolysis to proceed by one pathway (just glyceraldehyde 3-phosphate is substrate for next enzyme)
completes preparatory phase

Question 11

Step 6 (mech)

Answer 11

Oxidation of GAP
enzyme: glyceraldehyde 3-phosphate dehydrogenase
reactants: (2) glyceraldehyde 3-phosphate, Pi, and NAD
products: (2) 1,3-Bisphosphoglycerate and NADH
∆G: non spontaneous, reversible (coupled to next reaction)
active site cysteine forms high energy thioester intermediate
slide 31

Question 12

Step 6 (info)

Answer 12

Oxidation of GAP
rationale: generation of a high energy phosphate compound and incorporates inorganic phosphate, which allows for net production of ATP
First energy yielding step, NADH is PRODUCED

Question 13

Step 7 (mech)

Answer 13

1st Production of ATP
enzyme: phosphoglycerate kinase
reactants: (2) 1,3-biphosphoglycerate and ADP
products: (2) 3-phosphoglycerate and ATP
∆G: spontaneous, irreversible
slide 32 (no mech shown...)

Question 14

Step 7 (info)

Answer 14

1st Production of ATP

rationale: substrate level phosphorylation to make ATP

Question 15

Step 8 (mech)

Answer 15

Migration of the Phosphate
enzyme: phosphoglycerate mutase
reactants: (2) 3-phosphoglycerate
products: (2) 2-phosphoglycerate
∆G: non spontaneous, reversible (R conc kept high)
one enzyme histidine is modified to phosphohistidine
slide 36

Question 16

Step 8 (info)

Answer 16

Migration of the phosphate
rationale: be able to form high energy phosphate compound
uses mutase which only apparently migrates phosphate, remember the phosphate group is actually taken by a histidine and then a phosphohistidine donates its phosphate group to a new position.

Question 17

Step 9 (mech)

Answer 17

Dehydration of 2-Phosphoglycerate to PEP
enzyme: enolase
reactants: (2) 2-phosphoglycerate
products: (2) Phosphoenolpyruvate (PEP) and H2O
∆G: non spontaneous, reversible (P conc kept low)
slide 37

Question 18

Step 9 (info)

Answer 18

Dehydration of 2-PG to PEP
rationale: generate a high energy phosphate compound, the PEP is needed for ADP –> ATP as 2-PG is not a good enough phosphate donor

Question 19

Step 10 (mech)

Answer 19

2nd Production of ATP
enzyme: pyruvate kinase
reactants: (2) phosphoenolpyruvate (PEP) and ADP
products: (2) pyruvate and ATP
∆G: spontaneous, irreversible
slide 39

Question 20

Step 10 (info)

Answer 20

2nd Production of ATP
rationale: substrate level phosphorylation to make ATP, this step creates a net production of 2 ATP per glucose
recall that PEP hydrolysis is very favorable due to tautomerization