9.3 Glycolysis Flashcards
When is glycolysis the primary pathway for ATP synthesis?
in anaerobic conditions and in cells lacking a mitochondria
How many steps, enzymes, and intermediates are there?
10 steps, 10 enzymes, 9 intermediates
Where does glycolysis take place?
cytosol
What does glycolysis use?
1 glucose, 2 NAD+, 2 ADP, 2 Pi
What does glycolysis generate?
2 pyruvates 2 NADH, 2 H+, 2 ATP, 2 H2O
What is the net reaction?
Glucose + 2 NAD+ + 2 ADP + 2Pi <–> 2 Pyruvate + 2 NADH + 2 H+ + 2ATP + 2 H2O
Why so many steps?
Too much energy with one step, too much energy wasted, efficient energy usage through smaller steps
Why 10 steps for 2 ATP?
Pyruvate production is important for later energy generation, NADH electron carrier, 32 ATP made from 1 glucose
Kinase
Transfers a phosphate group between ATP and another substrate. Used to make or consume ATP.
Isomerase
Changes structure of substrate; molecular formula remains the same, creates isomers, reversible
Phosphatase
Removes phosphate group from a substrate, ATP not involved, release Pi
Other Enzymes involved:
adolase, mutase, enolase
What are the major events of stage 1?
2 ATP consumed, creates negatively charged molecules that can’t diffuse out of cell, Produces 2 G3P for stage 2.
Which steps are most important in stage 1?
Steps 1 and 3
Reaction 1
Substrates: glucose, ATP
Products: glucose-6-phosphate, ADP
Enzyme: hexokinase or glucokinase (pancreas and liver)
IRREVERSIBLE
ATP consumption
Phosphorylation prevents glucose from leaving cell
What inhibits hexokinase?
Glucose 6-P inhibits hexokinase. Feedback inhibition - products inhibit; Glucose-6-P binds to hexokinase and inhibits ATP binding by allosteric regulation
Reaction 2
Substrate: glucose-6-phosphate
Product: fructose-6-phosphate
Enzyme: phosphoglucose isomerase
Carbonyl moved from C1 to C2 (necessary for next step)
Concentration driven
Reaction 3
Substrates: fructose-6-phosphate, ATP
Products: fructose-1,6-bisphosphate, ADP
Enzyme: phosphofructokinase-1 (PFK-1)
IRREVERSIBLE
ATP consumption
Allosterically regulated by energy charge
Rate-limiting step for the entire glycolysis pathway
Regulation of PFK-1
Controlled by energy charge (ATP availability)
Activators: AMP, ADP, fructose-2,6-bisphosphate
Inhibitors: phosphoenolpyruvate, ATP
EC low - activate glycolysis
Active (R) state when ADP bound
Inactive (T) state when ATP bound
Reaction 4
Substrate: fructose-1,6-bisphosphate
Products: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
Enzyme: aldolase
Reverse aldol concentration; create ketone and aldehyde
Cellular metabolite concentrations favor forward reactions
Reaction 5
Substrate: dihydroxyacetone-P
Product: glyceraldehyde-3-P
Enzyme: triose phosphate isomerase
Enediol intermediate
Both products from reaction 4 -> single pathway
What are the major events in stage 2?
2 Glyceraldehyde-3-P enter, 4 ATP produced (net gain 2), 2 NADH produced, 2 H+ produced
Reaction 6
2x substrates: G-3-P, NAD+, Pi
2x products: 1,3-bisphosphoglycerate, NADH, H+
Enzyme: glyceraldehyde-3-phosphate dehydrogenase
NADH production
Oxidation of C1
Product quickly consumed, coupled with step 7
Reaction 7
2x Substrates: 1,3-bisphosphoglycerate, ADP
2x Products: 3-phosphoglycerate, ATP
Enzyme: phosphoglycerate kinase
ATP production (2)
Intermediate 2,3-BPG
Coupled with step 6
Reaction 8
2x Substrate: 3-phosphoglycerate
2x Product: 2-phosphoglycerate
Enzyme: phosphoglycerate mutase
Shift phosphate C3 to C2
Reaction 9
2x Substrate: 2-phosphoglycerate
2x Product: phosphoenolpyruvate (PEP), H2O
Dehydration reaction
Reaction 10
2x Substrate: PEP, ADP
2x Product: pyruvate, ATP
Enzyme: pyruvate kinase
IRREVERSIBLE
2 ATP
Actually 2 coupled reaction
Which steps are irreversible?
1,3,10 are irreversible steps - highly exergonic
Energy molecules produced?
Net gain 2 ATP, 2 NADH
What is NADH used for?
To make ATP in oxidative phosphorylation
