Glycolysis Flashcards
Picture of the overview of glycolysis.
Second picture of overview of glycolysis.
Linear layout of glycolysis.
What are the characteristics of glycolysis?
The purpose of glycolysis is to break down glucose to pyruvate and 4 ATP + 2 NADH + 2 H+
It takes place in the cytosol of all cells
This is a catabolic rxn
What is the 1st reaction of glycolysis?
Glucose to Glucose-6-phosphate
Purpose: Trap glucose in the cell by adding the phosphate
Enzyme used: Transferase (Hexokinase)
Biochemical Process: Phosphorylation
Reaction is irreversible & spontaneous
This is a regulatory step which is negatively regulated by the presence of glucose-6-phosphate.
For each molecule of glucose, this rxn happens one time
What is the 2nd reaction of glycolysis?
Glucose-6-phosphate to fructose-6-phosphate
Purpose: reshuffle the phosphate group on glucose-6-phosphate
Enzyme category: Isomerase (Phosphohexose isomerase)
Biochemical process: Isomerization
This reaction is reversible & spontaneous
What is the 3rd reaction of glycolysis?
Fructose-6-phosphate to Fructose-1,6-bisphosphate
Purpose: Add energy to fructose-6-phosphate
Enzyme category: Transferase (Phospho-fructokinase [PFK])
Biochemical process: Phosphorylation
NOTE: This is the committed step of glycolysis because of its large -dleta G value.
Picture showing the control of the committed step (Fruuctose-6-phosphate to Fructose-1,6-bisphosphate) of glycolysis.
What is the 4th reaction of glycolysis?
Fructose-1,6-bisphosphate to glyceraldhyde-3-phosphate and dihydroxyacetone phosphate (DHAP)
Purpose: Split fructose-1,6-bisphosphate into two products
Enzyme: Lyase (Aldolase)
Biochemical process: Lysis
Reaction is reversible and non-spontaneous
Picture of 4th reaction of glycolysis.
What is the 5th reaction of glycolysis?
Dihydroxyacetone phosphate (DHAP) to glyceraldehyde-3-phosphate
Purpose: Reshuffle DHAP
Enzyme: Isomerase (Triose phosphate isomerase)
Biochemical process: Isomerization
Reaction is spontaneous and reversible
What are regulators of phosphofructokinase?
- ATP is an allosteric inhibitor of PFK. When ATP concentrations in the cell are high, the rate of glycolysis is reduced.
- AMP can reverse the inhibition produced by ATP. When ATP levels drop, ADP is converted to ATP and AMP through the action of adenylated kinase (thus, AMP concentration increases)
Thus, the energy status of the cell, as reflected in the relative concentrations of ATP and AMP, serves to regulate glycolysis by regulating the action of PFK
- Citrate is an allosteric inhibitor of PFK. Citrate is produced by the citric acid cycle Thus, if this “downstream” product accumulates, then the rate of glycolysis is reduced due to the inhibition of PFK.
What are the phases of glycolysis and what is the ultimate energy utilization & production of glycolysis?
- Phase I: In a series of five reactions where glucose is broken down into two molecules of glyceraldehyde-3-phosphate.
- Phase II: In a series of five more reactions the two molecules of glyceraldehyde-3-phosphate are converted into two molecules of pyruvate
- Phase I requires two molecules of ATP
- Phase II produces four molecules of ATP
- The net result is that glycolysis produces two molecules of ATP per molecule of glucose catabolized in this pathway
What is the fate of pyruvate produced by glycolysis?
- In aerobic organisms pyruvate is oxidized to CO2, and the acetyl group of an acetyl-coenzyme A molecule. This acetyl group is metabolized in the tricarboxylic acid cycle (TCA) to yield CO2. The electrons removed during this oxidation are passed through the mitochondrial electron transport system and generate ATP by oxidative phosphorylation.
- Under anaerobic conditions in contracting muscle pyruvate is reduced to lactate
- Under anaerobic conditions in yeast (“fermentation”) pyruvate is reduced to ethanol and CO2
What is the 6th reaction of glycolysis?
Glyceraldehyde-3-phosphate to 1,3-Bisphosphoglycerate.
Purpose: Add energy and generate a reducing equivalent
Enzyme; Oxidoreductase (Glyceraldehyde-3-phosphate dehydrogenase)
Biochemical process: Phosphorylation and dehydrogenation
Free energy change: -1.3 kj/mol
What is the 7th reaction of glycolysis?
1,3-Bisphosphoglycerate to 3-Phosphoglycerate
Purpose: Generate energy
Enzyme: Transferase (3-Phosphoglycerate kinase)
Biochemical process: Dephosphorylation
Free energy change: + 1.3 kj/mol
1 molecule of ATP per turn are produced
This reaction is reversible and spontaneous
What is the 8th reaction of glycolysis?
3-Phosphoglycerate to 2-Phosphoglycerate
Purpose: Reshuffle 3-Phosphoglycerate
Enzyme: Isomerase (Phosphoglycerate mutase)
Biochemical process: Isomerisation
Delta Go’ : + 4.4 kj/mol
Delta G: + 0.8 kj/mol
This reaction is reversible and spontaneous
The 9th reaction of glycolysis is?
2-Phosphoglycerate to phosphoenolpyruvate
Purpose: Form an ‘enol’
Enzyme: Lyase (Enolase)
Biochemical process: Dehydration
delta Go’ : + 1.8 kj/mol
delta G: - 1.1 kj/mol
Reaction occurs twice
Rxn is spontaneous and reversible
What is the 10th step of glycolysis?
Phosphoenolpyruvate to pyruvate
Purpose: Generate energy
Enzyme: Transferase (Pyruvate kinase)
Biochemical process: Dephosphorylation
delta Go’ : -31.4 kj/mol
delta G: -23.0 kj/mol
Rxn occurs twice; irreversible and non-spontaneous
This step is regulated by the energy in the cell. The higher the energy of the cell the more inhibited pyruvate kinase becomes.
Indicators of high energy levels within the cell are high concentrations of ATP, Acetyl-CoA, Alanine, and cAMP.
Picture of inhibition of phosphoenolpyruvate 9PEP).
What is the net yield of glycolysis?
The net yield of glycolysis is 2 ATP
The prepatory phase consumes 2 ATP and 4 ATP are produced. This yields 2 ATP.
2 NADH + H+ are also produced
The NADH + H+ are ultimately converted to five molecules of ATP by the electron transport chain
Picture of Phase II of glycolysis.
What is unique about the enzyme hexokinase?
Hexokinase is considered a ‘perfect enzyme’
This is because its Km is very low and it is working near its maximum velocity all the time
What are the three irreversible steps of glycolysis?
- hexokinase/ glucokinase
- phosphofructokinase 1
- pyruvate kinase
What are the allosteric regulators of phosphofructokinase?
- AMP
- ADP
- Pi
all signal low energy - F 2,6 BP (most potent activator, under hormonal control)
How does ATP inhibit phosphofructokinase?
Alters the Km for fructose
When ATP is high PFK1 will not have much activity until F6P becomes high, this means that G6P will accumulate and:
- inhbit hexokinase
- make glycogen
Explain why ATP and citrate are feedback inhibitors of PFK.
ATP and citrate inhibit PFK1 because they are signs of a high enery state.
There is no reason to continue glycolysis if there is already plently of ATP.
This prevents us from commiting too much of our carbon pool to acetyl CoA which cannot be used for glycolysis.
What are the 10 enzymes of glycolysis?
- hexokinase
- phosphoglucoisomerase
- phosphofructokinase
- aldolase
- triose phosphate isomerase
- glyceraldehyde 3- phosphase dehydrogenase
- phosphoglycerate kinase
- phosphoglycerate mutase
- enoalse
- pyruvate kinase
