Glycolysis Flashcards by Daryl Traylor

Picture of the overview of glycolysis.

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Second picture of overview of glycolysis.

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Linear layout of glycolysis.

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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

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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

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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

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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.

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Picture showing the control of the committed step (Fruuctose-6-phosphate to Fructose-1,6-bisphosphate) of glycolysis.

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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

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Picture of 4th reaction of glycolysis.

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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

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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.

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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

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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

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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

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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 G^o’ : + 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 G^o’ : + 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 G^o’ : -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 K_m 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?

1. AMP 2. ADP 3. Pi all signal low energy 4. 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: 1. inhbit hexokinase 2. 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?

1. hexokinase 2. phosphoglucoisomerase 3. phosphofructokinase 4. aldolase 5. triose phosphate isomerase 6. glyceraldehyde 3- phosphase dehydrogenase 7. phosphoglycerate kinase 8. phosphoglycerate mutase 9. enoalse 10. pyruvate kinase