MCB Lec 16 - REVISED

i hate glycolysis https://www.youtube.com/watch?v=UBudWWUqAmc this helps

Glycolysis

- 1 glucose —> 2 pyruvate

- nets 2 ATP

- catabolic and anaerobic

Glycolysis overall reaction

Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O

Stage 1 glycolysis

Energy Investment Stage

• traps glucose in the cell and modifies it so that it can be cleaved into a pair of phosphorylated 3-C compounds

• 2 ATP are “invested” to couple unfavorable reactions (steps 1 and 3 - the irreversible reactions)

Stage 2 Glycolysis

Energy Harvesting Stage

• oxidizes the 3-carbon compounds to pyruvate while generating a NET of 2 ATP

Enzymes accelerate chemical reactions using

acid-base, covalent, and metal ion catalysis.

Which coenzymes pick up electrons from compounds being oxidized?

NAD+, FAD, and ubiquinone

Larger negative change in free energy of a reaction can be coupled with

an unfavorable reaction

Breaking a phosphoanhydride bond in ATP requires….

lots of energy

First Stage of Glycolysis steps

1. Hexokinase - transferase

2. Phosphoglucose isomerase - isomerase

3. Phosphofructokinase - transferase

4. Aldose - lyase

5. Triose Phosphate Isomerase - isomerase

1. Hexokinase

Type, Reaction, Reversibility, What it does, important

Type of reaction: transferase

• transfer the phosphate group

Reaction:

glucose + ATP → glucose-6-phosphate + ADP

● IRREVERSIBLE

What is does: Substrate binding induced fit is used to minimize hydrolysis of ATP

Important: Requires a cofactor of Mn2+ or Mg2+

2. Phosphoglucose isomerase

Type, Reaction, Reversibility, What it does, important

Type of reaction: isomerase (Aldose to ketose)

reaction:

Glucose-6-phosphate —> Fructose-6-phosphate

• Crucial reaction because G6P is not readily cleaved into two 3-C fragments, while F6P is

• main goal of energy investment stage is to get a pair of 3-C compounds

3. Phosphofructokinase (PFK)

Type, Reaction, Reversibility, What it does, important

Type of reaction: Transferase

Reaction:

Fructose-6- phosphate —> Fructose-1,6- bisphosphate

● IRREVERSIBLE

• Traps the carbohydrate in the fructose form by the addition of a second phosphate group

• RATE DETERMINING STEP - slow step

• Allosteric enzyme through induced fit

• Fructose-2,6-bisphosphate is the main activator of PFK in mammals

KEY REGULATOR OF GLYCOLYSIS

4. Aldose

Type, Reaction, Reversibility, What it does, important

Type of reaction: Lyase

Reaction:

Fructose1,6-bisphosphate —> Glyceraldehyde-3- phosphate + DHAP

5. Triose Phosphate

Type, Reaction, Reversibility, What it does, important

Type of reaction: Isomerase

Reaction:

DHAP —> Glyceraldehyde-3- phosphate

• DHAP must be converted to G3P to enter stage 2

Important

• Catalytically perfect enzyme - catalysis occurs every time the substrate and enzyme meet

  • Acid-base catalysis

Try and replicate the first stage of glycolysis

Second Stage of Glycolysis:

oxidizes the 3-carbon compounds to pyruvate whole generating two molecules of ATP

Second Stage of Glycolysis steps

6. Glyceraldehyde 3-phosphate dehydrogenase - redox

7. Phosphoglycerate Kinase - Transferase

8. Phosphoglycerate Mutase - Isomerase

9. Enolase - Lyase

10. Pyruvate Kinase - Transferase

6. Glyceraldehyde 3-phosphate dehydrogenase

Type, Reaction, Reversibility, What it does, important

Type of reaction: REDOX

Reaction

G3P + NAD+ (oxidant) + Pi —> 1,3-Bisphosphoglycerate + NADH (reductant) + H+

• Oxidation of aldehyde to a carboxylic acid using NAD+

• Joining the carboxylic acid and orthophosphate to form the acyl-phosphate product

Important

• 1,3-BPG has higher phosphoryl transfer potential than ATP - can be used to synthesize ATP

7. Phosphoglycerate Kinase

Type, Reaction, Reversibility, What it does, important

Type of reaction: Transferase

Reaction:

1,3-BPG + ADP —> 3-Phosphoglycerate + ATP

• Substrate level phosphorylation

• Happens twice, meets the ATP investment

8. Phosphoglycerate Mutase

Type, Reaction, Reversibility, What it does, important

Type of reaction: isomerase

Reaction:

3- Phosphoglycerate —> 2- phosphoglycerate

• Enzyme is both kinase & phosphatase in route to the OVERALL isomerization

Important

• Phospho-Histidine used to transfer the phosphate group from the 3 position to the 2 position

9. Enolase

Type, Reaction, Reversibility, What it does, important

Type of reaction: Lyase

Reaction:

2- Phosphoglycerate —> Phosphoenolpyruvate, H2O

Phosphoenolpyruvate has high phosphoryl-transfer potential (can create ATP)

• Presence of the phosphate traps compound in an unstable enol tautomer (readily reactive)

10. Pyruvate Kinase

Type, Reaction, Reversibility, What it does, important

Type of reaction: Transferase

Reaction:

Phosphoenolpyruvate + ADP —> Pyruvate + ATP

● IRREVERSIBLE

• Enol to ketone conversion drives the reaction

Second of two substrate level phosphorylation steps in glycolysis

• ADP is substrate

Fates of Pyruvate

- Oxidation of glucose to pyruvate requires NAD+

- NAD+ is regenerated by further oxidation of pyruvate to CO2 (presence of oxygen) or in fermentation of ethanol of lactate (no oxygen)

Fermentation

anaerobic ATP-generating pathways in which electrons are removed from one organic molecule and passed to another

• Alcohol Fermentation

• Lactic acid fermentation

Alcohol Fermentation

glucose to ethanol

Pyruvate carboxylase catalyzes the decarboxylation of pyruvate - Alcohol dehydrogenase reduces the acetaldehyde to ethanol, regenerating NAD+

Enzymes:

• pyruvate decarboxylase

• alcohol dehydrogenase

Lactic Acid Fermentation:

- Conversion of glucose into two molecules of lactate

Enzyme: Lactate dehydrogenase

● REVERSIBLE

● Liver uses NAD+ to regenerate pyruvate from lactate

Entry of fructose in glycolysis

• Fructose

  • Fructose 1-phosphate pathway (liver)

  • Phosphorylated into hexokinase (adipose tissue)

The creation of GAP and DHAP through the fructose 1- phosphate pathway allows it to enter into the glycolysis pathway in the liver

Fructose in adipose tissue can enter glycolysis at Fructose-6P step

Entry of galactose in glycolysis

• Galactose

  • Converted to 6-phosphate by the galactose-glucose interconversion pathway

  • Galactose is phosphorylated by galactokinase

  • G1P is converted into glucose 6-phosphate by phosphoglucomutase

• Glucose 1-phosphate is generated using UDPglucose, a transferase, and an epimerase

• Galactose 1-phosphate uridyl transferase is mostly mutated in galactosemia