3.3 Glycolysis and Kreb's Cycle

What are the stages of aerobic respiration?

- Glycolysis

- Link Reaction

- Kreb's Cycle

- Electron Transport Chain

Where does glycolysis occur?

Cytoplasm

Where does Kreb's Cycle occur?

Mitochondrial Matrix

Where does the electron transport chain occur?

inner membrane of mitochondria

Write the overall equation for respiration?

C₆H₁₂O₆ + 6O₂ —> 6CO₂ + 6H₂O + energy

What is glycolysis?

Breakdown of glucose in the cytoplasm

What does glycolysis generate?

Pyruvate, reduced NAD and ATP

Glycolysis occurs in both...

...aerobic and anaerobic respiration

Describe the first step in glycolysis?

Glucose is phosphorylated to form glucose-6-phosphate. This makes it more reactive and polar, to prevent diffusion out of the cell and to lower activation energy for enzyme controlled reaction to occur?

Describe the second step of gluycolysis to form fructose-1, 6-diphosphate

Glucose-6-phosphate is rearranged to isomer form fructose-6-phosphate. Phosphorylated again.

Describe third step in glycolysis to form phosphoglyceraldehyde

Fructose-6-diphosphate split into glyceraldehyde-3-phosphate (triose phosphate)

Why can't glycolysis occur in the mitochondrial matrix?

Sugars too big to pass through mitochondrial membranes to enter matrix. Plus enzymes for glucose breakdown are not present in the matrix

What happens in glycolysis after glyceraldehyde-3-phosphate is formed?

It is phosphoryated (by an iP not ATP) to form glycerate-1, 3-biphosphate. Simultaneously, 2 hydrogen atoms are produced to make space for the phosphate group. These H atoms combine with NAD and are taken to the ETC

What happens after glycerate-1, 3-biphosphate is produced in glycolysis?

It donates a P group to phosphorylate ADP to ATP by SLP. It does this a second time to produce another ATP and a H₂O molecule

How many molecules of ATP are produced in glycolysis under anaerobic conditions?

2

How many net ATP are produced in glycolysis under aerobic conditions?

4 ATP from SLP

6 ATP from ETC

2 ATP used

—————————

8 ATP net total

What is meant by dehydrogenation?

Removal of hydrogen from a molecule

What stage in glycolysis does dehydrogenation occur?

Dehydrogenation of glyceraldehyde-3-phosphate to form glycerate-1, 3-biphosphate

What is meant by decarboxylation?

Removal of a carboxyl group from a molecule, releasing carbon dioxide

Briefly describe the link reaction

Pyruvate enters matrix

Dehydrogenated and decarboxylated, releasing hydrogen (to form NADH₂) and CO₂

2 Carbon acetate group left over, combines with acetyl co-enzyme A (AcCoA) to enter Kreb's cycle

Equation for link reaction

pyruvate + NAD + AcCoA —> AcCoA + reduced NAD + CO₂

Which bonds are broken during respiration?

C-C

C-H

C-OH

During respiration, high energy bonds are broken to form...

Lower energy bonds, and the difference is released to attach iP to ADP to make ATP

Define aerobic respiration

The release of large amounts of energy, made available as ATP, from the breakdown of molecules, with oxygen as the terminal electron acceptor

Define anaerobic respiration

The breakdown of molcules in the absence of oxygen, releasing relatively little energy, making a small amount of ATP by substrate level phosphorylation

How is glyceraldehyde-3-phosphate converted to pyruvate?

By oxidation

Describe the basis of glycolysis

Glucose phosphorylated.

6C Hexose is split intoo two 3C triose phosphate molecules

3C phosphate molecules then oxidatised into pyruvate

Give the overall equation for glycolysis

Glucose + 2ATP + 2NAD + 2Pi —> 2 Pyruvate + 2red.NAD + 4ATP + heat energy

Describe the basis of the link reaction

Oxidative decarboxylation of the pyruvate to form acetyl coenzyme A

How many ATP molecules are generated from one glucose molecule during aerobic respiration?

38

Describe the full Kreb's cycle?

1. AcCoA combines with a 4C acid (oxaloacetate) to form 6C acid (citrate)

2. 6C acid decaroxylated and dehydrogenated releasing CO₂ and 2H. Water taken in. Forms 5C acid

3. 5C acid decaroxylated and dehydrogenated releasing CO₂ and 2H. Water taken in. Forms. 4C acid. ATP also synthesised here by substrate level phosphorylation

4. 4C acid dehydrogenated releasing 2H and water taken in. FAD used here

5. 4C acid dehydrogenated again. Water not taken in. NAD used here and 4C acid reformed to combine again with AcCoA

How many water molecules are taken in during water Kreb's cycle?

3H₂O

How many dehydrogenation reactions occur during Kreb's cycle?

4 dehydrogenation reactions

How many decarboxylation reactions occur during Kreb's cycle?

2 decarboxylation reactions

Explain why AcCoA doesn't accumulate during Kreb's cycle?

it is completely broken down and the 4C intermediate is regenerated\

What is produced from the Kreb's cycle?

1 ATP by Slp

3 NADH₂

2 CO₂

1 FADH₂

Importance of Kreb's cycle?

- provides reducing power for the ETC

- Allows different compounds to be metabolised and allows synthesis of new compounds from cycle intermediates

Define the ETC

Series of pumps, H and e⁻ carriers that span the inner mitochondria membrane (large SA=more carriers)