1. Watch the link from 4 minutes

2. Krebs Cycle
State that the Krebs cycle takes place in the mitochondrial matrix;
Outline the Krebs cycle, with reference to the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate (names of intermediate compounds are not required);
Explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs;

3. Summary of the Krebs Cycle
The Krebs cycle is a sequence of reactions, all of which are catalysed by enzymes present in the mitochondrial matrix.
Each 2C acetyl CoA + 4C= 6C
Circular pathway that results in production of original 4C compound
Reaction produces:
2x carboxylation =2 CO2
4x dehydrogenation: removal of pairs of hydrogen atoms (8 hydrogen atoms per 1 turn!) Taken up by coenzymes NAD (3 pairs) and FAD (1 pair)...go into electron transport chain
Substrate level phosohorylation =1xATP

5. The Krebs Cycle
The acetate from Acetyl co enzyme A from the link reaction combines with oxaloacetate (4C) to form citrate
Coenzyme A is released back to the link reaction to be used again
Citrate is decarboxylated (loses CO2) and dehydrogenated to form a 5C compound (reduced NAD)
The 5C compound is decarboxylated and dehydrogenated to produce a 4C compound and another molecule of reduced NAD
4C converted to another 4C- substrate level phosphorylation x1 ATP

6. 6. The second 4C converted to another 4C compound
6. The second 4C converted to another 4C compound. A pair of hydrogen atoms are removed and accepted by FAD 7. The third 4C compound is dehydrogenated and produces a molecule of NAD reduced and regenerates oxaloacetate.

7. THINK...
How many molecules of ATP, reduced NAD, reduced FAD and carbon dioxide will be produced from one molecule of glucose?
ANS = ATP molecules, 6 reduced NAD, 4 carbon dioxide and 2 reduced FAD
Why?
Because glucose produces two pyruvate compounds which will both go through the Krebs cycle

8. Task
Complete the Krebs cycle summary sheet

9. Products of the Krebs Cycle enter the final Stage of Aerobic Respiration
Some products are reused, some are released and others are used in the final stage, oxidative phosphorylation: the electron transport chain…
There is one turn of the Krebs cycle for each molecule of acetate, which was made from one molecule of pyruvate. Therefore there are two turns of the cycle for each molecule of glucose

10. This will be looked at next – the last stage Oxidative Phosphorylation
All the molecules of reduced electron carriers (NADH and FADH2) produced both by glycolysis and the Krebs Cycle are reoxidised in the electron transport chain.
During this process, a large amount of free energy is liberated, which can be used to generate ATP.
The enzymes for this are fixed in the folded inner membrane of the mitochondria
This will be looked at next – the last stage
Oxidative Phosphorylation

11. Krebs Questions
Why do living organisms only have a small amount of oxaloacetate in their cells?
Explain why each stage of the Krebs cycle needs to be catalysed by its own specific enzyme
State the role of pyruvate dehydrogenase

12. Krebs Questions
Why do living organisms only have a small amount of oxaloacetate in their cells? It is constantly being regenerated
Explain why each stage of the Krebs cycle needs to be catalysed by its own specific enzyme each substrate needs it’s own enzyme with a specifically shaped active site that is complementary to the substrate
State the role of pyruvate dehydrogenase it removes hydrogen from pyruvate

13. Tasks Complete the Krebs cycle summary sheet 1 and or 2
Now try to draw glycolysis, the link reaction and the Krebs Cycle onto A3 with no notes
Exam questions: None in booklet!!
Complete others…