1. 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 acetate is combined with coenzyme A to be carried to the next stage;
explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs;

2. Respiration: The 4 Parts
Respiration consists of 4 parts:
Glycolysis
Link Reaction
Krebs Cycle
Oxidative Phosphorylation (the electron transport chain)

3. The Krebs Cycle is the Third Stage of Aerobic Respiration
The krebs cycle takes place in the matrix of the mitochondria.
It happens once for each pyruvate molecule made in glycolysis, and so it goes round twice for every glucose molecule that enters the respiration pathway

4. The Krebs Cycle Acetyl CoA 2C ATP 4- carbon compound oxaloacetate
ADP + Pi
CoA
NADH 4C
6- carbon compound
citrate
NAD 6C
FADH
The Krebs Cycle
FAD
CO2 1C
NAD
5- carbon compound
NADH
NAD
NADH 5C
CO2 1C

5. The Krebs Cycle
Acetyl co enzyme A from the link reaction combines with oxaloacetate to form citrate
Coenzyme A is released back to the link reaction to be used again
The 6-carbon citrate molecule is decarboxylated (loses CO2) to give a 5-carbon molecule
Both citrate and the 5-carbon molecule formed from it are also dehydrogenated (lose hydrogen) in the cycle, to reduce the coenzymes NAD and FAD (flavin adenine dinucleotide)

6. The Krebs Cycle
Overall, 3 reduced NAD+ and 1 reduced FAD are produced. These coenzymes can now be used to carry the hydrogen to the electron transport chain
The 5 carbon compound is decarboxylated, bringing you back to 4-carbon oxaloacetate. ATP and CO2 are released

7. 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

8. Products of the Krebs Cycle enter the final Stage of Aerobic Respiration
One coA is reused in the next link reaction
Oxaloacetate is regenerated so it can be reused in the next krebs cycle
Two carbon dioxide molecules are released as a waste product of respiration
One molecule of ATP is made per turn of the cycle- by substrate level phosphorylation
Three reduced NAD and one reduced FAD co-enzymes are made and enter the electron transport chain
Substrate-level phosphorylation is a type of chemical reaction that results in the formation and creation of adenosine triphosphate (ATP) by the direct transfer and donation of a phosphoryl (PO3) group to adenosine diphosphate (ADP)

9. 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

10. 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

11. Task
Now try to draw glycolysis, the link reaction and the Krebs Cycle on A3 with no notes 