1. RESPIRATION
The stepwise breakdown of glucose to carbon dioxide and water to release energy

2. Aerobic respiration References: Rowland pages 120 - 132
Collins pages
Aerobic respiration
glucose + oxygen carbon dioxide and water + energy
C6H12O6 + 6O CO2 + 6H mols ATP
A great deal of energy is released when glucose is oxidised to carbon dioxide and water in the presence of oxygen. If all this energy was released in one go, as it is in combustion, it would damage the cell.
It is released in a stepwise catabolism of glucose to release usable amounts of energy to produce ATP

3. ATP ATP ADP + P + energy for all cell activities
ATP - adenosine triphosphate = adenosine P - P - P
ADP - adenosine diphosphate = adenosine P - P
ADP + P ATP
ATP ADP + P + energy for all cell activities

4. Oxidation and reduction (redox)
Three ways in which oxidation and reduction occurs in respiration
Direct involvement of oxygen
A + O2 AO (oxidation = addition of oxygen)
AO A + O (reduction = removal of oxygen)
Removal/addition of hydrogen
AH A + H (oxidation = removal of hydrogen)
A + H AH (reduction = addition of hydrogen)
Removal/addition of electrons
Ae- A + e- (oxidation = removal of electrons)
A + e- Ae- (reduction = addition of electrons)

5. Hydrogen carriers
Oxidation of substrates in respiration often involves the removal of hydrogen atoms (dehydrogenation) and is important in the synthesis of ATP.
With the help of a dehydrogenase enzyme, hydrogen atoms are removed from a compound and taken up by a hydrogen carrier (acceptor)
There are two types of hydrogen carriers in respiration:
NAD nicotinamide adenine dinucleotide
FAD flavine adenine dinucleotide
AH2 NAD BH2
A NADH + H+ B

6. Aerobic respiration can be divide into 4 stages
Glycolysis takes place in the cytoplasm
Link reaction
Krebs cycle take place in the mitochondria
Electron transport chain
Total yield of ATP from one molecule of glucose = 38ATP

7. GLYCOLYSIS Takes place in cytoplasm Does not need oxygen
Each glucose molecule yields 2 ATP molecules
Common to both aerobic and anaerobic respiration
Glycolysis represents a series of reactions in which one molecule of
glucose is broken down into 2 molecules of pyruvate.
3 main steps:
Phosphorylation of glucose(6C) to form fructose diphosphate (6C)
Fructose diphosphate split into two molecules of 3C sugars
Conversion of two 3C sugars into two molecules of pyruvate (3C)
Net gain of 2 ATP and 2 NADH + H+

8. Glycolysis Read textbook references Rowland pages122 – 125
Collins page 11-12
Make notes on glycolysis

9. What happens next? If no oxygen is available:
Pyruvate is converted (reduced) to lactate by accepting hydrogen from NADH
There is no further production of ATP, so net gain of anaerobic respiration is 2 ATP from 1 molecule of glucose
If oxygen is available:
Pyruvate enters the mitochondria and will be fully oxidised to carbon dioxide and water and 38ATP produced
The mitochondrion is the site of the Link Reaction, the Krebs Cycle and the Electron Transport Chain

10. Into the mitochondrion
Need to know the structure of a mitochondrion and to be able to recognise electronmicrographs; see Core Principles
The Link Reaction and the Krebs Cycle occur in the matrix of the mitochondrion
The Electron Transport Chain takes place on the membranes of the cristae
The cristae are highly folded to increase the surface area for the reactions to take place

11. The Link Reaction
The Link Reaction links glycolysis to the Krebs Cycle.
Oxygen is needed for the process
It occurs in the matrix of the mitochondrion
The products are all x 2 as there are 2x pyruvates which enter the Link Reaction

12. So what happens?
Pyruvate enters the mitochondria (the inner mitochondrial membrane is impermeable to glucose and other intermediates)
The 3-carbon pyruvate combines with the carrier molecule
coenzyme A (CoA)
It forms a 2-carbon compound called acetyl coenzyme A (acetylCoA)
The extra carbon is lost as carbon dioxide.
NAD+ removes hydrogen to form reduced NAD (NADH +H+)
The process is therefore called oxidative decarboxylation

13. The Krebs Cycle Oxygen is needed for the process to occur
It takes place in the matrix of the mitochondrion
The cycle goes round twice for every molecule of glucose oxidised; the products are, therefore, all x2
It is where most of the oxidation takes place in aerobic respiration
It results in the complete breakdown of pyruvate to carbon dioxide and water

14. So what happens?
Acetyl coenzyme A enters the cyclic series of reactions called the Krebs Cycle
The 2-carbon acetyl part of the molecule joins up with a 4-carbon acceptor molecule to form a 6-carbon acid
There are 2 decarboxylations to regenerate the 4-carbon acceptor molecule and to release 2 molecules of carbon dioxide
Hydrogens and electrons are removed at 4 points in the cycle; involves NAD+ at three points and FAD at one point
One molecule of ATP is produced for each turn of the cycle; called substrate level phosphorylation

15. Result Glycolysis 2NADH 2ATP Link Reaction 2NADH 2CO2
At the end of glycolysis, the Link Reaction and Krebs Cycle for every
glucose molecule oxidised:
Glycolysis 2NADH 2ATP
Link Reaction 2NADH 2CO2
Krebs Cycle 6NADH 2ATP 4CO2
2FADH2
So where are the 38 ATP molecules?
Don’t miss next week’s exciting instalment!

16. Link Reaction and Krebs Cycle
Read textbooks and make notes on Link Reaction and Krebs Cycle
Rowland page 124 onwards
Roberts page 101 onwards
Collins page 12-13

17. Electron Transport Chain
Oxygen is needed
Takes place in the phospholipid bilayer of the inner mitochondrial membranes - the cristae
Reduced coenzymes NAD (NADH + H+) and FAD (FADH2) are re-oxidised to release large amounts of ATP
34 molecules of ATP are produced from the oxidation of the reduced coenzymes

18. So what happens?
Reduced NAD and FAD are reoxidised by the removal of hydrogen by dehydrogenase enzymes located on the cristae of the inner membrane of the mitochondrion.
Each hydrogen atom is split into a hydrogen ion (H+) and an electron (e-)
The electrons then pass from one electron carrier molecule to another electron carrier molecule;
Electron carrier molecules in the ETC are called cytochromes and are proteins embedded in the cristae membranes
The electron carrier molecules are at successively lower energy levels

19. And more ……
As the electrons are transferred from one carrier to another some of their energy is released and used to convert ADP into ATP
One molecule of ATP is formed every time an electron is transferred from one carrier to the next
The removal of hydrogen ions and electrons is oxidation and so the overall reactions of the ETC are known as oxidative phosphorylation
Finally, each electron is reunited with a hydrogen ion (H+) which immediately combines with oxygen to form water

20. ETC - even more detail!
As the electrons are passed from one electron carrier to
another, the energy released is used to actively pump hydrogen ions (H+ - protons) from the matrix into the space between the inner and outer membranes of the mitochondrion
Hydrogen ions accumulate and this sets up a large hydrogen ion gradient with a higher concentration of H+ in the inter-membrane space than in the matrix; this makes it more positively charged.
Hydrogen ions can only diffuse back down the concentration and electrical gradients through large protein carrier molecules which span the membrane, called ATP synthases
As H+ ions pass through the enzyme, it catalyses the synthesis of ATP from ADP and Pi

21. And finally …..
The passage of a pair of electrons from one reduced NAD molecule along the ETC provides enough energy to move sufficient hydrogen ions to produce 3 molecules of ATP
As the first electron carrier is FAD, the passage of electrons from reduced FAD results in the production of only 2 ATP molecules
The final carrier in the chain transfers the electrons to 2 oxygen atoms. Each of these oxygen atoms picks up two protons (H+ ions) to produce a molecule of water
2e- + 2H+ + O —> 2H2O
The enzyme cytochrome oxidase catalyses this last reaction involving oxidation by oxygen; it is inhibited by the poison cyanide

22. How much ATP is produced?
Calculate the number of ATPs produced by these processes:
a) Substrate level phosphorylation
glycolysis =
Krebs Cycle =
b) Oxidative phosphorylation
re-oxidation of 10 NADH along 3ATPs a go
re-oxidation of 2 FADH2 along 2ATPs a go
Total 2 2 30 4 38

23. Electron Transport Chain
Read and make additional notes from
Rowland pages
Collins page 14
Roberts pages