1. Cellular Respiration

2. What you should know
The role of ATP in the transfer of energy and the phosphorylation of molecules by ATP.
Metabolic pathways of cellular respiration. The breakdown of glucose to pyruvate in the cytoplasm in glycolysis, and the progression pathways in the presence or absence of oxygen (fermentation).
The role of the enzyme phosphofructokinase in this pathway.
The formation of citrate.
Pyruvate is broken down to an acetyl group that combines with coenzyme A to be transferred to the citric acid cycle as acetyl coenzyme A.
Acetyl coenzyme A combines with oxaloacetate to form citrate followed by the enzyme mediated steps of the cycle.
This cycle results in the generation of ATP, the release of carbon dioxide and the regeneration of oxaloacetate in the matrix of the mitochondria.
Dehydrogenase enzymes remove hydrogen ions and electrons which are passed to the coenzymes NAD or FAD to form NADH or FADH2 in glycolysis and citric acid pathways.
NADH and FADH2 release the high-energy electrons to the electron transport chain on the mitochondrial membrane and this results in the synthesis of ATP.
ATP synthesis — high-energy electrons are used to pump hydrogen ions across a membrane and flow of these ions back through the membrane synthesises ATP using the membrane protein ATP synthase. The final electron acceptor is oxygen, which combines with hydrogen ions and electrons to form water.

3. Introduction to Cellular Respiration
A series of metabolic pathways that brings about the release of energy from a foodstuff
In doing so it also regenerates the high-energy compound Adenosine Triphosphate (ATP)

4. ATP Adenosine Triphosphate Molecule able to provide energy immediately
Consists of Adenosine & 3 inorganic phosphate molecules
Energy held within ATP is released when the terminal phosphate is broken off (by enzymes)
adenosine Pi

5. ATP Adenosine Triphosphate This bond broken to release energy
Adenosine Diphosphate (ADP) and an inorganic phosphate are produced
Also, energy is required to regenerate ATP from ADP & Pi
adenosine Pi

6. ATP acts as the link between catabolic (energy releasing reactions) and anabolic (energy requiring reactions)
At any given moment some ATP molecules are undergoing breakdown (releasing energy), while others are being regenerated from ADP + Pi (using energy)
This means there is a
relatively fixed quantity
of ATP available

7. PHOSPHORYLATION
The addition of a phosphate group to a molecule, e.g. ADP + Pi = ATP
Phosphates can also be transferred from ATP to reactants in the pathway to make them more reactive
e.g. Glucose > Glucose- 6- Phosphate
Often a step in a pathway can only proceed if a reactant becomes phosphorylated
ATP
ADP

8. Importance of ATP formation
We all need energy to function and we get this energy from the foods we eat
The most efficient way for cells to harvest energy stored in food is through cellular respiration
a catabolic pathway for the production of adenosine triphosphate (ATP)
ATP, a high energy molecule, is expended by working cells
Cellular respiration occurs in both eukaryotic and prokaryotic cells

9. RESPIRATION
Process by which energy is released from foods by oxidation.
It involves the regeneration of ATP which is a high energy compound.
Consists of 3 stages
GLYCOLYSIS
CITRIC ACID CYCLE (KREBS CYCLE)
ELECTRON TRANSPORT CHAIN

10. GLYCOLYSIS Takes place in the cytoplasm of the cell.
Is a series of enzyme controlled steps
Glucose (6C) is broken down into two molecules of Pyruvic Acid (3C) (Pyruvate)
Does not require oxygen
Net gain of 2 ATP

11. Energy investment and payoff during glycolysis
Phosphorylation occurs twice. The 2nd time by phosphofructokinase
The first half of the chain makes up the energy investment phase- where 2 ATP are used per glucose molecule
The second half of the chain makes up the energy payoff phase-where 4 ATP are produced per glucose molecule

12. Phosphorylation during energy investment stage
The first phosphorylation of intermediates leads to a product that can continue to a number of other pathways
(E.g. fermentation in the absence of oxygen)
The second phosphorylation catalysed by phosphofructokinase is irreversible and leads only to the glycolytic pathway

13. Energy payoff stage
Hydrogen ions are released by the action of a dehydrogenase enzyme
Co-enzymes NAD and FAD pick up the H+ ions to form NADH or FADH in glycolysis and the citric acid pathways
NADH and FADH release high energy electrons to the electron transport chain on the mitochondrial membrane
Resulting in the synthesis of ATP

14. GLYCOLYSIS GLUCOSE PYRUVIC ACID 2 ATP 2 ADP+Pi 2 NAD 2 NADH2 4 ADP+Pi

15. MITOCHONDRIA Citric Acid Cycle takes place in the matrix
Electron Transport Chain takes place on the cristae

16. CITRIC ACID CYCLE Takes place in the matrix of the mitochondria.
Requires oxygen
Pyruvate/Pyruvic acid converted to Acetyl which then combines with Coenzyme A (2C)
Further Hydrogen ions are released and bind to NAD, forming NADH
Acetyl CoA combines with oxaloacetate a 4C compound to form 6C citrate
This stage involves the regeneration of oxaloacetate

17. CITRIC ACID CYCLE
Citrate is converted back to oxaloacetate by a series of enzyme controlled reactions.
During the cycle, carbon is released in the form of carbon dioxide, hydrogen is released and binds to NAD/FAD and ATP is formed.

18. CITRIC ACID CYCLE PYRUVIC ACID (3C) CO2 ACETYL COA (2C)
5C COMPOUND
4C COMPOUND
4C oxaloacetate
2NAD
2NADH2
CO2
2FAD
2FADH2
ADP+Pi
ATP
CO2
2NAD
2NADH2

19. ELECTRON TRANSPORT CHAIN
Takes place on the cristae of the mitochondria.
The reduced NAD/FAD transfer the high energy electrons to a chain of carriers called the cytochrome system
Energy from the electrons is used to pump H+ from the inner matrix to the intermembrane space
This maintains a higher conc of hydrogen ions in the intermembrane space, so..
The return flow of H+ ions rotates part of the membrane protein ATP synthase and ATP is generated
The final electron acceptor is oxygen which combines with hydrogen ions and low energy electron to form water

21. ELECTRON TRANSPORT CHAIN
The transfer of one H molecule releases 3 ATP molecules
This is called oxidative phosphorylation

22. ELECTRON TRANSFER SYSTEM
ADP +Pi
ADP +Pi
ADP +Pi
NADH2
WATER
SERIES OF HYDROGEN CARRIERS
NAD
OXYGEN
ATP
ATP
ATP

23. ATP PRODUCTION SUMMARY
Each NADH2 molecule produces 3 ATP
12 NADH2 = 36ATP from Kreb’s cycle
2 ATP from glycolysis
38 ATP in total

24. What you should know
Substrates for respiration. Starch and glycogen, other sugar molecules, amino acids and fats.
Regulation of the pathways of cellular respiration by feedback inhibition — regulation of ATP production, by inhibition of phosphofructokinase by ATP and citrate,
synchronisation of rates of glycolysis and citric acid cycle.
Energy systems in muscle cells.
Creatine phosphate breaks down to release energy and phosphate that is used to convert ADP to ATP at a fast rate. This system can only support strenuous muscle activity for around 10 seconds, when the creatine phosphate supply runs out. It is restored when energy demands are low.
Lactic acid metabolism. Oxygen deficiency, conversion of pyruvate to lactic acid, muscle fatigue, oxygen debt.
Types of skeletal muscle fibres
Slow twitch (Type 1) muscle fibres contract more slowly, but can sustain contractions for longer and so are good for endurance activities. Fast twitch (Type 2) muscle fibres contract more quickly, over short periods, so are good for bursts of activity.

25. Substrates for respiration
Starch and glycogen (carbohydrates) are broken down to glucose
Maltose and sucrose (carbohydrates) can be converted to glucose or glycolysis intermediates
Proteins can be broken down to amino acids and converted to intermediates of glycolysis and the citric acid cycle
Fats can be broken down into fatty acids and glycerol. Glycerol is converted to a glycolytic intermediate and fatty acids converted for use in the citric acid cycle

26. Regulation of Cellular Respiration
The cell conserves its resources by only producing ATP when required
Feedback inhibition regulates and synchronises the rates of the glycolytic and citric acid cycle pathways

27. If more ATP than the cell needs is produced the ATP inhibits phosphofructokinase slowing glycolysis
High concentrations of citrate also inhibit phosphofructokinase
When citrate concentration drops the enzyme is no longer inhibited

28. Energy systems in muscle cells
During strenuous muscle activity the cell breaks down its reserves of ATP and releases energy
Muscle cells can only store enough ATP for a few muscle contractions
Muscle cells have an additional source of energy

29. Energy systems in muscle cells
Creatine phosphate acts as a high energy reserve available to muscle cells during strenuous exercise
During strenuous exercise creatine phosphate breaks down releasing energy and phosphate which are used to convert ADP to ATP by phosphorylation

30. This system can only support strenuous muscle activity for around 10 seconds before the supply of creatine phosphate runs out
When ATP demand is low, ATP from cellular respiration restores the levels of creatine phosphate

31. Lactic acid metabolism
If strenuous exercise continues the cells respire anaerobically as they do not get enough oxygen
Neither the citric acid cycle nor electron transport system can generate the ATP required
Only glycolysis is able to provide more ATP
This results in pyruvate being converted to lactic acid
It involves the transfer of hydrogen from NADH produced during glycolysis to pyruvic acid to produce lactic acid
NAD is regenerated to maintain ATP production during glycolysis
Only 2 molecules of ATP are produced from each molecule of glucose
Lactic acid metabolism

32. As lactic acid builds in the muscles it causes fatigue
An oxygen debt builds up
When the oxygen debt is repaid, the lactic acid is converted back to pyruvic acid which then enters the aerobic pathway

33. ANAEROBIC RESPIRATION
Oxygen debt builds up
Glucose
(6C)
Pyruvic Acid
(2 X 3C)
Lactic Acid
(2 X 3C)
Oxygen debt repaid

34. AEROBIC V ANAEROBIC 38 2 Aerobic Respiration Anaerobic Respiration
Number of ATP molecules per glucose molecule 38 2
Products of reaction (other than ATP)
Carbon dioxide and water
Lactic acid
Location in cell
mitochondrion
cytoplasm

35. Types of skeletal muscle
Skeletal muscles bring about movement of the body
Two types of skeletal muscle fibres
Type 1- Slow Twitch Muscle Fibres
These contract slowly, but sustain contractions for longer
Good for endurance activities
Rely on aerobic respiration to generate ATP
Have many mitochondria
Have a large blood supply
Have a high concentration of myoglobin which is good at storing oxygen (myoglobin also extracts oxygen from the blood)
Major storage fuel is fats

36. Type 2- Fast Twitch Muscle Fibres
Muscle fibres contract quickly
Over short periods of time
Good for bursts of activity
Generates ATP through glycolysis
Have only a few mitochondria
Lower blood supply
Major storage fuels are glycogen and creatine phosphate

37. Most human muscle tissue contains both slow and fast twitch fibres
Athletes show distinct patterns of muscle fibres that reflect their sporting activities
Fast twitch fibres are responsible for strength. Sports requiring sudden bursts of maximum activity, such as in sprinting, throwing, jumping and lifting rely on fast twitch fibres.
Slow twitch fibres are responsible for stamina and suppleness. The action of slow twitch fibres is dependent on aerobic respiration. So, the supply of oxygen is important. The presence of large quantity of myoglobin is necessary. Therefore, slow twitch fibres give the characteristic red colour.