1. KEY AREA 7: Cellular Respiration
Higher Human Biology
Unit 1
Human Cells
KEY AREA 7: Cellular Respiration

2. Human Cells Learning Intentions
KEY AREA 7 – Cellular Respiration
Role of ATP
Metabolic Pathways of Cellular Respiration
Regulation of Cellular Respiration Pathways

3. 7a) Role of ATP
Cellular respiration is a series of metabolic pathways that releases energy from food and generates a high energy compound called adenosine triphosphate (ATP)
ATP is composed of adenosine and three inorganic phosphate (Pi) groups
Energy is released from ATP when the bond attached to the terminal phosphate is broken by enzyme action
ATP releases energy and breaks down to form Adenosine diphosphate (ADP) and inorganic phosphate (Pi)
ADP + Pi  ATP (this reaction is called Phosphorylation)

4. 7b) Role of ATP
ATP is very important as it acts as the link between catabolic energy releasing reactions (e.g. respiration) and anabolic energy-consuming reactions (e.g. protein synthesis)
There is a rapid turnover of ATP in a cell
ATP is continuously made at the same time as it is being used up, so there is no need for humans to have a vast store of ATP
Phosphorylation is an enzyme controlled process by which a phosphate group is added to a molecule
Phosphorylation also occurs when the phosphate and energy are transferred from ATP to the molecules of a reactant in a metabolic pathway, making them more reactive

5. 7c) Metabolic Pathways of Cellular Respiration
Cellular respiration is a series of metabolic pathways that releases energy from food and generates a high energy compound called adenosine triphosphate (ATP)
There are 3 stages involved in Cellular Respiration:-
Stage 1 – Glycolysis (occurs in the cytoplasm of a cell)
Stage 2 – Citric Acid Cycle (occurs in the central matrix of mitochondria)
Stage 3 – Electron Transport Chain (occurs in the inner membrane of mitochondria)

6. 7d) Glycolysis 1st Stage of Respiration
Occurs in the cytoplasm of a cell
Glucose  Pyruvate (enzyme controlled process)
Energy investment phase (2 ATP are needed for Glycolysis)
1st Phosphorylation produces an intermediate which can continue to other metabolic pathways
2nd Phosphorylation is catalysed by phosphofructokinase and is an irreversible reaction which can only lead to Glycolysis pathway
Energy payoff phase (4 ATP are produced)
Net gain of 2 ATP per molecule of glucose
Hydrogen ions are released from glucose by dehydrogenase enzyme
H+ ions are passed onto NAD forming NADH
No oxygen required for Glycolysis

7. 7e) Glycolysis

8. 7f) Citric Acid Cycle Citric Acid Cycle 2nd Stage of Respiration
Occurs in the central matrix of mitochondia
a) Formation of Citrate
Oxygen is required (aerobic respiration)
Pyruvate is broken down to an Acetyl Group that combines with Coenzyme A (Acetyl Coenzyme A)
H+ ions are released and bind to NAD forming NADH
Carbon Dioxide is released
Acetyl Coenzyme A + Oxaloacetate  Citrate
b) The Citric Acid Cycle
Occurs in the central matrix of the mitochondria
Citric Acid Cycle involves many enzyme controlled steps which results in:-
- Regeneration of Oxaloacetate
- Release of Carbon Dioxide
- Generation of ATP
Dehydrogenase enzymes remove H+ ions and high energy electrons and pass them
to NAD to make NADH, and FAD to make FADH2

9. 7g) Citric Acid Cycle

10. 7h) Electron Transport Chain
3rd Stage of Respiration
Occurs in the inner membrane of mitochondia
The electron transport chain consists of protein molecules found attached to the inner membrane of the mitochondria
NADH and FADH2 from Glycolysis and the Citric Acid pathways release high-energy electrons to the electron transport chain on the mitochondrial membrane and this results in the synthesis of the bulk of ATP
ATP synthesis
High energy electrons are used to pump hydrogen ions across a membrane and flow
these ions back through the membrane synthesising ATP using the membrane protein ATP synthase
Final electron acceptor is oxygen
Oxygen combines with hydrogen ions and electrons to form water

11. 7i) Electron Transport Chain

12. 7j) Substrates for Respiration
Fate
Starch & Glycogen
Broken down into Glucose and feed into the GlycolyticPathway
Other Sugars
(e.g. maltose, sucrose) – converted to glucose and feed into the Glycolytic Pathway
Fats
broken down into Fatty Acids & Glycerol. Glycerol feeds into the Glycolytic Pathway, and the Fatty Acids enter the pathway as Acetyl Coenzymes A for use in the Citric Acid Cycle
Proteins
Amino Acids are de-aminated forming intermediates that can enter the respiratory pathway as pyruvate, acetyl coA, or intermediates of the Citric Acid Cycle

13. 7k) Regulation of Cellular Respiration Pathways
The cell conserves its resources by only producing ATP when required
As the rate of glycolysis and the citric acid cycle increases, ATP supply increases
As the rate of glycolysis and the citric acid cycle decreases, ATP supply decreases
If a cell produces more ATP than it needs, the high concentration of ATP inhibits phosphofructokinase, and slows down the rate of glycolysis
When the concentration of ATP decreases, the enzyme is no longer inhibited and glycolysis speeds up
The rate of glycolysis and the rate of the citric acid cycle are synchronised by the inhibition of phosphofructokinase by citrate
If citrate accumulates, glycolysis slows down
If citrate consumption increases, glycolysis increases the supply of acetyl groups to the citric acid cycle

14. 7l) Regulation of Cellular Respiration Pathways

15. Human Cells Questions KEY AREA 7 – Cellular Respiration
Testing Your Knowledge 1 Page Q’s 1-3
2. Quick Quiz