1. Chapter 8 BIOL1000 Dr. Mohamad H. Termos
Cellular Respiration
Chapter 8
BIOL1000
Dr. Mohamad H. Termos

2. Biology, 9th ed,Sylvia Mader
Chapter 08
Cellular Respiration
Breaks down nutrient molecules for the production of ATP
Consumes oxygen and produces carbon dioxide (CO2)
Aerobic -
Usually involves the breakdown of glucose to CO2 and H2O
Energy is extracted from the glucose molecule:
Released step-wise
Allows ATP to be produced efficiently
Cellular Respiration

3. Glucose Catabolism Three major pathways of glucose catabolism
Glycolysis
Glucose (6 C)  two pyruvic acid molecules (3 C)
Anaerobic fermentation
Occurs in the absence of oxygen
pyruvic acid  lactic acid
Aerobic respiration
Occurs in the presence of oxygen
pyruvic acid  CO2 and H2O

4. Biology, 9th ed,Sylvia Mader
Chapter 08
Cellular Respiration
Cellular respiration includes four phases:
Glycolysis
Preparatory (prep) reaction
Citric acid cycle
Electron transport chain (ETC)
Many steps in each phase
NAD+ and FAD accept electrons to be transferred to other phases for more energy
Cellular Respiration

5. Glucose Catabolism
Two coenzymes of special importance to glucose catabolism
NAD+ (nicotinamide adenine dinucleotide)
Derived from niacin (B vitamin)
NAD+ + 2 H  NADH + H+
FAD (flavin adenine dinucleotide)
Derived from riboflavin
FAD + 2 H  FADH2

6. Outside the Mitochondria: Glycolysis
Biology, 9th ed,Sylvia Mader
Chapter 08
Outside the Mitochondria: Glycolysis
Glycolysis occurs outside mitochondria
Two ATP are used
Glucose  Pyruvate (3 carbon molecule)
Gain two NADH
Four ATP are produced; 2 are consumed
Net gain of two ATP (4 ATP produced - 2 ATP consumed)
Cellular Respiration

7. Outside the Mitochondria: Fermentation
Biology, 9th ed,Sylvia Mader
Chapter 08
Outside the Mitochondria: Fermentation
Pyruvate is a “biological crossroads”
If O2 is available to the cell, pyruvate enters the mitochondria for aerobic respiration.
If O2 is not available to the cell, fermentation (anaerobic process) occurs in the cytoplasm.
Cellular Respiration

8. Anaerobic Fermentation
In an exercising muscle, demand for ATP may exceed the oxygen supply
The only ATP cells can make under these circumstances are the 2 ATP produced by glycolysis
Glycolysis cannot continue without supply of NAD+
NADH donates a pair of electrons to pyruvic acid reducing it to lactic acid
Lactic acid leaves the cells
Enter bloodstream and transported to the liver
When oxygen becomes available the liver oxidizes it back to pyruvic acid
Oxygen is created by exercising muscle

9. Anaerobic Fermentation
Drawbacks of anaerobic fermentation
Wasteful, because most of the energy of glucose is still in the lactic acid and has contributed no useful work
Lactic acid is toxic and contributes to muscle fatigue
Skeletal muscle is relatively tolerant of anaerobic fermentation, cardiac muscle less so
The brain employs no anaerobic fermentation

10. Aerobic Respiration
Most ATP generated in mitochondria, which requires oxygen. In the presence of oxygen, pyruvic acid enters the mitochondria

11. Inside the Mitochondria
Biology, 9th ed,Sylvia Mader
Chapter 08
Inside the Mitochondria
The Preparatory (prep) Reaction: Connects glycolysis to the citric acid cycle. Pyruvate, enters the mitochondria. Pyruvate (3 carbons)  2-carbon group (Carbon dioxide released and electrons are picked up as hydrogen atom by NAD+ )
Citric Acid Cycle (Krebs cycle): Occurs in mitochondria. NADH and FADH2 capture energy rich electrons and ATP is formed. Produces: 4 CO2, 2 ATP, 6 NADH and 2 FADH2 per glucose molecule
Cellular Respiration

12. Inside the Mitochondria
Biology, 9th ed,Sylvia Mader
Chapter 08
Inside the Mitochondria
Electron Transport Chain (ETC): Takes place in the mitochondria. Receives electrons from NADH & FADH2 and produces ATP.
Oxygen serves as the final electron acceptor and combines with hydrogen ions to form water.
ATP moves out of mitochondria and is used for cellular work. It can be broken down to ADP and inorganic phosphate. These molecules are returned to the mitochondria for more ATP production
Cellular Respiration

13. Inside the Mitochondria
Biology, 9th ed,Sylvia Mader
Chapter 08
Inside the Mitochondria
Energy yield from glucose metabolism:
Net yield per glucose: 1- From glycolysis – 2 ATP, 2-From citric acid cycle – 2 ATP, 3- From electron transport chain – 32 or 34 ATP
Energy content: 1- Reactant (glucose) 686 kcal, 2- Energy yield (36 ATP) 263 kcal
The rest of the energy from glucose is lost as heat
Cellular Respiration

14. The Metabolic Pool Concept
Biology, 9th ed,Sylvia Mader
Chapter 08
The Metabolic Pool Concept
Cellular Respiration