1. Cellular Respiration and Fermentation
Chapter 9
Unit 3

2. Catabolic Pathways Fermentation Cell Respiration
Partial breakdown of sugars
anaerobic
Cell Respiration
Most prevalent and efficient
Complete breakdown of sugars
aerobic

3. Redox Reactions: Oxidation and Reduction
Transfer of e- from one reactant to another
Oxidation: loss of electrons
Reduction: addition of electrons to another substance
Reducing agent: electron donor (C6H12O6)
Glucose reduces oxygen which accepts the e-
Oxidizing agent: electron acceptor (6O2)
Oxidizes glucose by accepting the e-
oxidation
C6H12O O2  6H2O + 6CO2
reduction

4. Energy Harvest via NAD+
Energy is released as electrons “fall” from organic molecules to O2
Broken down into steps:
Coenzyme NAD+ = electron acceptor
NAD+ picks up 2e- and 2H+  NADH (stores E)
NADH carries electrons to the electron transport chain (ETC)
ETC: transfers e- to O2 to make H2O ; releases energy

5. Substrate-Level Phosphorylation
Phosphorylation: enzyme transfers a phosphate from a substrate to ADPother compounds
Mode of ATP synthesis
ADP + Pi  ATP

6. Stages of Cellular Respiration
Glycolysis
Pyruvate oxidation and krebs
Oxidative Phosphorylation: ETC and chemiosmosis

7. Glycolysis “sugar splitting”
Believed to be ancient (early prokaryotes)
Occurs in cytosol
Partially oxidizes glucose (6C) to 2 pyruvates (3C)
Net gain: 2 ATP + 2NADH
Also makes 2H2O
Anaerobic

8. Occurs in two Phases
Energy-investment phase: uses two molecules of ATP (5 steps)
Energy yielding phase: produces four ATP molecules and reduces two molecules of NAD+ to NADH
The junction between Glycolysis and the Krebs cycle is the oxidation of pyruvate to acetyl CoA.
two acetyl fragments are produced

10. Mitochondrion Structure
Citric Acid Cycle
(matrix)
ETC
(inner membrane)

11. Oxidation of Pyruvate Eukaryote-> mitochondria
Prokaryotes-> cytosol
Pyruvate is converted to coenzyme A (acetyl CoA)

12. Krebs Cycle (Citric acid cycle)
Occurs in the mitochondrial matrix
aerobic
Completes glucose oxidation by breaking down acetyl CoA into 3 molecules of carbon dioxide
Net gain: 2 ATP, 6 NADH, 2 FADH2

14. Krebs cycle Evolution Evolved later than glycolysis
bacteria 3.5 billion years ago (glycolysis)
free O2 2.7 billion years ago (photosynthesis)
eukaryotes 1.5 billion years ago (aerobic respiration = organelles  mitochondria)
Hans Krebs

15. The Electron Transport Chain
electron-carrier molecules built into the inner mitochondrial membrane
Does not make ATP directly
Eases the fall of e- from food to oxygen
Oxygen final electron acceptor

16. Sequence of electron transfers along the electron transport chain

17. Chemiosmosis ATP production
This is accomplished by creating a proton gradient
ATP synthase
Cristae H+
ADP + Pi

18. How chemiosmosis works:
the electron transport chain creates the proton gradient by pumping H+ from the mitochondrial matrix
the membrane’s phospholipid bilayer is impermeable to H+s and prevents back flow
As protons diffuse through the ATP synthase complex phosphorylation of ADP occurs H+
ADP + Pi

19. Anaerobic Respiration
Prokaryotes who live in environments w/o Oxygen
Generate ATP using other electron acceptors besides O2
EX: sulfur reducing bacteria use sulfate ions at the end of their ETC
Hydrogen sulfide is produced
Rotten egg odor in salt marshes or mud flats

20. Types of Fermentation
Extension of glycolysis that allows continuous generation of ATP
Types:
Alcoholic Fermentataion:
Pyruvate is converted to ethanol
CO2 is released as it is converted to acetaldehyde
Acetaldehyde is reduced by NADH to ethanol
Regenerates NAD+ needed for glycolysis

21. Lactic Acid Fermentation
Pyruvate is reduced by NADH to form lactate as an end product
Lactate that accumulates in muscle cells was thought to cause muscle fatigue and pain, but now it is suggested that pain comes from increased levels of K+
Lactate appears to enhance muscle performance
Lactate is carried by the blood to the liver where it is converted back to pyruvate.

22. Anaerobes
Obligate Anaerobes: carry out fermentation or anaerobic respiration
Cannot survive in presence of Oxygen
EX: vertebrate brain cells cannot carry out fermentation
Facultative Anaerobes: use either fermentation or respiration
Consumes more sugar when fermenting than respiring to make same amt. of ATP
EX: yeast, bacteria, muscle cells

23. Glycolysis Fermentation Respiration
Without O2
O2 present
Fermentation
Respiration
Keep glycolysis going by regenerating NAD+
Occurs in cytosol
No oxygen needed
Creates ethanol [+ CO2] or lactate
2 ATP (from glycolysis)
Release E from breakdown of food with O2
Occurs in mitochondria
O2 required (final electron acceptor)
Produces CO2, H2O and up to 32 ATP