1. How Cells Harvest Chemical Energy
CELLULAR RESPIRATION
How Cells Harvest Chemical Energy

2. CELLULAR RESPIRATION
Cellular Respiration is the process animals use to turn food (glucose) into energy (ATP).
The reactants of this reaction are glucose and oxygen.
The products are carbon dioxide, water, and energy (ATP).
Glucose = C6H12O6

3. THE EQUATION The overall equation for cellular respiration is:
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
In words:
Glucose + Oxygen  Carbon Dioxide + Water + Energy

4. THE EQUATION Where do we get glucose from? Food!
Where do we get oxygen from?
Breathing!
What do we breathe out?
Carbon Dioxide and Water!

5. THE REACTION
Cellular Respiration is an AEROBIC process, which means that it only happens when OXYGEN is present.
It happens in 3 stages: Glycolysis, the Kreb’s Cycle, and the Electron Transport System.

6. STEP 1: GLYCOLYSIS
Glycolysis breaks down glucose (6 carbons) into 2 molecules of pyruvic acid (with 3 carbons each)
It occurs in the cytoplasm of cells. (10 steps)
2 ATP are produced from each molecule of glucose.
It also produces 2 NADH, which is an organic molecule that carries electrons (energy)

7. 6.9 GLYCOLYSIS HARVESTS CHEMICAL ENERGY BY OXIDIZING GLUCOSE TO PYRUVIC ACID
Figure 6.9A

8. STEP 2: THE KREB’S CYCLE
Pyruvic acid diffuses into the inner matrix of the mitochondria, the location of the Kreb’s Cycle.
Pyruvic acid is converted into Carbon Dioxide (1 carbon) and Acetyl COA in the transition step (an enzyme with 2 carbons). It then becomes CO2, which we breathe out.
Each acetyl CoA is rearranged (oxidized) to release energy.
The Kreb’s Cycle produces 2 ATP, 6 NADH, and 2 FADH2.

9. 6.11 THE KREB’S CYCLE
Acetyl CoA
The Krebs cycle is a series of reactions in which electrons are transferred to NADH and FADH2 2
KREBS CYCLE
CO2
Figure 6.11A

10. STEP 3: THE ELECTRON TRANSPORT SYSTEM (ETS)
It is also called chemiosmosis, ETS, or ETC
It consists of a series of reactions on the cristae, the inner membrane of the mitochondria.
Electrons are released from NADH and FADH2, which release energy (called chemiosmosis).
Hydrogen ions are pumped across the membranes in the mitochondria.
Then they are pushed back through proteins, and ATP is synthesized.
34 ATP are produced during this part of the reaction.

11. ELECTRON TRANSPORT CHAIN
Chemiosmosis in the mitochondrion
Protein complex
Intermembrane space
Electron carrier
Inner mitochondrial membrane
Electron flow
Mitochondrial matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Figure 6.12

12. LET’S REVIEW
Glycolysis: Where does it occur? How many ATP are produced?
Kreb’s Cycle: Where does it occur? How many ATP are produced?
ETS: Where does it occur? How many ATP are produced?
Where does the carbon from glucose go? Where does the oxygen turn into?

13. An overview of cellular respiration
High-energy electrons carried by NADH
GLYCOLYSIS
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
KREBS CYCLE
Glucose
Pyruvic acid
Cytoplasmic fluid
Mitochondrion
Figure 6.8

14. 6.14 REVIEW: EACH MOLECULE OF GLUCOSE YIELDS 38 MOLECULES OF ATP
For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules
Cytoplasmic fluid
Mitochondrion
Electron shuttle across membranes
KREBS CYCLE
GLYCOLYSIS
2 Acetyl CoA
2 Pyruvic acid
KREBS CYCLE
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Glucose
by substrate-level phosphorylation
used for shuttling electrons from NADH made in glycolysis
by substrate-level phosphorylation
by chemiosmotic phosphorylation
Maximum per glucose:
Figure 6.14

15. FERMENTATION: An alternative to Cellular Respiration
Occurs when there is NO oxygen. ANAEROBIC
Only glycolysis occurs (not Kreb’s or the ETS).
This is how yeast converts pyruvic acid to alcohol (when making beer and wine).
This also occurs in our muscles when we work out, then lactic acid is produced.
Lactic acid fermentation in bacteria is also used to make cheese and yogurt.