1. Cellular Respiration: Harvesting Chemical Energy
Chapter 8
Cellular Respiration:
Harvesting Chemical Energy

2. Aerobic & Anaerobic Metabolism
Aerobic metabolism - When enough oxygen reaches cells to support energy needs
- Maximum energy production
Anaerobic metabolism
When the demand for oxygen outstrips the body’s ability to deliver it
Low energy production

3. AEROBIC HARVEST OF FOOD ENERGY
Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP for cellular work
Cellular respiration is an aerobic process requiring oxygen

4. The Versatility of Cellular Respiration
Cellular respiration can “burn” other kinds of molecules besides glucose:
Diverse types of carbohydrates
Fats
Proteins 4 4

5. The Overall Equation for Cellular Respiration
A common fuel molecule for cellular respiration is glucose
This is the overall equation for what happens to glucose during cellular respiration
Glucose
Oxygen
Carbon dioxide
Water
Energy

6. But Remember …
Cellular Respiration is a metabolic pathway, not a single reaction
Many chemical reactions, both aerobic and anaerobic, are involved in the process of cellular respiration
Lots of enzymes are required for the process to occur

7. The Relationship Between Cellular Respiration and Breathing
Cellular respiration and breathing are closely related
Cellular respiration requires a cell to exchange gases with its surroundings
Breathing exchanges these gases between the blood and outside air

8. The Role of Oxygen in Cellular Respiration
During cellular respiration, hydrogen and its bonding electrons change partners
Hydrogen and its electrons go from sugar to oxygen, forming water

9. Comparison Respiration Photosynthesis Occurs in all organisms
Occurs in only chlorophyll containing organisms
Breaks down glucose
Stores light energy as chemical energy in the bonds of glucose
Releases carbon dioxide, water, & ATP
Produces glucose and oxygen
Exergonic Reaction
Endergonic reaction

10. The Metabolic Pathway of Cellular Respiration
All of the reactions involved in cellular respiration can be grouped into three main stages
Glycolysis – occurs in cytoplasm
The Krebs cycle – occurs in matrix of mitochondria
Electron transport – occurs across the mitochondrial membrane

11. A Road Map for Cellular Respiration
Mitochondrion
Cytosol
High-energy
electrons
carried
by NADH
High-energy
electrons carried
mainly by
NADH
Glycolysis
Krebs
Cycle 2
Pyruvic
acid
Electron
Transport
Glucose

12. Glycolysis
Stage One

13. Stage 1: Glycolysis Glycolysis takes place in the cytoplasm
Oxygen NOT required
Process breaks a six-carbon glucose into two, three-carbon molecules
A molecule of glucose is split into two molecules of pyruvic acid
These molecules then donate high energy electrons to NAD+, forming NADH

14. Glycolysis
METABOLIC PATHWAY
2 Pyruvic acid
Glucose

15. Glycolysis CoA Acetic acid Pyruvic Acetyl-CoA acid (acetyl-coenzyme A)15 15

16. Krebs Cycle
Stage Two

17. Stage 2: The Krebs Cycle
The Krebs cycle completes the breakdown of sugar
It occurs inside the mitochondria
In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form by combining it with enzyme Co-A to make Acetyl-CoA

18. ACETYL Co-A ADP Krebs Cycle Input Output Acetic acid 2 CO2 3 NAD FAD1
Acetic acid
2 CO2 3
ADP
Krebs
Cycle
3 NAD 4
FAD 5 6

19. Electron Transport
Stage 3

20. Stage 3: Electron Transport
Electron transport releases the energy your cells need to make the most of their ATP
The molecules of electron transport chains are built into the inner membranes of mitochondria

21. Stage 3: Electron Transport
The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane
These ions store potential energy

22. Electron transport chain
Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen
Chemiosmosis: energy coupling mechanism
ATP synthase: produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)

23. Electron transport chain
Protein
complex
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Electron transport chain
ATP synthase

24. Food
Polysaccharides
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
Acetyl-
CoA
Krebs
Cycle
Glycolysis
Electron
Transport

25. Adding Up the ATP Cytosol Mitochondrion Glycolysis 2 Acetyl- CoA 2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Glucose
Maximum
per
glucose: by
direct
synthesis by
ATP
synthase
by direct
synthesis
Figure 6.14

26. FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY
Some of your cells can actually work for short periods without oxygen (anaerobic respiration)
For example, muscle cells can produce ATP under anaerobic conditions
Called Fermentation
Involves The anaerobic harvest of food energy

27. Fermentation in Human Muscle Cells
Human muscle cells can make ATP with and without oxygen
They have enough ATP to support activities such as quick sprinting for about 5 seconds
A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds
To keep running, your muscles must generate ATP by the anaerobic process of fermentation

28. Glycolysis is the metabolic pathway that provides ATP during fermentation
Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going
In human muscle cells, lactic acid is a by-product

29. Lactic acid fermentation
2 ADP+ 2
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Lactic
acid
Lactic acid fermentation

30. Fermentation in Microorganisms
Various types of microorganisms perform fermentation
Yeast cells carry out a slightly different type of fermentation pathway
This pathway produces CO2 and ethyl alcohol

31. Alcoholic fermentation
2 ADP+ 2
2 CO2 released
2 ATP
Glycolysis
2 NAD
2 NAD
Glucose
2 Ethyl
alcohol
2 Pyruvic
acid
+ 2 H
Alcoholic fermentation

32. The food industry uses yeast to produce various food products

33. Related metabolic processes
Fermentation: alcohol~ pyruvate to ethanol lactic acid~ pyruvate to lactate
Facultative anaerobes (yeast/bacteria)

34. Review: Cellular Respiration
Glycolysis:
2 ATP (substrate-level phosphorylation)
Kreb’s Cycle:
Electron transport & oxidative phosphorylation:
2 NADH (glycolysis) = 6ATP
2 NADH (acetyl CoA) = 6ATP
6 NADH (Kreb’s) = 18 ATP
2 FADH2 (Kreb’s) = 4 ATP
38 TOTAL ATP/glucose

36. Sunlight supplies the energy!
Bonds of Glucose, made in chloroplasts, contain the stored energy
Ecosystem
Photosynthesis
(in chloroplasts)
Raw materials for cellular respiration
Glucose
Carbon dioxide
Raw materials for photosynthesis
Oxygen
Water
Glucose broken down to release energy for cellular work
Cellular respiration
(in mitochondria)
Cellular energy
Heat energy 36 36