1. Objectives
Contrast the roles of glycolysis and aerobic respiration in cellular respiration.
Relate aerobic respiration to the structure of a mitochondrion.
Summarize the events of the Krebs cycle.
Summarize the events of the electron transport chain and H+/ ATP synthase pump.
Calculate the efficiency of aerobic respiration.

2. Photosynthesis Cell Respiration Cycle
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
Organic molecules
+ O2
ATP
powers most cellular work
Heat energy

3. Life Is Work Living cells
Require transfusions of energy (a.k.a., food) from outside sources to perform their many tasks
The giant panda obtains energy for its cells by eating plants

4. Harvesting Chemical Energy
Cellular respiration is the process by which cells break down organic compounds to produce ATP.
Both autotrophs and heterotrophs use cellular respiration to make CO2 and water from organic compounds and O2.
The products of cellular respiration are the reactants in photosynthesis; conversely, the products of photosynthesis are reactants in cellular respiration.
Cellular respiration can be divided into two stages: glycolysis and aerobic respiration.

5. Oxidative phosphorylation: electron transport and chemiosmosis
An overview of cellular respiration…
Electrons
carried
via NADH
Glycolsis
Glucose
Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Citric acid cycle
Oxidative phosphorylation: electron transport and chemiosmosis
Oxidative
Mitochondrion
Cytosol
AEROBIC RESPIRATION

6. Cellular Respiration

7. CELLULAR RESPIRATION (Figure 5.4, p. 133)
ALL organisms do respiration!!!
energy in glucose released to produce ATP
two types of respiration
AEROBIC (requires oxygen)
ANAEROBIC (does not require oxygen)
both types start with glycolysis

8. GLYCOLYSIS (Figure 5.6, p. 135)
glycolysis is the first step of respiration
occurs in ALL cells!!!
occurs in cytoplasm and is anaerobic (no O2)
glucose is converted to pyruvic acid
produces 2 ATP (~2% of energy in 1 glucose)
pyruvic acid then used in…
fermentation or
aerobic respiration

9. Summary of Cellular Respiration

10. FERMENTATION (ANAEROBIC)
occurs in cytoplasm
consumes pyruvic acid with no ATP production!!!
LACTIC ACID FERMENTATION – creates lactic acid
example overworked muscles with low O2
feels like cramp or soreness
ALCOHOLIC FERMENTATION - produces ethyl alcohol and CO2
used to make beer; wine; dough

11. (a) Alcohol fermentation (b) Lactic acid fermentation
In alcohol fermentation
Pyruvate is converted to ethanol in two steps, one of which releases CO2
During lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate as a waste product
2 ADP + 2 P1
2 ATP
Glycolysis
Glucose
2 NAD+
2 NADH
2 Pyruvate
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 Lactate
(b) Lactic acid fermentation H OH
CH3 C
O – O O–
CO2 2

12. Overview of Aerobic Respiration
In eukaryotic cells, the processes of aerobic respiration occur in the mitochondria. Aerobic respiration only occurs if oxygen is present in the cell.
The Krebs cycle occurs in the mitochondrial matrix. The electron transport chain (which is associated with the production of ATPs) is located in the inner membrane.

13. Mitochondria, the super-energy harvesters
are the sites of aerobic cellular respiration
are found in nearly all eukaryotic cells
are enclosed by two membranes
smooth outer membrane
an inner membrane folded into cristae (i.e., higher surface area for chemical reactions)

14. Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Mitochondrial
DNA
Inner
Cristae
Matrix
100 µm

15. AEROBIC RESPIRATION (requires O2)
Net reaction…
mitochondria
C6H12O6 + 6O  CO2 + 6H2O + ATP
enzymes

16. The Krebs Cycle
In the mitochondrial matrix, pyruvic acid produced in glycolysis reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle.
One glucose molecule is completely broken down in two turns of the Krebs cycle. These two turns produce four CO2 molecules, two ATP molecules, and hydrogen atoms* that are used to make six NADH* and two FADH2* molecules.
* The energy released by the breakdown of glucose is about to be transferred to ATP!!!

17. Summary of Cellular Respiration

18. AEROBIC RESPIRATION (requires O2)
occurs ONLY in mitochondria (Figure 5.10, p.138)
pyruvic acid from glycolysis is metabolized in the KREB’S CYCLE
occurs in the matrix
two turns of cycle (1 glucose molecule) yields 4 CO2, 2 ATP, and several energy rich molecules (NADH and FADH2 )
the energy rich molecules NADH and FADH2 are used to make a lot of ATP energy rich (using electron transport chains and ATP synthase)

19. KREB’S CYCLE (in the matrix)

20. Enzymes in the Kreb’s (or citric acid) cycle…
pyruvate

21. Summary of Kreb’s (Citric Acid) Cycle
X 2
diffuse out
X 2
used in e- transport chain
X 2
X 2
used in e- transport chain
X 2

22. Electron Transport Chain and ATP Synthesis
High-energy electrons from from NADH and FADH2 are passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane.
Hydrogen ions, H+, are also given up by NADH and FADH2.
As the electrons move through the electron transport chain, they lose energy. This energy is used to pump protons from the matrix into the intermembrane space.
The resulting concentration gradient of hydrogen ions drives ATP synthase and ATP production!

23. Electron Transport Chain, H+, & ATP synthesis
H+ move through ATP synthase to make ATP from ADP+Pi
Oxygen combines with the electrons and protons to form water.

24. Electron Transport Chain and ATP synthase
The Importance of Oxygen
ATP can be synthesized using the diffusion of H+ ions from the outer compartment to the inner compartment only if electrons continue to move along the electron transport chain.
Oxygen is the final electron acceptor
As a result, ATP can continue to be made through the ATP pump.

25. ATP Synthase
makes ATP !!!

26. An Accounting of ATP Production by Cellular Respiration
During respiration, most energy flows in this sequence
glucose î NADH î e- transport chain î H+ gradient î ATP

27. Energy Summary of Cellular Respiration

28. AEROBIC RESPIRATION Electron Transport Chains & ATP synthesis
uses membrane bound proteins
O2 molecules are consumed
this produces 32 more ATP
SO... total yield of ATP (1 glucose molecule) from aerobic respiration AND glycolysis = 38 ATP
19-times more ATP than from anaerobic respiration alone !!! (~40% of the energy in a glucose molecule is converted to ATP)
WHAT HAPPENS TO THE OTHER 60%?

29. Summary of Cellular Respiration

30. Another Role of Cellular Respiration
A Summary of Cellular Respiration
Another Role of Cellular Respiration
Providing cells with ATP is not the only important function of cellular respiration.
Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.
fatty acids, glycerol, amino acids

31. Comparing Aerobic and Anaerobic Respiration

32. Fermentation consists of
(REVIEW) Glycolysis
Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
Glycolysis is often coupled with fermentation to produce a few more ATP, especially in prokaryotes
Fermentation consists of
Glycolysis plus either alcohol or lactic acid fermentation

33. Fermentation and Cellular Respiration Compared
Both fermentation and cellular respiration
Use glycolysis to oxidize glucose and other organic fuels to pyruvate
Cellular respiration (i.e., complete oxidation) is more efficient than anaerobic respiration pathways
Produces more 19x more ATP (38 versus 2 ATP)

34. Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
Ethanol or
lactate
Acetyl CoA
MITOCHONDRION
Citric
acid
cycle

35. The Evolutionary Significance of Glycolysis
Occurs in nearly all organisms
Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere
The pathways are similar (or conserved) across nearly all kingdoms (i.e., they are physiologically important and have not changed very much)