1. Lecture #18 Cellular Respiration
AP Biology
Lecture #18
Cellular Respiration

2. Carbon dioxide, water are required Oxygen is released
1) Water is split by light energy. Oxygen escapes. Coenzymes pick up electrons, H+.
2)  ATP energy drives synthesis
of glucose from hydrogen and electrons, plus carbon and oxygen (from CO2).
Carbon dioxide, water are required
Oxygen is released
Carbon dioxide, water are released
1) Glucose is degraded to CO2 and water. Coenzymes pick up electrons, hydrogen.
2)  Coenzymes give up electrons, hydrogen to oxygen-requiring transfer chains that release energy to drive ATP formation.
Oxygen is required
Figure 7.2 Page 112
ATP is available to drive cellular tasks

3. Linked Processes Photosynthesis Aerobic Respiration Anabolic Pathway
Energy-storing pathway
Releases oxygen
Requires carbon dioxide
Aerobic Respiration
Catabolic Pathway
Energy-releasing pathway
Requires oxygen
Releases carbon dioxide

4. What is Cellular Respiration?
The process of converting food energy into ATP energy
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP

5. Why are both Photosynthesis and Cell Respiration important to Ecosystems?
Light is the ultimate source of energy for all ecosystems
Chemicals cycle and Energy flows
Photosynthesis and cellular respiration are opposite reactions

6. Why do plants need both chloroplasts and mitochondria?
Chloroplasts use energy from the sun to make glucose
Mitochondria convert glucose to ATP—the energy currency of the cell

7. What is ATP? Adenosine Triphosphate Energy currency of the cell
5-Carbon sugar (Ribose)
Nitrogenous base (Adenine)
3 Phosphate groups
Energy currency of the cell
The chemical bonds that link the phosphate groups together are high energy bonds
When a phosphate group is removed to form ADP and P, small packets of energy are released

8. How is ATP used?
As ATP is broken down, it gives off usable energy to power chemical work and gives off some nonusable energy as heat.
Synthesizing molecules for growth and reproduction
Transport work – active transport, endocytosis, and exocytosis
Mechanical work – muscle contraction, cilia and flagella movement, organelle movement

9. Why use ATP energy and not energy from glucose?
Breaking down glucose yields too much energy for cellular reactions and most of the energy would be wasted as heat.
1 Glucose = 686 kcal
1 ATP = 7.3 kcal
1 Glucose → 36 ATP
How efficient are cells at converting glucose into ATP?
38% of the energy from glucose yields ATP, therefore 62% wasted as heat.

10. Cellular Respiration is a Redox Reaction
(Oxidation)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Oxidation is the loss of electrons or H+
Reduction is the gain of electrons or H+
Glucose is oxidized when electrons and H+ are passed to coenzymes NAD+ and FAD before reducing or passing them to oxygen.
Glucose is oxidized by a series of smaller steps so that smaller packets of energy are released to make ATP, rather than one large explosion of energy.
(Reduction)

11. Cell Respiration can be divided into 4 Parts:
1) Glycolysis
2) Oxidation of Pyruvate / Transition Reaction
3) The Krebs Cycle
4) The Electron Transport Chain and
Chemiosmotic Phosphorylation

12. Where do the 4 parts of Cellular Respiration take place?
Glycolysis:
Cytosol
Oxidation of Pyruvate:
Matrix
The Krebs Cycled:
Electron Transport Chain and Cheimiosmotic Phosphorylation:
Cristae

13. Parts of the Mitochondria

14. Anaerobic Respiration (no oxygen required, cytoplasm)
Glycolysis
(substrate level)
Glucose  4 ATP (Net 2 ATP)
2 ATP 2 NADH
2 Pyruvate
Aerobic Respiration (oxygen required, mitochondria)
2. Oxidation of
Pyruvate
2 Pyruvate  2 CO2
2 NADH
2 Acetyl CoA
Krebs Cycle
(substrate level)
2 Acetyl CoA  4 CO2
2 ATP
6 NADH
2 FADH2
Electron
Transport
Chain
(chemiosmotic)
10 NADH  32 ATP
2 FADH2 6 H2O
6 O2
Total: 36 ATP produced

15. ATP is made in two ways:
1) Substrate Level Phosphorylation (glycolysis & Krebs cycle)
2) Chemiosmotic Phosphorylation (electron transport chain)
Substrate-Level Phosphorylation:
Energy and phosphate are transferred to ADP using an enzyme, to form ATP. Phosphate comes from one of the intermediate molecules produced from the breakdown of glucose.

16. Glycolysis Glucose  2 Pyruvate 2 ATP 4 ATP (Net 2 ATP) 2 NADH
Glucose (C6) is split to make
2 Pyruvates (C3)
1st: ATP energy used to phosphorylate glucose (stored energy)
2nd: phosphorylated glucose broken down into two C3 sugar phosphates
3rd: the sugar phosphates are oxidized to yield electrons and H+ ions which are donated to 2 NAD+ → 2 NADH (stored electron and hydrogen for the Electron Transport Chain)
4th: The energy from oxidation is used to make 4 ATP molecules (net 2 ATP)
This is substrate level phosphorylation because an enzyme transfers phosphate to ADP making ATP
Glycolysis produces very little ATP energy, most energy is still stored in Pyruvate molecules.

19. Oxidation of Pyruvate /Transition Reaction
2 Pyruvate  2 CO2
2 NADH
2 Acetyl CoA
When Oxygen is present, 2 Pyruvates go to the matrix where they are converted into 2 Acetyl CoA (C2).
Multienzyme complex:
1st: each Pyruvate releases CO2 to form Acetate.
2nd: Acetate is oxidized and gives electrons and H+ ions to 2 NAD+ → 2 NADH.
3rd Acetate is combined with Coenzyme A to produce 2 Acetyl CoA molecules.
2 NADH’s carry electrons and hydrogens to the Electron Transport Chain.

20. The Krebs Cycle / Citric Acid Cycle
2 Acetyl CoA  4 CO2
2 ATP
6 NADH
2 FADH2
8 Enzymatic Steps in Matrix of Mitochondria: Break down and Oxidize each Acetyl CoA (2-C’s) to release 2 CO2 and yield electrons and H+ ions to NAD+ + 1 FAD → 3 NADH + FADH2. This yields energy to produce ATP by substrate level phosphorylation.
The first step of the Krebs cycle combines Oxaloacetate (4 C’s) with Acetyl CoA to form Citric Acid, then the remaining 7 steps ultimately recycle oxalacetate.
Two Turns of the Krebs Cycle are required to break down both Acetyl Coenzyme A molecules.
The Krebs cycle produces some chemical energy in the form of ATP but most of the chemical energy is in the form of NADH and FADH2 which then go on to the Electron Transport Chain.

23. The Electron Transport Chain
10 NADH  32 ATP
2 FADH2 H2O
Oxygen
NADH and FADH2 produced earlier, go to the Electron Transport Chain.
NADH and FADH2 release electrons to carriers/proteins embedded in the membrane of the cristae. As the electrons are transferred, H+ ions are pumped from the matrix to the intermembrane space up the concentration gradient. Electrons are passed along a series of 9 carriers until they are ultimately donated to an Oxygen molecule.
½ O2 + 2 electrons + 2 H+ (from NADH and FADH2) → H2O.

25. Chemiosmotic Phosphorylation
Hydrogen ions travel down their concentration gradient through a channel protein coupled with an enzyme called ATP Synthase.
As H+ ions move into the matrix, energy is released and used to combine ADP + P → ATP.
Hydrogens are recycled and pumped back across the cristae using the Electron Transport Chain.
ATP diffuses out of the mitochondria through channel proteins to be used by the cell.

26. ATP Synthase Multisubunit complex with 4 parts:
Rotor – spins as H+ ions flow
Stator – holds the rotor and knob complex together in the cristae
Internal Rod – extends between rotor and knob, spins when rotor spins which then turns the knob
Knob – contains 3 catalytic sites that when turned change shape and activate the enzyme used to make ATP

27. Review ATP Production:
1) Glycolysis → 2 ATP
2) Oxidation of Pyruvate → No ATP
3) The Krebs Cycle → 2 ATP
4) The Electron Transport Chain and Chemiosmotic Phosphorylation:
Each NADH produces 2-3 ATP so NADH → 28 ATP
Each FADH2 produces 2 ATP so FADH2 → 4 ATP
Total = 36 ATP
1 Glucose = 686 kcal
1 ATP = 7.3 kcal
1 Glucose → 36 ATP
How efficient are cells at converting glucose into ATP?
38% of the energy from glucose yields ATP, therefore 62% wasted as heat (used to maintain body temperature or is dissipated)
Ex. Most efficient Cars: only 25% of the energy from gasoline is used to move the car, 75% heat.

30. All Types of Molecules can be used to form ATP by Cell Respiration:
Proteins, Carbohydrates, and Lipids must first be broken down into their monomers and absorbed in the small intestine.
Monomers may be further broken down into intermediate molecules before entering different parts of Cell respiration to ultimately form ATP.

32. Anaerobic Respiration: Fermentation
If there is NO oxygen, then cells can make ATP by Fermentation
Without oxygen, Oxidation of Pyruvate and the Electron Transport Chain do not operate.
Glucose → Pyruvate → Lactate
NAD+ Glycolysis 2 NADH Reduction Rxn or
2 ATP Alcohol + CO2
Fermentation yields a net gain of 2 ATP by substrate level phosphorylation for every 1 Glucose. (Inefficient)
Two Forms of Fermentation:
Lactic Acid Fermentation (animals)
Alcohol Fermentation (yeast)