1. Cellular Respiration
Section 5-3

2. Cellular Respiration Produces ATP
Before you can use the energy you obtain from food, it has to be transferred to ATP.
Glucose’s energy (and other organic compounds) is transferred to ATP through cellular respiration.
Oxygen makes the production of ATP more efficient, but some ATP is produced without oxygen.

3. Aerobic Respiration – metabolic processes that require oxygen
Anaerobic respiration – metabolic processes that do not require oxygen

4. Overview of Cellular Respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
Figure 5-10 p. 104
STAGE 1: Glucose is converted to pyruvate, producing a small amount of ATP and NADH.
STAGE 2: When oxygen is present, pyruvate and NADH are used to make a large amount of ATP (aerobic respiration). Aerobic respiration occurs in the mitochondria in eukaryotic cells and in the cell membrane of prokaryotic cells. When oxygen is not present, pyruvate is converted to either lactate or ethanol and CO2 (anaerobic respiration).

6. STAGE 1: Glycolysis Glycolysis – the breakdown of glucose
The primary fuel for cellular respiration is glucose.
Glucose formed when carbohydrates (starch and sucrose) are broken down.
If too few carbohydrates are available, other molecules such as fats can be broken down to make ATP. (1 gram of fat = 2 grams carbohydrates)

7. STAGE 1: Glycolysis
Glycolysis – glucose is being broken down in the cytoplasm. It is an enzyme-assisted anaerobic process that breaks down one 6-carbon molecule of glucose to two 3-carbon pyruvates.
Pyruvate – the ion of a 3-carbon organic acid called pyruvic acid
As glucose is broken down, some of its hydrogen atoms are transferred to an electron acceptor called NAD+. This forms the electron carrier called NADH.

9. STAGE 1: Glycolysis
For cellular respiration to continue, the electrons carried by NADH are eventually donated to other organic compounds. This recycles NAD+ making it available to accept more electrons.

10. STAGE 1: Glycolysis Summary of Glycolysis Figure 5-11 p. 105
Step 1: Phosphate groups from 2 ATP molecules transferred to a glucose molecule
Step 2: Resulting 6-carbon compound broken down to 2 3-carbon compounds, each with a phosphate group.
Step 3: 2 NADH molecules produced. 1 more phosphate group transferred to each 3-carbon compound.
Step 4: Each 3-carbon compound is converted to a 3-carbon pyruvate. Produces 4 ATP molecules.
Process uses 2 ATP, produces 4 ATP, so… NET GAIN OF 2 ATP.

11. Glycolysis is followed by another set of reactions that use the energy temporarily stored in NADH to make more ATP.

14. STAGE 2: Aerobic Respiration
When oxygen is present, pyruvate produced during glycolysis enters a mitochondrion. Then pyruvate is converted to a 2-carbon compound.
When pyruvate is converted to a 2-carbon compound – 1 CO2, 1 NADH, and 2-carbon acetyl group is produced.
Acetyl group is attached to a molecule called coenzyme A (CoA) – forms acetyl-CoA

16. STAGE 2: Aerobic Respiration – Kreb’s Cycle
Acetyl-CoA enters a series of enzyme-assisted reactions – Kreb’s cycle
Step 1: Acetyl-CoA combines with a 4-carbon compound, forming a 6-carbon compound and releasing coenzyme-A
Step 2: CO2 released from 6-carbon compound, forming 5-carbon compound. Electrons transferred to NAD+, making a molecule of NADH.

17. STAGE 2: Aerobic Respiration – Kreb’s Cycle
Step 3: CO2 released from 5-carbon compound, forming a 4-carbon compound. 1 ATP and 1 NADH made.
Step 4: 4-carbon compund converted to a new 4-carbon compound. Electrons transferred to an electron acceptor FAD, making a molecule of FADH2 (another type of electron carrier).
Step 5: New 4-carbon compound then converted to the 4-carbon compound that began cycle. Another NADH is produced.

18. STAGE 2: Aerobic Respiration – Kreb’s Cycle
NADH and FADH2 now contain much of the energy that was previously stored in glucose and pyruvate.
Recycles the 4-carbon compound.

21. STAGE 2: Aerobic Respiration – Electron Transport Chain
The electrons donated by NADH and FADH2 pass through an electron transport chain.
Figure 5-13 p. 107
Occurs in the inner membranes of mitochondria
Energy of the electrons used to pump H+ out of inner mitochondrial compartments
H+ accumulates in outer compartment – produces a concentration gradient across the inner membrane

22. STAGE 2: Aerobic Respiration – Electron Transport Chain
H+ diffuses back into inner compartment through a carrier protein that adds a phosphate group to ADP to make ATP.
At end of electron transport chain, H+ and spent electrons combine with O2 to form H2O – oxygen is final electron acceptor.

25. Fermentation
Fermentation follows glycolysis in the absence of oxygen. – anaerobic respiration
When enough oxygen is not present for aerobic respiration to occur, electron transport chain does not function. Why? Oxygen is not able to serve as final electron acceptor. Also, NADH electrons not transferred, so NAD+ cannot be recycled.

26. Fermentation
Anaerobic Respiration – NAD+ recycled in a different way. Electrons carried by NADH are transferred to pyruvate that is produced in glycolysis. This recycles NAD+ so it can continue making ATP through glycolysis.
Fermentation – recycling NAD+ using an organic hydrogen acceptor

27. Lactic Acid Fermentation
3-carbon pyruvate converted to a 3-carbon lactate. NAD+ recycled.
Lactate – ion of organic acid called lactic acid
During vigorous exercise, pyruvate in muscles converted to lactate when muscles operate without enough oxygen.
Causes soreness because it builds up in muscles – blood does not remove it fast enough

29. Alcoholic Fermentation
3-carbon pyruvate converted to a 2-carbon ethanol molcule. CO2 is released.
2 Step Process:
1. Pyruvate converted to a 2-carbon
compound – CO2 released.
2. Electrons transferred from NADH to
the 2-carbon compound producing ethanol.
NAD+ recycled
Yeast or fungi – foods and beverages (wine, beer, rising of bread dough)

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