LECTURE 6
: CELLULAR RESPIRATIONI. Energy Processes in Cells.
A. Major processes are cellular respiration and photosynthesis.
B. Photosynthesis: sunlight energy converted to glucose.
C. Cellular respiration: glucose broken down to produce ATP.
II. Aerobic Respiration: General Comments.
A. Major pathway of cellular respiration.
B. Overview of aerobic respiration.
1. Takes place in the mitochondria of eukaryotic cells.
2. Occurs when O2 s available to the cell.
3. Simple equation:
C. Oxidation-reduction reaction (redox reaction).
1. Oxidation: loss of electrons and hydrogen atoms by a molecule — e.g. glucose.
2. Reduction: gain of electrons and hydrogen atoms by a molecule — e.g. water.
D. Bonds holding glucose together are broken in a stepwise fashion.
E. Phosphorylation — energy used to convert ADP to ATP.
F. 1 molecule of glucose can produce 38 molecules of ATP via aerobic respiration.
III. Aerobic Respiration: The Specifics.
A. 3 separate processes: glycolysis, the Krebs cycle, and oxidative phosphorylation. (Figure 6.7).
B. Glycolysis -- "splitting of sugar."
1. 1 glucose molecule (C6) split into 2 molecules of pyruvic acid (C3).
2. Occurs in the cytosol of the cell.
3. 2 ATP are generated directly.
4. NAD+ picks up hydrogens and electrons to become NADH.
5. Figure 6.8.
C. The Krebs Cycle.
1. Each pyruvic acid molecule enters a cyclic series of reactions.
2. All 6 original carbon atoms in the glucose molecule are converted into CO2.
3. 2 more ATPs are generated (1 per pyruvic acid).
4. More NADHs and some FADH2s (another hydrogen acceptor) are produced.
5. Figure 6.11
D. Oxidative phosphorylation-- where the "ATP action" is in the cell.
1. Occurs in electron transport system in the mitochondria.
2. Electron transport system composed of cytochromes.
3. Phosphorylation of ADP using electrons and hydrogen atoms (NADHs).
4. 34 ATPs generated.
5. Hydrogens and electrons combined with O2 to form H2O ("metabolic water").
E. How electron transport works.
1. Electrons carried by NADH and FADH2 have lots of energy.
2. Electrons release energy as they move down ETC.
3. Energy released is used to phosphorylate ADP to ATP.
4. Electrons and the hydrogens they came from combine with O2 to form H2O.
5. Figure 6.6.
F. An overview of ATP production in aerobic respiration. (Figure 6.14)
G. Some miscellaneous points about aerobic respiration.
1. O2 must be present to accept H+ and electrons.
2. Cytochromes have high affinities for other molecules — e.g. CO, cyanide.
3. Some organisms can use "metabolic water" to meet all their water balance needs.
4. Prokaryotes (e.g. bacteria) can’t do aerobic respiration.
5. ATP generated by respiration used to meet the energy demands of the cell.
6. Plants photosynthesize AND respire.
H. The link between cellular and organismal respiration.
I. How other foods are handled.
1. Polysaccharides.
2. Fats.
3. Proteins.
4. Figure 6.13.
IV. Anaerobic Respiration.
A. Respiration in the absence of oxygen.
B. Efficiency rate of only 2.1% compared to aerobic respiration.
C. Anaerobic respiration is a means of continuing glycolysis.
D. Organisms do 2 different types of anaerobic respiration.
1. Alcohol fermentation -- yeast and plants.
2. Lactic acid fermentation — prokaryotes and animals.
C. Both types begin with glycolysis.
1. 2 ATP's produced and 2 NAD+ converted to 2 NADH.
2. Next step is to convert NADH back to NAD+ so glycolysis can continue.
D. Alcohol fermentation.
1. 2 pyruvic acids (2C3) converted to 2 molecules of ethanol (ethyl alcohol) (2C2).
2. 2 carbon dioxides (2CO2) are released.
3. 2 NADH are oxidized to 2 NAD+ that are then used in glycolysis.
4. Figure 6.15.
E. Lactic acid fermentation.
1. 2 pyruvic acid molecules (2C3) converted to 2 lactic acid molecules (2C3).
2. 2 ATPs produced.
3. 2 NADH are oxidized to 2 NAD+ that are then used in glycolysis.
4. Figure 6.15.
F. A few miscellaneous comments about anaerobic respiration.
1. Only 2 ATP's produced per glucose (compare that with aerobic respiration!).
2. Alcohol fermentation is commercially important.
3. Lactobacillus and sour milk.
4. Strenuous exercise: "feel the burn!"
5. Marathoners and sprinters.
6. "Getting in shape."
NEXT TIME: Photosynthesis (Chapter 7)