1. Cellular Respiration Part 5 Fermentation – Pages

2. Fermentation is an anaerobic alternative to cellular respiration Most cellular respiration requires O 2 to produce ATP Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) In the absence of O 2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

3. Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD +, which can be reused by glycolysis Two common types are alcohol fermentation and lactic acid fermentation

4. Fig. 9-18a 2 ADP + 2 P i 2 ATP GlucoseGlycolysis 2 Pyruvatek 2 NADH 2 NAD + + 2 H + CO 2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2

5. Alcoholic Fermentation In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO 2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking

6. Fig. 9-18b Glucose 2 ADP + 2 P i 2 ATP Glycolysis 2 NAD + 2 NADH + 2 H + 2 Pyruvate 2 Lactate (b) Lactic acid fermentation

7. Lactic Acid Fermentation In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO 2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O 2 is scarce

8. Lactic Acid vs. Alcoholic Both ▫Recycle NAD+ to allow glycolysis to continue ▫Anaerobic Lactic Acid ▫Animals and bacteria ▫Produces lactate Alcoholic ▫Yeast and some plants ▫Produces alcohol and CO2

9. Anaerobic vs Aerobic Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O 2 in cellular respiration Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

10. Obligate Anaerobe vs. Facultative Anaerobe Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

11. Fig. 9-19 Glucose Glycolysis Pyruvate CYTOSOL No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle

12. Cells can use many different organic molecules for energy… We can obtain energy from various organic molecules Glycolysis works with many different carbohydrates Proteins must be digested to amino acids then they can enter cellular respiration Fats can be broken down into glycerol and fatty acids to enter cellular respiration

13. Fig. 9-20 Proteins Carbohydrates Amino acids Sugars Fats GlycerolFatty acids Glycolysis Glucose Glyceraldehyde-3- Pyruvate P NH 3 Acetyl CoA Citric acid cycle Oxidative phosphorylation

14. Food molecules provide raw materials for biosynthesis… Excess reactants can be used to build proteins, fats, or carbohydrates

15. Regulation of Cellular Respiration via Feedback Mechanisms Feedback inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. Fig. 9-21 Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits AMP Stimulates Inhibits Pyruvate Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylatio n ATP + – –