Cellular Respiration Part 5 Fermentation Pages Fermentation is

Cellular Respiration Part 5 Fermentation – Pages

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

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

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

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

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

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

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 CO 2

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

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

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

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

Fig. 9 -20 Proteins Amino acids Fats Carbohydrates Sugars Glycerol Glycolysis Glucose Glyceraldehyde-3 -P NH 3 Pyruvate Acetyl Co. A Citric acid cycle Oxidative phosphorylation Fatty acids

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

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

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