NOTES: Ch 9, part 4 -9.5 & 9.6 - Fermentation &

Regulation of Cellular Respiration

9.5 - Fermentation enables some cells to produce ATP without the use of oxygen

● Cellular respiration requires O2 to produce ATP

● Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)

● In the absence of O2, glycolysis couples with fermentation to produce ATP

Alternative Metabolic

Pathways - Vocabulary:

● aerobic: existing in presence of oxygen

 

● anaerobic: existing in absence of oxygen

● FERMENTATION = anaerobic catabolism of organic nutrients

Types of 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

Alcohol Fermentation

Pyruvate + NADH ethanol + CO2 + NAD+

● pyruvate is converted to ethanol

● NADH is oxidized to NAD+ (recycled)

● performed by yeast and some bacteria

● In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2

● Alcohol fermentation by yeast is used in brewing, winemaking, and baking

Alcohol Fermentation

CO2

+ 2 H+

2 NADH2 NAD+

2 Acetaldehyde

2 ATP2 ADP + 2 P i

2 Pyruvate

2

2 Ethanol

Alcohol fermentation

Glucose Glycolysis

Lactic Acid Fermentation

Pyruvate + NADH lactic acid + NAD+

● pyruvate is reduced to lactic acid (3-C

compound); no CO2 produced

● NADH is oxidized to NAD+ (recycling of

NAD+)

● 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 O2 is scarce

Lactic Acid Fermentation

+ 2 H+

2 NADH2 NAD+

2 ATP2 ADP + 2 P i

2 Pyruvate

2 Lactate

Lactic acid fermentation

Glucose Glycolysis

Fermentation and Cellular Respiration Compared:

● Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate

● in fermentation, NADH is recycled back to

NAD+

● in fermentation, final electron acceptor is

pyruvate, not O2

Fermentation and Cellular Respiration Compared:

● amount of energy harvested:

Fermentation = 2 ATP

Cellular respiration = 36-38 ATP

● oxygen NOT required for fermentation

● Obligate anaerobes: only grow in absence of oxygen (e.g. clostridium botulinum)

 

● Obligate aerobes: only grow in presence of oxygen

Micrococcus luteus

● Facultative anaerobes: can grow in either presence or absence of oxygen (e.g. yeast or bacteria that make yogurt, cheese; our muscle cells at the cellular level)

 

*in a faculatative anaerobe, pyruvate is a “fork” in the metabolic road which leads to 2 alternate catabolic routes:

-if O2 is present: Krebs and E.T.C.

-if no O2 is present: Fermentation

Pyruvate

Glucose

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 present Cellular respiration

Citricacidcycle

The Evolutionary Significance of Glycolysis

● Glycolysis occurs in nearly all organisms

● Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

9.6 - Glycolysis and the Krebs cycle connect to many other metabolic pathways

● Gycolysis and the Krebs cycle are major intersections to various catabolic and anabolic pathways

The Versatility of Catabolism● Catabolic pathways funnel electrons from many

kinds of organic molecules into cellular respiration● Glycolysis accepts a wide range of carbohydrates● Proteins must be digested to amino acids; amino

groups can feed glycolysis or the Krebs cycle● Fats are digested to glycerol (used in glycolysis)

and fatty acids (used in generating acetyl CoA) ● An oxidized gram of fat produces more than twice

as much ATP as an oxidized gram of carbohydrate

Citricacidcycle

Oxidativephosphorylation

Proteins

NH3

Aminoacids

Sugars

Carbohydrates

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

Fattyacids

Glycerol

Fats

Biosynthesis (Anabolic Pathways)

● The body uses small molecules to build other substances

● These small molecules may come directly from food, from glycolysis, or from the Krebs cycle

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

Citricacidcycle

Oxidativephosphorylation

Glycolysis

Glucose

Pyruvate

Acetyl CoA

Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphate

–

Inhibits

ATP Citrate

Inhibits

Stimulates

AMP

+

–