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 Pi

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 Pi

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 present

Fermentation

Ethanol

or

lactate

Acetyl CoA

MITOCHONDRION

O2 present

Cellular respiration

Citric

acid

cycle

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

Citric

acid

cycle

Oxidative

phosphorylation

Glycolysis

Glucose

Pyruvate

Acetyl CoA

Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphate

–

Inhibits

ATP Citrate

Inhibits

Stimulates

AMP

+

–