NOTES: Ch 9, part 4 - 9.5 & 9.6 - Fermentation & Regulation of Cellular Respiration.
Transcript of NOTES: Ch 9, part 4 - 9.5 & 9.6 - Fermentation & Regulation of Cellular Respiration.
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
+
–