Cellular Respiration, Harvesting Chemical Energy Fermentation ...

Chapter 9 – Cellular Respiration, Harvesting Chemical Energy
Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration requires O 2
to produce ATP
Glycolysis CitricOxidative
acid phosphorylation:
cycle electron transport
ATP and ATPchemiosmosis
H +
Protein complex
Intermembrane
of electron
space carriers
Inner
mitochondrial
membrane
Mitochondrial
matrix
I
H +
Q
III
II
FADH 2FAD
Cyt c
Inner
mitochondrial
membrane
NADH+ H + NAD +
ADP + P
(carrying electrons
i ATP
from food)
H +
Electron transport chain
Chemiosmosis
Electron transport and pumping of protons ATP (H + ), synthesis powered by the flow
Which create an H + gradient Oxidative across phosphorylation
the membrane of H + back across the membrane
IV
2H + + 1 /2 O 2
H +
H 2 O
H +
ATP
synthase
•Glycolysis can produce ATP with or without
O 2
(in aerobic or anaerobic conditions)
pyruvate
•Two common types are
2 ATP
2 ADP + 2 P i
2 Pyruvate
Glucose
Glycolysis
Alcohol Fermentation
2
CO 2
•In alcohol fermentation, pyruvate is converted to
ethanol in two steps, with the first releasing CO 2
2 Ethanol
Alcohol fermentation
2 NAD + 2 NADH
+ 2 H +
2 Acetaldehyde
•This reaction regenerates NAD+ needed for the continuation of glycolysis.

Lactic Acid Fermentation
In lactic acid fermentation,
Glucose
2 ATP
Glycolysis
2 NAD +
2 NADH
+ 2 H +
2
CO 2
2 ADP + 2 P i
2 Pyruvate
2 Lactate
Lactic acid fermentation
•Lactic acid fermentation by some
fungi and bacteria is used to
make cheese and yogurt
Lactic Acid Fermentation in Human Muscle Cells
•Human muscle cells use lactic acid fermentation to generate ATP when O 2
is scarce
When you walk to class, ATP powers muscles cells of your legs.
Cellular respiration regenerates ATP supply to keep you going.
If you start to run to class,
In order to keep running, your muscles must generate ATP by the anaerobic process of fermentation.
NAD+ must also be present as an electron acceptor for glycolysis to occur.
2 pyruvate

Lactic Acid Fermentation in Human Muscle Cells
NAD+ is present under aerobic condition of cellular respiration.
NAD+ is regenerated by the cell
NAD+ cannot be recycled by the cell under anaerobic conditions,
2 pyruvate
This addition of electrons produces the waste product, lactic acid.
Glucose
2 NAD + 2 NADH
2
+ 2 H +
2 Pyruvate
CO 2
2 ADP + 2 P i 2 ATP
Glycolysis
2 Lactate
Lactic acid fermentation
Fermentation and Cellular Respiration Compared
•Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
2 ADP + 2 P i
2 Pyruvate
pyruvate
Glucose
2 ATP
Glycolysis
2 NAD +
2 NADH
+ 2 H +
2
CO 2
2 Lactate
Lactic acid fermentation

Fermentation and Cellular Respiration Compared
The processes have different final electron acceptors:
2 ADP + 2 P i
2 Pyruvate
Glucose
2 ATP
Glycolysis
2 NAD +
2 NADH
+ 2 H +
2
CO 2
Glucose
2 ADP + 2 P i 2 ATP
Glycolysis
2 Pyruvate
2 NAD + 2 Acetaldehyde
2 NADH
+ 2 H +
2
CO 2
2 Lactate
Lactic acid fermentation
2 Ethanol
Alcohol fermentation
The processes have different final electron acceptors:
Inner
mitochondrial
Glycolysis Citric Oxidative
membrane
acid phosphorylation:
cycle electron transport
ATP ATP and chemiosmosis ATP
H +
H +
H +
H
Protein complex
Cyt c
+
Intermembrane
of electron
space
carriers
Q
IV
I
III
ATP
Inner
II
FADH 2H + + 1 /2 O
mitochondrial
2 FAD
2 H 2 O
synthase
membrane
NADH+ H + NAD +
(carrying electrons
ADP + P i ATP
from food)
H +
Mitochondrial
Electron transport chain
Chemiosmosis
matrix
Electron transport and pumping of protons (H + ), ATP synthesis powered by the flow
Which create an H + gradient
Oxidative
across the
phosphorylation
membraneof H + back across the membrane
•Cellular respiration produces much more ATP
Some organisms can carry out only fermentation (anaerobic respiration).
Yeast and many bacteria are facultative anaerobes,
Glucose
In a facultative anaerobe,
CYTOSOL
Pyruvate
No O 2 present
Fermentation
O 2 present
Cellular respiration
Ethanol
or
lactate
Acetyl CoA
MITOCHONDRION
Citric
acid
cycle

The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms
Membrane-bound organelles
Accumulation of atmospheric
oxygen from photosynthetic
cyanobacteria
Oldest prokaryotic fossils
Earth cool enough for crust to solidify
Origin of Earth
Glycolysis and the citric acid cycle connect to many other metabolic pathways
•Gycolysis and the citric acid 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
Proteins
Carbohydrates
Fats
Proteins must be digested to amino acids;
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH 3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation

Regulation of Cellular Respiration via Feedback Mechanisms
•Feedback inhibition is the most common mechanism for
control of glycolysis and the Krebs Cycle.
If ATP concentration begins to drop, respiration speeds up;
when there is plenty of ATP, respiration slows down
Glucose
–
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
AMP
Stimulates
+
–
Inhibits
Fructose-1,6-bisphosphate
Inhibits
Phosphofructokinase is an
allosteric enzyme with receptor
sites for specific inhibitors
and activators.
Fructose-6-phosphate
ATP
Phosphofructokinase
Pyruvate
ADP
ATP
Acetyl CoA
Citrate
Fructose-
1, 6-bisphosphate
Citric
acid
cycle
Allosteric Regulation of Enzymes
Oxidative
phosphorylation
Allosteric regulation is the term used to describe cases where a
Allosteric regulation may either inhibit or stimulate an enzyme’s activity
Allosteric enzyme
with four subunits
Active site
(one of four)
Allosteric activator
stabilizes active form.
Most allosterically regulated enzymes are made from polypeptide subunits
Regulatory
site (one
of four)
Active form
Activator
Stabilized active form
Oscillation
Allosteric inhibitor
stabilizes inactive form.
Nonfunctional
active site
Inactive form Inhibitor Stabilized inactive
form
Allosteric activators and inhibitors

Regulation of Cellular Respiration via Feedback Mechanisms
–
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
AMP
Stimulates
+
–
Inhibits
Fructose-1,6-bisphosphate
Inhibits
Phosphofructokinase is also sensitive to citrate production
in the Krebs Cycle.
Pyruvate
If citrate accumulates in the mitochondria,
ATP
Acetyl CoA
Citrate
Citric
acid
cycle
Oxidative
phosphorylation
Study outline-Chapter 9-Cellular Respiration
-Understand the two common types of fermentation (Fig. 9.18)
-alcohol fermentation
-lactic acid fermentation
-What types of processes use alcohol fermentation?
-Understand how fermentation works in human muscle cells.
-Know terms-anaerobic, fermentation
-What metabolic pathway provides ATP during fermentation?
-Why can’t NAD+ be recycled by the cell under anaerobic conditions?
-What waste product that is produced in the fermentation process in muscle cells?
-What waste products are produced in the fermentation of yeast?
-Understand similarities and differences between fermentation and cellular respiration
-Know terms-obligate anaerobes
-facultative anaerobes (Fig. 9.19)
-Understand the evolutionary significance of glycolysis
-Understand how glycolysis and the citric acid cycle connect to other metabolic pathways (Fig. 9.20)
-Understand the regulation of cellular respiration via feedback mechanisms (Fig. 9.21)
-Know terms-allosteric enzymes