Download Chapter 9 / Energy-Releasing Pathways and Biosynthesis I

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Chapter 9 / Energy-Releasing Pathways and Biosynthesis
I. Introduction to Energy and Life
A. Living cells require transfusions of energy from outside sources to perform their many
tasks
B. Energy flows into an ecosystem as sunlight and leaves as heat
II. Catabolic Pathways and Production of ATP
A. Catabolic pathways yield energy by oxidizing organic fuels
B. The breakdown of organic molecules is exergonic
C. Fermentation
D. Cellular respiration
III. Redox Reactions: Oxidation and Reduction
A.
B.
C.
D.
Catabolic pathways yield energy due to the transfer of electrons
Redox reactions transfer electrons from one reactant to another by oxidation and reduction
Some redox reactions do not completely exchange electrons
During cellular respiration glucose is oxidized and oxygen is reduced
IV. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
A. Cellular respiration oxidizes glucose in a series of steps
B. Electrons from organic compounds
C. NADH, the reduced form of NAD+
D. If electron transfer is not stepwise…
E. The electron transport chain
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V. Introduction to Cellular Respiration
A. Breakdown of glucose--redox process
glucose oxidized, oxygen reduced
Summary Reaction:
C6H12O6 + 6O2 + 6 H2O → 6CO2 + 12 H2O + 36 or 38 ATPs
B. Consists of three main stages:
glycolysis, citric acid cycle, oxidative phosphorylation (electron transport chain and
chemiosmosis)
VI. The Stages of Cellular Respiration
A. Glycolysis
occurs in cytosol
oxygen not used in this stage
glucose → 2 pyruvate
net gain of 2 ATP
2 major phases:
1) phosphorylation of glucose (energy investment phase)
2) substrate-level phosphorylation (energy payoff phase)
In between first and second stages:
Formation of Acetyl CoA
a. takes place in matrix of mitochondria
b. CO2 removed from pyruvates
c. 2C attached to coenzyme A
d. NAD+ is electron acceptor
B. Citric Acid Cycle
a.k.a. TCA , Krebs cycle
a. takes place in the matrix of mitochondrion
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b. requires oxygen
c. each pyruvate (now converted to acetyl CoA) goes through the cycle
d. 2CO2 produced, 3NAD+ reduced to 3NADH, 1FAD reduced to FADH2
C. Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis)
a. takes place on inner mitochondrial membrane
b. electrons from Hs carried by NADH and FADH2
c. electron transport chain consists of molecules that are electron acceptors and proteins
called cytochromes
d. energy from electrons passing through chain is used to make ATP
e. final electron acceptor is O2; merges with Hs to produce H2O
VII. An Accounting of ATP Production by Cellular Respiration
Net yield of ATPs in aerobic respiration
glycolysis = 2ATP
Krebs cycle = 2ATP
electron transport chain = 32-34 ATP
VIII. Anaerobic Pathways of Respiration
take place in absence of oxygen
not as much ATP produced
A. Anaerobic respiration
inorganic compound (not oxygen) final H acceptor
B. Fermentation
1. alcohol
2. lactic acid
both yield only 2ATPs for 1 molecule of glucose
IX. Fermentation and Cellular Respiration Compared
A. Both use glycolysis to oxidize glucose and other organic fuels to pyruvate
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B.
C.
D.
E.
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Differ in their final electron acceptor
Cellular respiration produces more ATP
Pyruvate is a key juncture in catabolism
Glycolysis occurs in nearly all organisms
X. The Versatility of Catabolism
Use of nutrients other than carbohydrates in aerobic respiration
can catabolize proteins and neutral fats
--enter at different points along pathways
XI. Aspects of Biosynthesis--Anabolism
A. The body uses small molecules to build other substances
B. These small molecules may come directly from food or through glycolysis or the citric acid cycle
continuous with catabolism
synthesizes complex organic molecules
involves enzymes at each step
generally requires energy
not simply reverse of catabolic rxns.
XII. Regulation of Cellular Respiration via Feedback Mechanisms