Download Pathways that Harvest and Store Chemical Energy

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Pathways that Harvest and
Store Chemical Energy
Energy flow and chemical recycling in ecosystems
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
Five principles governing metabolic pathways:
1. Chemical transformations occur in a series of
intermediate reactions that form a metabolic
pathway.
2. Each reaction is catalyzed by a specific
enzyme.
3. Most metabolic pathways are similar in all
organisms.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
4. In eukaryotes, many metabolic pathways
occur inside specific organelles.
5. Each metabolic pathway is controlled by
enzymes that can be inhibited or activated.
Figure 6.1 The Concept of Coupling Reactions
Figure 9.2 A review of how ATP drives cellular work
Figure 6.2 ATP
Substrate-level phosphorylation
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
Energy can also be transferred by the transfer of
electrons in oxidation–reduction, or redox
reactions.
• Reduction is the gain of one or more
electrons.
• Oxidation is the loss of one or more electrons.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
Oxidation and reduction always occur together.
Methane combustion as an energy-yielding redox reaction
NAD+ as an electron shuttle
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
Reduction of NAD+ is highly endergonic:



NAD  H  2e  NADH
Oxidation of NADH is highly exergonic:

NADH  H 
1

2
O2  NAD  H 2O
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play
Important Roles in Biological Energy Metabolism
Oxidative phosphorylation couples oxidation of
NADH:
NADH  NAD  H   2e   energy
with production of ATP:
energy  ADP  Pi  ATP
Figure 6.5 A Chemiosmosis
Figure 6.5 B Chemiosmosis
http://www.stolaf.edu/people/giannini/flas
hanimat/metabolism/atpsyn1.swf
http://www.stolaf.edu/people/giannini/flash
animat/metabolism/atpsyn2.swf
Figure 6.8 Energy Metabolism Occurs in Small Steps
Figure 6.9 Energy-Releasing Metabolic Pathways
An overview of cellular respiration
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen
Releases a Large Amount of Energy
Glycolysis: ten reactions.
Takes place in the cytosol.
Final products:
2 molecules of pyruvate (pyruvic acid)
2 molecules of ATP
2 molecules of NADH
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 1)
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 2)
Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 3)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen
Releases a Large Amount of Energy
Examples of reaction types common in metabolic
pathways:
Step 6: Oxidation–reduction
Step 7: Substrate-level phosphorylation
text art pg 107 here
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen
Releases a Large Amount of Energy
Pyruvate Oxidation:
Products: CO2 and acetate; acetate is then
bound to coenzyme A (CoA)
Figure 6.11 The Citric Acid Cycle
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen
Releases a Large Amount of Energy
Final reaction of citric acid cycle:
Figure 6.12 Electron Transport and ATP Synthesis in Mitochondria
http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20t
ransport.swf
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen
Releases a Large Amount of Energy
About 32 molecules of ATP are produced for
each fully oxidized glucose.
The role of O2: most of the ATP produced is
formed by oxidative phosphorylation, which is
due to the reoxidation of NADH.
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen
Releases a Small Amount of Energy
Under anaerobic conditions, NADH is reoxidized
by fermentation.
There are many different types of fermentation,
but all operate to regenerate NAD+.
The overall yield of ATP is only two—the ATP
made in glycolysis.
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen
Releases a Small Amount of Energy
Lactic acid fermentation:
End product is lactic acid (lactate).
NADH is used to reduce pyruvate to lactic acid,
thus regenerating NAD+.
Figure 6.13 A Fermentation
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen
Releases a Small Amount of Energy
Alcoholic fermentation:
End product is ethyl alcohol (ethanol).
Pyruvate is converted to acetaldehyde, and CO2
is released. NADH is used to reduce
acetaldehyde to ethanol, regenerating NAD+ for
glycolysis.
Figure 6.13 B Fermentation
Figure 6.14 Relationships among the Major Metabolic Pathways of the Cell
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Catabolism:
Polysaccharides are hydrolyzed to glucose,
which enter glycolysis.
Lipids break down to fatty acids and glycerol.
Fatty acids can be converted to acetyl CoA.
Proteins are hydrolyzed to amino acids that can
feed into glycolysis or the citric acid cycle.
How DO cells break down a triglyceride to produce
ATP?
b-oxidation!
http://higheredbcs.wiley.com/legacy/college/pratt/0471393878/st
udent/animations/fatty_acid/index.html
Concept 6.4 Catabolic and Anabolic Pathways Are Integrated
Anabolism:
Many catabolic pathways can operate in reverse.
Gluconeogenesis—citric acid cycle and
glycolysis intermediates can be reduced to
form glucose.
Acetyl CoA can be used to form fatty acids.
Some citric acid intermediates can form nucleic
acids.
The control of cellular respiration
Concept 6.5 During Photosynthesis, Light Energy
Is Converted to Chemical Energy
Photosynthesis involves two pathways:
Light reactions convert light energy into
chemical energy (in ATP and the reduced
electron carrier NADPH).
Carbon-fixation reactions use the ATP and
NADPH, along with CO2, to produce
carbohydrates.
Figure 6.15 An Overview of Photosynthesis
Concept 6.5 During Photosynthesis, Light Energy
Is Converted to Chemical Energy
Light is a form of electromagnetic radiation,
which travels as a wave but also behaves as
particles (photons).
Photons can be absorbed by a molecule, adding
energy to the molecule—it moves to an excited
state.
Figure 6.16 The Electromagnetic Spectrum
Figure 10.6 Why leaves are green: interaction of light with chloroplasts
Concept 6.5 During Photosynthesis, Light Energy
Is Converted to Chemical Energy
Pigments: molecules that absorb wavelengths in
the visible spectrum.
Chlorophyll absorbs blue and red light; the
remaining light is mostly green.
Absorption spectrum—plot of light energy
absorbed against wavelength.
Action spectrum—plot of the biological activity
of an organism against the wavelengths to
which it is exposed
Determining an absorption spectrum
Figure 6.17 Absorption and Action Spectra
Evidence that chloroplast pigments participate in photosynthesis: absorption and
action spectra for photosynthesis in an alga
Figure 6.18 The Molecular Structure of Chlorophyll (Part 1)
Figure 6.18 The Molecular Structure of Chlorophyll (Part 2)
Excitation of isolated chlorophyll by light
Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
A mechanical analogy for the light reactions
Concept 6.5 During Photosynthesis, Light Energy
Is Converted to Chemical Energy
ATP is needed for carbon-fixation pathways.
Cyclic electron transport uses only
photosystem I and produces ATP; an electron
is passed from an excited chlorophyll and
recycles back to the same chlorophyll.
Cyclic electron flow
The light reactions and chemiosmosis: the organization of the thylakoid membrane
Figure 6.21 The Calvin Cycle
Concept 6.6 Photosynthetic Organisms Use Chemical Energy
to Convert CO2 to Carbohydrates
1. Fixation of CO2:
CO2 is added to ribulose 1,5-bisphosphate
(RuBP).
Ribulose bisphosphate
carboxylase/oxygenase (rubisco) catalyzes
the reaction.
A 6-carbon molecule results, which quickly
breaks into two 3-carbon molecules: 3phosphoglycerate (3PG).
Figure 6.22 RuBP Is the Carbon Dioxide Acceptor
Concept 6.6 Photosynthetic Organisms Use Chemical Energy
to Convert CO2 to Carbohydrates
2. 3PG is reduced to form glyceraldehyde 3phosphate (G3P).
C4 leaf anatomy and the C4 pathway
C4 and CAM photosynthesis compared
A review of photosynthesis