Download 1. What is the source of our energy, and what is its fate in the body

Chapter 21: The Generation of Biochemical Energy
1.!
What is the source of our energy, and what is its fate in the body? Be able to
provide an overview of the sources of our energy and how we use it, identify the
cellular location of energy generation, and explain the significance of exergonic and
endergonic reactions in metabolism.!
2.!
How are the reactions that break down food molecules organized? Be able to list
the stages in catabolism and describe the role of each.!
3.!
What are the major strategies of metabolism? Be able to explain and give
examples of the roles of ATP, coupled reactions, and oxidized and reduced coenzymes
in metabolic pathways.
4.!
What is the citric acid cycle? Be able to describe what happens in the citric acid
cycle and explain its role in energy production.!
5.!
How is ATP generated in the final stage of catabolism? Be able to describe in
general the electron-transport chain, oxidative phosphorylation , and how they are
coupled.!
6.
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What are the harmful by-products produced from oxygen, and what protects
against them? Be able to identify the highly reactive oxygen-containing products
formed during metabolism and the enzymes and vitamins that counteract them.
Chapter 21: The Generation of Biochemical Energy
1.!
What is the source of our energy, and what is its fate in the body?
Energy and Life
Energy must be released from food gradually.
Energy must be stored in readily accessible forms.
Release of energy from storage must be finely controlled so that it is available exactly when
and where it is needed.
Just enough energy must be released as heat to maintain constant body temperature.
Energy and Biochemical Reactions
Exergonic:
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Endergonic:
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Chapter 21: The Generation of Biochemical Energy
Prokaryotic Cells:
Eukaryotic Cells:
Cell Components and Their Principal Function:
Cilia:
Golgi Apparatus:
Rough Endoplasmic Reticulum:
Nucleus:
Ribosome:
Microvilli:
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Chapter 21: The Generation of Biochemical Energy
Lysosome:
Smooth Endoplasmic Reticulum:
Cell Membrane:
Cytoplasm:
Cytosol:
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Chapter 21: The Generation of Biochemical Energy
Mitochondrion:
Mitochondrial Matrix:
Adenosine triphosphate (ATP):
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Chapter 21: The Generation of Biochemical Energy
2.!
How are the reactions that break down food molecules organized? Catabolism:
Anabolism:
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Chapter 21: The Generation of Biochemical Energy
Stage 1: Digestion Enzymes in saliva, the stomach, and the small
intestine convert the large molecules of lipids, carbohydrates, and
proteins to smaller molecules.
Carbohydrates are broken down to glucose and other sugars, proteins
are broken down to amino acids, and triacylglycerols , the lipids
commonly known as fats and oils, are broken down to glycerol plus
long-chain carboxylic acids, the fatty acids.
These smaller molecules are transferred into the blood for transport to
cells throughout the body.
Stage 2: Acetyl-S-coenzyme A production The small molecules from
digestion follow separate pathways that move their carbon atoms
into two-carbon acetyl groups. The acetyl groups are attached to
coenzyme A by a bond between the sulfur atom of the thiol group at
the end of the coenzyme A molecule and the carbonyl C atom of
the acetyl group.
Stage 3: Citric acid cycle Within mitochondria, the acetyl-group
carbon atoms are oxidized to the carbon dioxide that we exhale.
Most of the energy released in the oxidation leaves the citric acid
cycle in the chemical bonds of reduced coenzymes.
Stage 4: ATP production Electrons from the reduced coenzymes are
passed from molecule to molecule down an electron-transport
chain. Along the way, their energy is harnessed to produce more
ATP. At the end of the process, these electrons— along with
hydrogen ions from the reduced coenzymes—combine with oxygen
we breathe to produce water.
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Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
3.!
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What are the major strategies of metabolism? Chapter 21: The Generation of Biochemical Energy
Oxidation:
Reduction:
Oxidation and reduction always occur together
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Chapter 21: The Generation of Biochemical Energy
A steady supply of oxidizing and reducing agents must be available, so
a few coenzymes continuously cycle between their oxidized and
reduced forms.
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Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
4.!
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What is the citric acid cycle? Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
The net result of the citric acid cycle is:
Production of four reduced coenzyme molecules, 3 NADH and 1
FADH2
Conversion of an acetyl group to two CO2 molecules
Production of one energy-rich molecule (GTP)
ADP acts as an allosteric activator for the enzyme for Step 3. NADH
acts as an inhibitor of the enzyme for Step 3.
By such feedback mechanisms, the cycle is activated when energy is
needed and inhibited when energy is in good supply.
5.!
How is ATP generated in the final stage of catabolism? At the conclusion of the citric acid cycle, the reduced coenzymes formed
in the cycle are ready to donate their energy to making additional
ATP
Hydrogen and electrons from NADH and FADH2 enter the electrontransport chain at enzyme complexes I and II, respectively.
The enzyme for Step 6 of the citric acid cycle is part of complex II.
FADH2 produced there does not leave complex II. Instead it is
immediately oxidized there by reaction with coenzyme Q.
Following formation of the mobile coenzyme Q, reductions occur when
electrons are transferred.
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Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
ATP Synthase:
Oxidative phosphorylation:
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Chapter 21: The Generation of Biochemical Energy
6.!
What are the harmful by-products produced from oxygen, and what protects
against them?
More than 90% of the oxygen we breathe is used in electron transport–
ATP synthesis reactions.
In these and other oxygen-consuming redox reactions, the product
may not be water, but one or more of three highly reactive species.
The superoxide ion, !O2- , and the hydroxyl free radical, !OH, can grab
an electron from a bond in another molecule, which results in
breaking that bond. The third oxygen by-product is hydrogen
peroxide, H2 O2 , a relatively strong oxidizing agent.
Conditions that can enhance production of these three reactive oxygen
species are represented in the drawing below. Some causes are
environmental, such as exposure to smog or radiation. Others are
physiological, including aging and inflammation.
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Chapter 21: The Generation of Biochemical Energy
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Chapter 21: The Generation of Biochemical Energy
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