Chapter Outline

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Chapter Outline
15.1 Metabolic Pathways, Energy, and Coupled
Reactions 15.2 Overview of Metabolism 15.3
Digestion 15.4 Glycolysis 15.7 Citric Acid
Cycle 15.8 Electron Transport Chain and Oxidative
Phosphorylation 15.9 Lipid Metabolism 15.10 Amino
Acid Metabolism
15.5 Gluconeogenesis 15.6 Glycogen Metabolism
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• To discuss how living things manufacture or break
  down carbohydrates, lipids, or members of any
  other biochemical class of compounds it is
  necessary to talk in terms of groups of reactions
  called metabolic pathways.
• The metabolic pathways can be
• 1) linear a continuous series of reactions in
  which the product of one reaction is the reactant
  in the next.
• 2) circular a series of reactions where the
  final product is an initial reactant.
• 3) spiral a series of repeated reactions is
  used to break down or build up a molecule.

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15.1 Metabolic Pathways, Energy, and Coupled
Reactions
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Coupled Rxn
In a coupled reaction, a spontaneous reaction
provides the energy needed to a nonspontaneous
reaction.

• Fructose 6-phosphate Pi ? fructose
  1,6-biphosphate H20
• (?G 3.9 kcal/mol)
• 2. ATP H2O ? ADP Pi (?G -7.3
  kcal/mol)
• Overall
• Fructose 6-phosphate ATP ? fructose
  1,6-biphosphate ADP
• (?G -3.4 kcal/mol)
• Is the coupled reaction spontaneous or
  nonspontaneous?

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15.2 Metabolism, the sum of all reactions that
take place in a living thing, can be divided into
two parts

1. Catabolism. During catabolism, compounds are
   broken down into smaller ones in processes that,
   usually, release energy.
2. Anabolism. Anabolism involves the biosynthesis
   of larger compounds from smaller ones in
   processes that, usually, require energy.

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-ADP and ATP are key players in
metabolism. -Energy released during catabolism is
used to drive the formation of these two
compounds. -Energy obtained by hydrolyzing ATP
can, in turn, be used for anabolism or other
energy requiring processes, such as muscle
contraction.
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Catabolism (break down of large molecules to
small ones.)
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Catabolism

• Not all catabolic pathways take place in the same
  part of a cell.
• Cytoplasm
• glycolysis
• Mitochondria
• Fatty acid oxidation
• Amino acid catabolism
• Citric acid cycle
• Electron transport chain
• Oxidative phosphorylation

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Anabolism

• During anabolism, small molecules such as
  pyruvate, acetyl-CoA, and intermediates in the
  citric acid cycle are used to make fatty acids,
  monosaccharides, and amino acids for
  incorporation into lipids, polysaccharides, and
  proteins.

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15.3 Digestion
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Example of polysaccharide break down to
monosaccharide.
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Example of triglyceride and polypeptide break
down.
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15.4 Glycolysis
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15.4 Glycolysis

• The net reaction for glycolysis is
• Glucose 2NAD 2ADP 2Pi ?
• 2 pyruvate 2NADH 2ATP energy

Energy and Glycolysis
glucose 2ADP 2Pi ? 2lactate 2ATP
?G -29.4 kcal/mol
spontaneous
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• Metabolism can take pyruvate into a number of
  different directions.
• In yeast, pyruvate undergoes alcoholic
  fermentation.
• In this process pyruvate is split into
  acetaldehyde plus CO2, and acetaldehyde is
  reduced to ethanol.
• These reactions serve to recycle NADH back into
  NAD, allowing glycolysis to continue.

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• In humans, pyruvate is reduced to lactate when
  conditions are anaerobic (O2 deficient)
• This reaction converts NADH back into NAD,
  allowing glycolysis to continue.
• Once produced, lactate is sent in blood to the
  liver, where it can be used to make glucose.
• Under aerobic conditions (O2 is in sufficient
  supply), pyruvate is converted into acetyl-CoA,
  the reactant for the first step in the citric
  acid cycle.
• Glycolysis takes place in a cells cyctoplasm,
  but the formation of acetyl-CoA and the citric
  acid cycle take place inside the mitochondria.

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15.7 Citric Acid Cycle
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15.7 Citric Acid Cycle
Overall Rxn (occurs twice)

• Acetyl-CoA 3NAD FAD GDP Pi ? 2CO2 CoA
  3NADH FADH2 GTP

?G -11 kcal/mol
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15.8 Electron Transport Chain and Oxidative
Phosphorylation

• The electron transport chain is a group of
  proteins and other molecules embedded in the
  inner mitochondrial membrane.

The electron transport chain and oxidative
phosphorylation use the potential energy present
in NADH and FADH2 to make ATP.
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Summary of Glucose catabolism
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15.9 Lipid Metabolism
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Four reactions in the b-oxidation of a fatty acid
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b-oxidation Spiral of a fatty acid
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Fatty Acid Catabolism

• One common fate of fatty acids is their use as
  reactants in the formation of triglycerides,
  sphingolipids, and other lipids that contain
  fatty acid residues.
• Their other important use is as a source of
  energy.
• Fatty acid catabolism involves a spiral metabolic
  pathway, called the ? oxidation spiral, where the
  same series of reactions is repeated on
  increasingly shorter reactants.

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15.10 Amino Acid Metabolism

• Removal of the amino group is an important part
  of amino acid catabolism.
• The two reactions most often used to do this are
• 1) Transamination is the transfer of an amino
  group from an amino acid to an ?-keto acid.
  These reactions are catalyzed by transaminase
  enzymes.
• 2) In oxidative deamination an amino group is
  replaced by a carbonyl (CO) group.

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Amino Acid Anabolism

• Of the 20 amino acids used to synthesize
  proteins, humans can make only half.
• The others, called essential amino acids, must be
  obtained in the diet.

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15.5 Gluconeogenesis

• Gluconeogenesis, the pathway involved in making
  glucose from noncarbohydrate sources, such as
  amino acids, glycerol, and lactate, takes place
  mostly in the liver.
• One important role of this process is the
  conversion of lactate produced during anaerobic
  catabolism back into glucose, which is either
  transformed into glycogen or goes into the blood
  and is transported to other cells.

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• In addition to recycling lactate, gluconeogenesis
  is a provider of glucose during fasting or in the
  early stages of starvation, in which glucose and
  glycogen (a source of glucose) have been
  depleted.
• The supply of glucose is especially important to
  brain cells, which use only glucose to fuel
  metabolism, unlike other cells in the body which
  can also use lipids and proteins.

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15.5 Gluconeogenesis
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15.6 Glycogen Metabolism

• Glycogen, a highly branched homopolysaccharide,
  is found mainly in liver and muscle cells.
• This carbohydrate is a glucose storage molecule
  that, when necessary, can be quickly broken down
  to release glucose.
• Glycogen is synthesized from or is broken down
  into glucose 6-phosphate.

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15.6 Glycogen Metabolism