Transcript Ch15 Lect F09

Chapter Outline
15.1 Metabolic Pathways, Energy,
and Coupled Reactions
15.5 Gluconeogenesis
15.6 Glycogen Metabolism
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
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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.
1. 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.
1) Cytoplasm
•
glycolysis
2) Mitochondria
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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 cell’s 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 b 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 (C=O) 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
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•
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
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