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Chapter 5
Cell Respiration and
Metabolism
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Metabolism
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All reactions that involve energy
transformations.
Divided into 2 Categories:
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Catabolic:
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Release energy.
Breakdown larger molecules into smaller
molecules.
Anabolic:
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Require input of energy.
Synthesis of large energy-storage molecules.
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Aerobic Cell Respiration
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Oxidation-reduction reactions:
Break down of molecules for energy.
 Electrons are transferred to
intermediate carriers, then to the
final electron acceptor: oxygen.
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Oxygen is obtained from the blood.
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Glycolysis
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Breakdown of glucose for energy in the
cytoplasm.
Glucose is converted to 2 molecules of
pyruvic acid (pyruvate).
Each pyruvic acid contains:
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3 carbons
3 oxygens
4 hydrogens
4 hydrogens are removed from intermediates.
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Glycolysis
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Each pair of H+ reduces a molecule of
NAD.
Produces:
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2 molecules of NADH and 2 unbound H+
2 ATP
Glycolysis Pathway:
Glucose + 2 NAD + 2 ADP + 2 Pi
2 pyruvic acid + 2 NADH and 2 ATP
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Glycolysis
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Glycolysis is exergonic.
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Energy released used to drive endergonic
reaction:
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ADP + Pi
ATP
Glucose must be activated first before
energy can be obtained.
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ATP consumed at the beginning of
glycolysis.
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Glycolysis
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ATP
ADP + Pi
Pi is not released but added to
intermediate molecules
(phosphorylation).
Phosphorylation of glucose, traps the
glucose inside the cell.
Net gain of 2 ATP and 2 NADH.
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Glycolysis
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Lactic Acid Pathway
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Anaerobic respiration:
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Oxygen is not used in the process.
NADH + H+ + pyruvic acid
lactic acid and NAD.
Produce 2 ATP/ glucose molecule.
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Lactic Acid Pathway
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Some tissues adapted to anaerobic
metabolism:
Skeletal muscle: normal daily
occurrence.
 RBCs do not contain mitochondria
and only use lactic acid pathway.
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Cardiac muscle: ischemia
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Glycogenesis and
Glycogenolysis
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Increase glucose intracellularly,
would increase osmotic pressure.
Must store carbohydrates in form of
glycogen.
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Glycogenesis: formation of glycogen from glucose.
Glycogenolysis: conversion of glycogen to glucose-6phosphate.
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Glucose-6-phosphate can be utilized through glycolysis.
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Glycogenesis and
Glycogenolysis
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Glucose-6-phosphate cannot leak out of
the cell.
Skeletal muscles generate glucose-6phosphate for own glycolytic needs.
Liver contains the enzyme glucose-6phosphatase that can remove the
phosphate group and produce free
glucose.
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Cori Cycle
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Lactic acid produced by anaerobic respiration
delivered to the liver.
LDH converts lactic acid to pyruvic acid.
Pyruvic acid converted to glucose-6phosphate:
 Intermediate for glycogen.
 Converted to free glucose.
Gluconeogenesis: conversion to noncarbohydrate molecules through pyruvic acid
to glucose.
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Aerobic Respiration
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Aerobic respiration of glucose,
pyruvic acid is formed by
glycolysis, then converted into
acetyl coenzyme A (acetyl CoA).
Energy is released in oxidative
reactions, and is captured as ATP.
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Aerobic Respiration
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Pyruvic acid enters interior of
mitochondria.
Converted to acetyl CoA and 2 C02.
Acetyl CoA serves as substrate for
mitochondrial enzymes.
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Acetyl CoA enters the Krebs Cycle.
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overview
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Krebs Cycle
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Acetyl CoA combines with oxaloacetic
acid to form citric acid.
Citric acid enters the Krebs Cycle.
Produces oxaloacetic acid to continue
the pathway.
1 GTP, 3 NADH, and 1 FADH2
NADH and FADH2 transport electrons to
Electron Transport Cycle.
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CAC
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Electron Transport
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Cristae of inner mitochondrial
membrane contain molecules that
serve as electron transport system.
Electron transport chain consists of
FMN, coenzyme Q, and
cytochromes.
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ETC Chain
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Each cytochrome transfers electron pairs
from NADH and FADH2 to next
cytochrome.
Oxidized NAD and FAD are regenerated
and shuttle electrons from the Krebs
Cycle to the ETC.
Cytochrome receives a pair of electrons.
Iron reduced, then oxidized as electrons
are transferred.
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ETC Chain
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Cytochrome a3 transfers electrons
to O2 (final electron acceptor).
Oxidative phosphorylation occurs:
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Energy derived is used to
phosphorylate ADP to ATP.
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Coupling ETC to ATP
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Chemiosmotic theory:
ETC powered by transport of
electrons, pumps H+ from
mitochondria matrix into space
between inner and outer
mitochondrial membranes.
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Coupling ETC to ATP
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Proton pumps:
NADH-coenzyme Q reductase complex:
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Cytochrome C reductase complex:
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Transports 4 H+ for every pair of electrons.
Transports 4 H+.
Cytochrome C oxidase complex:
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Transports 2 H+.
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Coupling ETC to ATP
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Higher [H+] in inter-membrane space.
Respiratory assemblies:
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Permit the passage of H+.
Phosphorylation is coupled to oxidation,
when H+ diffuse through the respiratory
assemblies:
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ADP and Pi
ATP
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Coupling ETC to ATP
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Oxygen functions as the last
electron acceptor.
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Oxidizes cytochrome a3.
Oxygen accepts 2 electrons.
O2 + 4 e- + 4 H+
2 H20
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ATP Produced
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Direct phosphorylation:
Glycolysis:
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2 ATP
Oxidative phosphorylation:
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2.5 ATP produced for pair of electrons
each NADH donates.
1.5 ATP produced for each pair of
electrons FADH2 donates ((activates 2nd
and 3rd proton pumps).
26 ATP produced.
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Metabolism of Lipids
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When more
energy is taken
in than
consumed,
glycolysis
inhibited.
Glucose
converted into
glycogen and fat.
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Lipogenesis
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Formation of
fat.
Occurs mainly
in adipose
tissue and liver.
Acetic acid
subunits from
acetyl CoA
converted into
various lipids.
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Metabolism of Lipids
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Lipolysis:
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Breakdown of fat.
Triglycerides
lipase
glycerol + fa
Free fatty acids (fa) serve as bloodborne energy carriers.
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Beta-oxidation
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Enzymes
remove
2-carbon
acetic acid
molecules
from acid end
of fa.
Forms acetyl
CoA.
Acetyl CoA
enters Krebs
Cycle.
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Metabolism of Proteins
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Nitrogen is ingested primarily as protein.
Excess nitrogen must be excreted.
Nitrogen balance:
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Amount of nitrogen ingested minus amount
excreted.
+ N balance:
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Amount of nitrogen ingested more than amount excreted.
- N balance:
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Amount of nitrogen excreted greater than ingested.
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Adequate amino acids are required for growth and repair. A
new amino acid can be obtained by:
Transamination:
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Amino group (NH2) transferred from one amino acid to form another.
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Process by which excess amino acids are
eliminated.
Amine group from glutamic acid removed, forming
ammonia and excreted as urea.
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Deamination
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Energy
conversion:
amino acid is
deaminated.
Ketoacid can
enter the Krebs
Cycle.
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Use of different energy sources.