Cellular respiration

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Cellular respiration Energy is stored in
chemical bonds potential energy covalent
bonds Energy is released when these bonds are
broken catabolism some is used for work, the
rest is lost fermentation- no oxygen
present aerobic respiration
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How is this energy put to work? Through ATP (see
slide for review)
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Energy is released in a controlled
manner through redox reactions Oxidation one
reactant loses electrons Reduction the other
reactant gains electrons Rather than combusting,
glucose is converted to CO2 and water through a
series of reactions C6H12O6 6O2 ? 6CO2 6H2O
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Coenzymes like NAD serve as electron acceptors
(coenzymes tend to function as electron
carriers). They are recycled so exist at low
concentrations Oxygen is the terminal electron
acceptor in aerobes
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Chemotrophs- organisms that oxidize
food molecules Such as? glucose principal
blood sugar in vertebrates breakdown product
of starch breakdown product of sucrose Process
is highly exergonic ?Go is 686 kcal/mol when
completely oxidized Biological oxidation is
controlled
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Aerobic respiration yields much more energy from
a molecule of glucose than does anaerobic
respiration Aerobic respiration terminal
electron acceptor is oxygen (forms H2O) If
oxygen is not present glycolysis takes
place end product (pyruvate) is converted to an
end product and NAD is recycled
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Different organisms have different
pathways Animal cells lactate is end
product (lactate fermentation) Plants and
yeast ethanol and CO2 (alcoholic
fermentation) Energy can be obtained more
rapidly but a lot of sugar must be consumed to
get it
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Organisms are aerobes, facultative anaerobes or
obligate anaerobes Obligate aerobes require
oxygen Obligate anaerobes are actually poisoned
by oxygen Facultative anaerobes can function
either way some tissues within aerobic
organisms can function anaerobically (for awhile)
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Muscle cells can function as facultatively anaero
bic cells for awhile Lactate builds up?
fatigue What happens next Rest/recovery Cori
cycle
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Other organisms (mainly microbial) use other
fermentation pathways, named by end product
(formed from pyruvic acid) Propionate
(cheesemaking) Butylene glycol butyrate (food
spoilage) Acetone Isopropyl alcohol, etc.
Depends on the enzymes! All regenerate NAD
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Some of these are commercially important products
How must organisms be cultivated to
produce these products?
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Obligate (strict) anaerobes use
different electron acceptors Sulfur
(H2S) Protons (H2O) Ferric ions
(Fe2) Pathways help cycle these elements in the
environment Where are they found in the
environment?
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Glycolysis converts a molecule of glucose
into two molecules of pyruvate Takes place in
the cytosol of cells Electron carriers
(NAD) Substrate-level phosphorylation
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Glucose is not the only substrate for
glycolysis Substrates are converted into
intermediates in the pathway ASAP Sugars fructo
se, galactose, mannose (hexoses) Milk sugar
(lactose) is a disaccharide of glucose and
galactose Galactose is phosphorylated and
converted to glucose Lack of enzyme
galactosemia
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Pentoses (5-carbon sugars) can also be used if
converted to hexoses phosphogluconate
pathway Glucose is usually stored as
polysaccharide (name?) broken off by process
requiring phosphor- ylation (glucose-1-P) Phospho
glucomutase converts to G-6-P feeds into
glycolysis
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Gluconeogenesis Synthesis of glucose and other
cabohydrates from noncarbohydrate
precursors Often starts from lactate or
pyruvate Some reactions in glycolysis are
reversible Bypasses the most highly exergonic
reactions ATP and GTP are hydrolyzed, so
overall pathway is exergonic
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Glycolysis and gluconeogenesis are
regulated depending on cells needs Allosteric
regulation of unique enzymes Phosphofructokinase
in glycolysis regulated by ATP (-) AMP
() ADP () citrate (-) Pyruvate carboxylase
(builds back pyruvate) activated by abundant
acetyl CoA
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Also regulated by hormones Glucagon
Epinephrine raise cyclic AMP (cAMP) Stimulate
gluconeogenesis (need more blood sugar) Also
inhibits glycogen formation, for the
same reason Gluconeogenesis pathways vary
among organisms
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What happens next? If oxygen is present,
pyruvate moves into the Krebs cycle