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Cellular Respiration
Breathe in… breathe out… or not!
Boehm 2016
Introduction
• Living is work.
• To perform their many tasks,
cells require energy from
outside sources.
• In most ecosystems, energy
enters as sunlight.
• Light energy trapped in
organic molecules (such as
glucose) is available to both
photosynthetic organisms
(autotrophs) and others
that eat them
(heterotrophs).
Fig. 9.1
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Chloroplast
Chloroplast
• Chloroplasts, found in plants and eukaryotic
algae, are the site of photosynthesis.
• They convert solar energy to chemical energy and
synthesize new organic compounds from CO2 and
H2O.
• Contains chlorophyll, which causes the green
color of many plants.
• Has small quantities of DNA that help make
own proteins.
Mitochondria
Mitochondria
• Mitochondria is the organelle that converts
energy to forms that cells can use for work“powerhouse”.
• Mitochondria are the sites of cellular
respiration, generating ATP from the
catabolism of sugars, fats, and other fuels in the
presence of oxygen.
• Has small quantities of DNA that help make
own proteins.
• The DNA is passed on from mother to childmaternity testing possible.
Respiration involves glycolysis, the Krebs cycle,
and electron transport: an overview
• Respiration occurs in three metabolic stages:
1. glycolysis,
2. the Krebs cycle
3. the electron
transport
chain (oxidative
phosphorylation).
• NET 36 ATP formed
• Total 38 ATP formed
Fig. 9.6
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• ATP (adenosine triphosphate) is a type of
nucleotide consisting of the nitrogenous base
adenine, the sugar ribose, and a chain of three
phosphate groups.
Fig. 6.8a
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• The bonds between phosphate groups can be broken
by hydrolysis.
• Hydrolysis of the end phosphate group forms adenosine
diphosphate [ATP -> ADP + Pi] and releases energy.
• ATP is a renewable resource that is continually regenerated by
adding a phosphate group to ADP (the reaction can go forward
and reverse).
Fig. 6.8b
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Fig. 9.16
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Reflect and Review
• Why does a cell need ATP?
• Where does glycolysis happen in a cell?
• Where does the rest of CR happen in a cell?
Glycolysis
• Glycolysis occurs in the cytoplasm.
• Breaks glucose into two molecules of pyruvate.
• Happens WITHOUT oxygen!
• Some ATP is generated in
glycolysis by substrate-level
phosphorylation.
• Here an enzyme
transfers a phosphate
group from an
organic molecule
(the substrate)
to ADP, forming
ATP.
Fig. 9.7
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• In the energy investment phase, ATP provides activation
energy by phosphorylating glucose (phosphorylation makes
a molecule less stable- easier to break apart).
• This requires 2 ATP per glucose.
• In the energy payoff
phase, ATP is
produced by
substrate-level
phosphorylation
and NAD+ is
reduced to NADH.
• 2 ATP (net) and
2 NADH are produced
per glucose.
Fig. 9.8
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Fig. 9.9a
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Fig. 9.9b
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Fermentation enables some cells to produce
ATP without the help of oxygen
• Glycolysis generates 2 ATP whether oxygen is present
(aerobic) or not (anaerobic).
• Fermentation can generate ATP from glucose as long as
there is a supply of NAD+ to accept electrons.
• If the NAD+ pool is exhausted, glycolysis shuts down.
• Under aerobic conditions, NADH transfers its electrons to
the electron transfer chain, recycling NAD+.
• Under anaerobic conditions, and depending on the type of
organism, either lactic acid or alcoholic fermentation will
occur to produce ATP.
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• In alcohol fermentation, pyruvate is converted
to ethanol in two steps.
• First, pyruvate is converted to a two-carbon
compound, acetaldehyde by the removal of CO2.
• Second, acetaldehyde is reduced by NADH to
ethanol.
• Alcohol fermentation
by yeast is used in
brewing and
winemaking.
Fig. 9.17a
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• During lactic acid fermentation, pyruvate is
reduced directly by NADH to form lactate
(ionized form of lactic acid).
• Lactic acid fermentation by some fungi and bacteria
is used to make cheese and yogurt.
• Muscle cells switch from aerobic respiration to lactic
acid fermentation to generate ATP when O2 is scarce.
• The waste product,
lactate, may cause
muscle fatigue, but
ultimately it is
converted back to
pyruvate in the liver.
Fig. 9.17b
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• Some organisms (facultative anaerobes), including yeast
and many bacteria, can survive using either fermentation or
respiration.
• At a cellular level, human
muscle cells can behave
as facultative anaerobes,
but nerve cells cannot.
• For facultative anaerobes,
pyruvate can lead to either
anaerobic or aerobic
respiration.
Fig. 9.18
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Aerobic Respiration: The Krebs cycle
completes the energy-yielding oxidation of
organic molecules: a closer look
• More than three quarters of the original energy in
glucose is still present in two molecules of
pyruvate.
• If oxygen is present, pyruvate enters the
mitochondrion where enzymes of the Krebs
cycle complete the oxidation of the organic fuel to
carbon dioxide and the energy stored in NADH
can be converted to ATP .
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• The conversion of
pyruvate and the
Krebs cycle
produces large
quantities of
electron carriers.
• Each cycle produces
one ATP, three NADH,
and one FADH2
(another electron
carrier) per acetyl
CoA.
• Happens in the matrix
Fig. 9.12
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Electron transport chain ATP
synthesis: a closer look
• The vast majority of the ATP (34) comes from the
energy in the electrons carried by NADH (and
FADH2).
• The energy in these electrons is used in the
electron transport system to power ATP
synthesis.
• Thousands of the electron transport chain are
found in the extensive surface of the inner
membrane of the mitochondrion (cristae).
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Fig. 9.15
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• A protein complex, ATP
synthase, in the cristae
actually makes ATP
from ADP and Pi.
• ATP used the energy of
an existing proton
gradient to power ATP
synthesis.
• This proton gradient
develops between the
intermembrane space
and the matrix.
Fig. 9.14
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• Carbohydrates, fats,
and proteins can all
be catabolized
through the same
pathways.
Fig. 9.19
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Fig. 9.16
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Reflect and review
• Compare aerobic and anaerobic respiration.
What are the similarities and differences? Is
one better than the other?
• Where is the most ATP made in aerobic
respiration? Why is so much ATP made there?
• Compare and contrast the electron transport
chains from photosynthesis and cell
respiration. Discuss similarities and
differences.