Ch 9: Cellular Respiration
Chapter 9: Cellular Respiration
From Topic 2.1
• Anabolism is the synthesis of complex molecules from simpler molecules
including the formation of macromolecules from monomers by condensation
• Catabolism is the breakdown of complex molecules into simpler molecules
including the hydrolysis of macromolecules into monomers.
Aim 8: The ethics of the use of animals in experiments could be
discussed in relation to respirometer experiments. Large-scale use
of food plants for biofuels and the resulting impact on food prices
has ethical implications.
From Topic 8.2
Nature of science: Paradigm shift—the chemiosmotic theory led
to a paradigm shift in the field of bioenergetics (2.3)
From Topic 2.8
Essential idea: Cell respiration supplies energy for the functions of life.
• Cell respiration involves the oxidation and reduction of electron
Nature of science: Assessing the ethics of scientific research—the use of
invertebrates in respirometer experiments has ethical implications (4.5).
• Phosphorylation of molecules makes them less stable.
Skill: Analysis of results from experiments involving measurement of
• Energy released by oxidation reactions is carried to the cristae of
respiration rates in germinating seeds or invertebrates using a respirometer. the mitochondria by reduced NAD and FAD.
• The structure of the mitochondrion is adapted to the function it
• Cell respiration is the controlled release of energy from organic compounds performs.
to produce ATP.
• In glycolysis, glucose is converted to pyruvate in the cytoplasm.
• ATP from cell respiration is immediately available as a source of energy in • Glycolysis gives a small net gain of ATP without the use of
the cell.
• Anaerobic cell respiration gives a small yield of ATP from glucose.
• In aerobic cell respiration pyruvate is decarboxylated and
• Aerobic cell respiration requires oxygen and gives a large yield of ATP from oxidized, and converted into acetyl compound and attached to
coenzyme A to form acetyl coenzyme A in the link reaction.
Applications and skills:
• In the Krebs cycle, the oxidation of acetyl groups is coupled to
• Application: Use of anaerobic cell respiration in yeasts to produce ethanol the reduction of hydrogen carriers, liberating carbon dioxide.
and carbon dioxide in baking.
• Transfer of electrons between carriers in the electron transport
• Application: Lactate production in humans when anaerobic respiration is
chain in the membrane of the cristae is coupled to proton
used to maximize the power of muscle contractions.
• In chemiosmosis protons diffuse through ATP synthase to
• Details of the metabolic pathways of cell respiration are not needed but the generate ATP.
substrates and final waste products should be known.
• Oxygen is needed to bind with the free protons
• There are many simple respirometers which could be used. Students are
expected to know that an alkali is used to absorb CO2, so reductions in
volume are due to oxygen use. Temperature should be kept constant to avoid
volume changes due to temperature fluctuations.
Chapter 9: Cellular Respiration
From Topic 8.2
• The names of the intermediate compounds in gylcolysis and the Krebs cycle are not required.
Applications and skills:
• Application: Electron tomography used to produce images of active mitochondria.
• Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation
reactions occur.
• Skill: Annotation of a diagram of a mitochondrion to indicate the adaptations to its function.
Catabolism: breaking of
large molecules to smaller
molecules, as a result it
releases stored energy
C6H12O6 + 6O2  6 CO2 +
6 H2O + energy (ATP) and
• Efficiency
• Cell @ 40%
• Car @ 20%
How Energy is Transferred
• Energy is transferred in the form of electrons
• Electrons are transferred through hydrogens (it is the
mechanism for electron transfer)
• Some energy is stored as phosphate bonds in ATP
• Hydrogen carriers (NAD+) shuttle electrons in oxidationreduction reactions
- Loss of e- is oxidation
- Gain of e- is reduction.
Electron Carriers: NADH and FADH2
Generating Energy in the form of ATP
• There are two ways for ATP synthesis:
- Oxidative Phosphorylation: uses energy from a series
of redox reactions that occurs in the electron transport chain
to produce ATP
- Substrate Level Phosphorylation: when an enzyme
transfers a phosphate group from a substrate molecule to ADP
forming ATP
Fuel For Respiration
Food is the source of energy (digestion)
Ultimately the source of energy for cell respiration
comes from photosynthesis, when plants produces
Other Sources of “Fuel”
• Glucose is the best fuel
• Polysaccharides are broken to release glucose
• Proteins can be broken down to be Amino acids and then
converted to intermediate products that are broken down
in Krebs.
• Lipids are broken down to glycerol (to Glycolysis) and fatty
acids (to Krebs)
Stages of Cellular Respiration
• There are three main stages:
• Glycolysis
• Krebs Cycle (Citric Acid Cycle)
• Electron Transport (Chemiosmosis)
• Glycolysis: “splitting of
sugar” occurs in the
Must invest 2 ATP’s first
Produces 4 ATP’s at the
end, but a net gain of 2
Followed by “prep”
step, when acetyl CoA
turns to pyruvate
(pyruvic acid)
• Glycolysis: can occur
with or without O2; but
the process itself
doesn’t require O2
“Prep” Step
• “Prep” Step: this is not the official name! but we can’t find a
better name for it. Hahah…
The conversion of pyruvate to acetyl CoA before entering the Citric Acid
Cycle (aka Krebs/tricarboxylic acid cycle (TCA))
Produces two NADH (since there’s two pyruvates that enter and two
acetyl CoA’s that comes out
Citric Acid Cycle
• Citric Acid Cycle:
- Occurs in the
mitochondrial matrix
- For each Acetyl CoA, 3
NADH, 1 FADH2 1 ATP, 2
CO2 are produced.
Electron Transport Chain and Chemiosmosis
Occurs in the inner membrane of the mitochondria between the matrix and the intermembrane
Transport is carried out by a series of membrane proteins
Some carry just electrons, while others take protons with electrons (H+ and e-)
Produces water and a lot of ATP at the end
Electron Transport Chain and Chemiosmosis
• Chemiosmosis: when energy in the form of H+ ions
gradient across a membrane is used to make ATP
Total Energy Yield
• A review of Cellular Respiration
- What each stage produces and contributes to the total energy
yield from cellular respiration
• Fermentation: w/o O2 Krebs and ETC cannot occur
- It is an extension of glycolysis in anaerobic conditions
- Can produce ATP by substrate level phosphorylation only
- needs to replenish the NAD+ as an e- carrier to keep it going
• There are two types:
- Alcoholic Fermentation
- Lactic Acid Fermentation
• Lactic Fermentation: this causes the pain you feel
after you exercise too much; also used in making cheese
and yogurt
•Alcoholic Fermentation: this is used for brewing ,
winemaking, and baking

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