BIO 311C Lecture 9: Ch 9 Notes
Chapter 9: Cellular Respiration and Fermentation
1) Life Is Work
a) Living cells require energy from outside sources to do work
i) The work of the cell includes assembling polymers, membrane transport, moving, and reproducing
b) Animals can obtain energy to do this work by feeding on other animals or photosynthetic organisms
c) Energy flows into an ecosystem as sunlight and leaves as heat
d) The chemical elements essential to life are recycled
e) Photosynthesis generates O2 and organic molecules, which are used in cellular respiration
f) Cells use chemical energy stored in organic molecules to generate ATP, which powers work
2) Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
a) Catabolic pathways release stored energy by breaking down complex molecules
i) Electron transfer plays a major role in these pathways
ii) These processes are central to cellular respiration
b) Catabolic Pathways and Production of ATP
i) The breakdown of organic molecules is exergonic
ii) Fermentation is a partial degradation of sugars that occurs without O2
iii) Aerobic respiration consumes organic molecules and O2 and yields ATP
(1) Anaerobic respiration is similar to aerobic respiration but consumes compounds other
than O2
iv) Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic
respiration
v) Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration
with the sugar glucose
(1) C6H12O6  6 O2 → 6 CO2  6 H2O  Energy (ATP  heat)
c) Redox Reactions: Oxidation and Reduction
i) The transfer of electrons during chemical reactions releases energy stored in organic molecules
ii) This released energy is ultimately used to synthesize ATP
iii) The Principle of Redox
(1) Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or
redox reactions
(2) In oxidation, a substance loses electrons,
or is oxidized
(3) In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
(4) Generalized redox reaction
(5) EX. NaCl redox reaction
(6) The electron donor is called the reducing agent
(7) The electron receptor is called the oxidizing agent
(8) Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
(a) An example is the reaction between methane
and O2
d) Oxidation of Organic Fuel Molecules During Cellular Respiration
i) During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced
ii) Organic molecules with an abundance of hydrogen are excellent sources of high-energy electrons
iii) Energy is released as the electrons associated with hydrogen ions are transferred to oxygen, a lower energy
state
e) Stepwise Energy Harvest via NAD

and the Electron Transport Chain
i) In cellular respiration, glucose and other organic molecules are broken down in a series of steps
ii) Electrons from organic compounds are usually first transferred to NAD, a coenzyme
iii) As an electron acceptor, NAD functions as an oxidizing agent during cellular respiration
(1) Each NADH (the reduced form of NAD) represents stored energy that is tapped to synthesize ATP
iv) Dehydrogenase reaction
v) NADH passes the electrons to the electron transport chain
(1) Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of
one explosive reaction
vi) O2 pulls electrons down the chain in an energy-yielding tumble
vii) The energy yielded is used to regenerate ATP
f) The Stages of Cellular Respiration: A Preview
i) Harvesting of energy from glucose has three stages
(1) Glycolysis (breaks down glucose into two molecules of pyruvate)
(2) The citric acid cycle (completes the breakdown of glucose)
(3) Oxidative phosphorylation (accounts for most of the ATP synthesis)
ii) The process that generates almost 90% of the ATP is called oxidative phosphorylation because it is powered
by redox reactions
iii) A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level
phosphorylation
iv) For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of
ATP
v) We can use money as an analogy for cellular respiration:
(1) Glucose is like a larger-denomination bill—it is worth a lot, but it is hard to spend
(2) ATP is like a number of smaller-denomination bills of equivalent value—they can be spent more easily
(3) Cellular respiration cashes in a large denomination of energy (glucose) for the small change of many
molecules of ATP
3) Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
a) Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate
b) Glycolysis occurs in the cytoplasm and has two major phases
i) Energy investment phase
ii) Energy payoff phase
c) Glycolysis occurs whether or not O2 is present
