 Chapter 9: Cellular Respiration: Harvesting Chemical Energy
• Overview: Life Is Work
• Living cells require energy from __________________________
• Some animals, such as the giant panda, obtain energy by eating plants,
and some animals feed on other organisms that eat plants
• Energy flows into an ecosystem as _____________ and leaves as _______
• The chemical elements essential to life are ____________________:
– Photosynthesis generates O2 and organic molecules, which are used
in cellular respiration
– Cells use chemical energy stored in organic molecules to regenerate
ATP, which powers work
 Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
• Several processes are central to cellular respiration and related pathways
• Catabolic Pathways and Production of ATP
– The breakdown of organic molecules is exergonic and they can
therefore act as fuels.
– Two important catabolic pathways are:
• ________________________ is a partial degradation of sugars
that occurs without O
2
• _________________________________ consumes organic
molecules and O and yields ATP
2
– _________________________________ is also a catabolic pathway.
It is similar to aerobic respiration but consumes compounds other
than O
2
– __________________________ includes both aerobic and anaerobic
respiration but is often used to refer to just aerobic respiration
– Although carbohydrates, fats, and proteins are all consumed as fuel,
it is helpful to trace cellular respiration with the sugar glucose:
– How does a catabolic pathway, like this, that decomposes glucose,
yield energy? The answer is based on the transfer of electrons during
the chemical reactions.
• Redox Reactions: Oxidation and Reduction
– The transfer, or relocation, of electrons during chemical reactions
____________________________________________
– This released energy is ultimately used to _____________________
• The exergonic release of energy from glucose is used to
phosphorylate ADP to ATP. Life processes constantly consume
ATP; cellular respiration burns fuels and uses the energy to
regenerate ATP.
• The Principle of Redox
– Chemical reactions that transfer electrons between reactants are
called oxidation-reduction reactions, or _______________________
• In ________________, a substance __________ electrons, or is
oxidized
• In ________________, a substance ___________ electrons, or
is reduced (the amount of positive charge is reduced)
• Specific Example:
• Generalized Redox Reaction:
-
• The electron donor (Xe )is called the _____________________
• The electron receptor (Y) is called the ____________________
– Some redox reactions do not transfer electrons but change the
_________________________________ in covalent bonds
• An example is the reaction between _____________________
• Oxidation of Organic Fuel Molecules During Cellular Respiration
– During cellular respiration, the fuel (such as glucose) is oxidized, and
O2 is reduced:
– The electrons _________________________ along the way, and
energy is released.
+
• Stepwise Energy Harvest via NAD and the Electron Transport Chain
– In cellular respiration, glucose and other organic molecules are
____________________________________; each step catalyzed by
an enzyme:
1. Electrons are stripped from glucose—but they travel with a
proton (i.e. as a ________________________).
2. The hydrogen atoms are not transferred directly to oxygen, but
instead are usually passed to an electron carrier; the coenzyme
__________________________________________
+
o As an electron acceptor, NAD functions as an oxidizing
agent during cellular respiration
o _______________________________ remove a pair of
hydrogen atoms from glucose (2 electrons and 2 protons).
This ______________________. The coenzyme __________
____________________________________. The other
proton is released as a hydrogen ion ________.
3. NADH passes the electrons to the _______________________
o Unlike an uncontrolled reaction, the electron transport chain
passes electrons in a series of steps instead of one explosive
reaction
4. ____ pulls electrons down the chain in an energy-yielding tumble
5. The energy yielded is used to _____________________
• The Stages of Cellular Respiration: A Preview
– Cellular respiration has _________________________:
• __________________ (breaks down glucose into two molecules
of pyruvate)
• ______________________ (completes the breakdown of glucose)
• __________________________________ (accounts for most of
the ATP synthesis)
– The process that generates most of the ATP is called _______________
______________________ because it is _________________________
– Read page 166.
– Oxidative phosphorylation accounts for almost ___________________
generated by cellular respiration
– A smaller amount of ATP is formed in glycolysis and the citric acid cycle
by __________________________________________
 Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to
pyruvate
• ___________________ (“splitting of sugar”) breaks down glucose into
_________________________________
• Glycolysis occurs in the _________________ and has two major phases:
– _______________________________
– _______________________________
SEE HANDOUT #1 FOR DETAILS
• Final Results of Glycolysis
– Overall, glycolysis has _________________ in the energy investment
phase (steps 1 and 3) and _________________ in the energy payoff
phase (steps 7 and 10), for a _____________________.
– Additional energy was stored in __________ ( step 6), which can be
used to make ATP by oxidative phosphorylation if oxygen is present.
– Glucose has been oxidized to ____________________________, the
end product of the glycolytic pathway.
– __________________________, the chemical energy in pyruvate can
be extracted by the citric acid cycle.
– _________________________, fermentation may occur.
 Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of
organic molecules
• Glycolysis release___________________________stored in glucose. Most
of it remains as potential energy stored in the two pyruvate molecules.
• In the presence of O , _______________________________________
2
(Note: in prokaryotic cells this process will occur in the cytosol).
• Before the citric acid cycle can begin, pyruvate must be converted to
___________________, which links the cycle to glycolysis
• The _____________________, also called the ________________, takes
place within the ___________________________
– The cycle oxidizes organic fuel derived from pyruvate, generating
______________________________________________
– The citric acid cycle has ________________, each catalyzed by a
specific enzyme
– The acetyl group of acetyl CoA joins the cycle by combining with
_____________________, forming ________________
– The next seven steps _____________________________________,
making the process a _______________
– The NADH and FADH produced by the cycle relay electrons
2
extracted from food to the ______________________________
**SEE HANDOUT #2 FOR DETAILS
 Concept 9.4: During oxidative phosphorylation, chemiosmosis couples
electron transport to ATP synthesis
• Following glycolysis and the citric acid cycle, ______________________
account for most of the energy extracted from food
• These two electron carriers donate electrons to the electron transport
chain, which powers ATP synthesis via _____________________________
• The Pathway of Electron Transport
– The electron transport chain is in the __________ of the
mitochondrion
– Most of the chain’s components are _____________, which exist in
multiprotein complexes
– The carriers alternate reduced and oxidized states as they
________________________________________
– Electrons drop in free energy as they go down the chain and are
_______________________, forming ___________
– Electrons are transferred from NADH or FADH to the electron
2
transport chain
– Electrons are passed through a number of proteins including
____________________ (each with an iron atom) to O
2
– The electron transport chain _____________________
– The chain’s function is to break the large free-energy drop from food
to O into smaller steps that _________________________________
2
***SEE HANDOUT #3 FOR DETAILS
• Chemiosmosis: The Energy-Coupling Mechanism
– Electron transfer in the electron transport chain causes proteins to
___________ from the mitochondrial matrix to the intermembrane
space
+
– H then moves back across the membrane, passing through channels
in ____________________________
+
– ATP synthase uses the exergonic flow of H to drive phosphorylation
of ATP
– This is an example of _____________________, the use of ________
__________________________________________________
+
– The energy stored in a H gradient across a membrane couples the
redox reactions of the electron transport chain to ATP synthesis
+
– The H gradient is referred to as a __________________________,
emphasizing its capacity to do work
– It is in place because the inner membrane of the mitochondria is
impermeable to hydrogen ions. They are like water behind a dam—
with their only exit being ATP synthase.
• An Accounting of ATP Production by Cellular Respiration
– During cellular respiration, most energy flows in this sequence:
– About ______ of the energy in a glucose molecule is transferred to
ATP during cellular respiration, making about __________
 Concept 9.5: Fermentation and anaerobic respiration enable cells to
produce ATP without the use of oxygen
• Most cellular respiration ________________ to produce ATP
• Without electronegative oxygen to pull electrons down the ETC, oxidative
phosphorylation ceases.
• Glycolysis can produce ATP __________________ O (in aerobic or
2
anaerobic conditions)
• In the absence of O , glycolysis couples with ________________________
2
___________________ to produce ATP
– ______________________ uses an ___________________________
with an electron acceptor other than O , for example ____________
2
• It takes place in some prokaryotic cells that live in
environments without oxygen.
• Hydrogen sulfide (H S) is produced as a by-product instead of
2
water.
– ____________________ uses ________________________ instead
of an electron transport chain to generate ATP
• Types of Fermentation
– Fermentation consists of ___________________________________
________ which can be reused by glycolysis
– Two common types are _________________________ and
___________________________________
• In ____________________________, pyruvate is converted to
_____________ in two steps, with the first ________________
o Alcohol fermentation by _________ is used in _________
____________________________
***SEE HANDOUT #4 FOR DETAILS
• In ____________________________, pyruvate is reduced to
NADH, forming ____________ as an end product, with no
release of ___________
o Lactic acid fermentation by some fungi and bacteria is
used to make _____________________
o ______________________ use lactic acid fermentation to
generate ATP when O is scarce
2
***SEE HANDOUT #4 FOR DETAILS
• Fermentation and Aerobic Respiration Compared
– Both processes use ____________________________________ and
other organic fuels to pyruvate
– The processes have ______________________________________:
an organic molecule (such as pyruvate or acetaldehyde) in
fermentation and O in cellular respiration
2
– Cellular respiration produces __________ per glucose molecule;
fermentation produces ____________ per glucose molecule
– ________________________carry out fermentation or anaerobic
respiration and cannot survive in the presence of O
2
– Yeast and many bacteria are __________________________,
meaning that they can survive using either fermentation or cellular
respiration
• In a facultative anaerobe, pyruvate is a fork in the metabolic
road that leads to two alternative catabolic routes
• The Evolutionary Significance of Glycolysis
– Glycolysis occurs in ________________________
– Glycolysis probably evolved in _______________________________
_____________________________
 Concept 9.6: Glycolysis and the citric acid cycle connect to many other
metabolic pathways
• Gycolysis and the citric acid cycle are major intersections to various
____________________________________
• The Versatility of Catabolism
– Catabolic pathways ___________________
______________________ into cellular
respiration
– Glycolysis accepts a wide range of
____________________
– Proteins must be
_________________________; amino groups
can feed glycolysis or the citric acid cycle
– Fats are digested to ___________ (used in
glycolysis) and ________________ (used in
generating acetyl CoA)
– Fatty acids are broken down by
_____________ and yield acetyl CoA
– An oxidized gram of fat produces _________________________ as
much ATP as an oxidized gram of carbohydrate
• Biosynthesis (Anabolic Pathways)
– The body uses small molecules to build other substances
– These small molecules may come directly from food, from glycolysis,
or from the citric acid cycle
• Regulation of Cellular Respiration via Feedback Mechanisms
– ____________________ is the most common mechanism for control
– If ATP concentration begins to drop, respiration speeds up; when
there is plenty of ATP, respiration slows down
– Control of catabolism is based mainly on ______________________
___________________ at strategic points in the catabolic pathway
You should now be able to:
1. Explain in general terms how redox reactions are involved in energy exchanges
2. Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it
occurs and the products that result
3. In general terms, explain the role of the electron transport chain in cellular respiration
4. Explain where and how the respiratory electron transport chain creates a proton gradient
5. Distinguish between fermentation and anaerobic respiration
6. Distinguish between obligate and facultative anaerobes