Cellular
Respiration
Chapter 9: Cellular Respiration
Cellular Respiration
Living cells require energy from
outside sources
Organisms use
as their main energy source
Cellular respiration is the
process of breaking down food
molecules to
Energy is released in the process of
respiration when the cells of plants
and animals convert sugar and
oxygen into carbon dioxide and
water
Respiration
 The breakdown of organic
molecules is

respiration
consumes organic molecules
and O2 and yields ATP
(oxygen required)

respiration
is similar to aerobic
respiration but consumes
compounds other than O2
(no oxygen required)

is a partial
degradation of sugars that
occurs without O2
Cellular Respiration
 Cellular respiration includes both aerobic
and anaerobic respiration but is often used to
refer to aerobic respiration
 Although carbohydrates, fats, and proteins
are all consumed as fuel, it is helpful to trace
cellular respiration with the sugar glucose:
Redox Reactions
 The transfer of electrons during chemical reactions
releases energy stored in organic molecules
 This released energy is used to make ATP
 Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions, or
 In oxidation, a substance
, or is
oxidized
 In reduction, a substance
, or is
reduced (the amount of positive charge is reduced)
 In cellular respiration, the glucose is
and
O2 is
NAD+
 In cellular respiration, glucose and
other organic molecules are broken
down in a series of steps
 Electrons from organic compounds
are usually first transferred to
NAD+ (nicotinamide adenine
dinucleotide), a coenzyme
 As an electron acceptor, NAD+
functions as an
 Each NADH (the reduced form
of NAD+) represents stored
energy that is tapped to
synthesize ATP
 NADH passes the electrons to
the
Electron Transport Chain
 Unlike an uncontrolled
reaction, the electron
transport chain passes
electrons in a series of
steps instead of one
explosive reaction

pulls
electrons down the
chain in an energyyielding tumble
 The energy yielded is
used to regenerate
Stages of Cellular Respiration
1)
- Anaerobic (breaks down
glucose into two molecules of pyruvate)
2)
- Aerobic (Kreb’s Cycle completes the breakdown of glucose)
3)
- Aerobic (ETC accounts for most of the ATP synthesis)
Mitochondria
1) Glycolysis

2) Citric Acid Cycle

3) Oxidative
Phosphorylation (ETC)

QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Step 1: Glycolysis

 Breaks down glucose
(C6H12O6) into two
molecules of pyruvic acid
- AKA
 Anaerobic
 Occurs in the cytoplasm
 NAD picks up H+ and
electrons to form NADH2
Glycolysis Summary
Location:
Products
Reactants







Simple Summary
Summary total
Bridge Reaction
 In the presence of O2, pyruvate enters the mitochondrion
 Before the citric acid cycle can begin, pyruvate must be
converted to
, which links the cycle to glycolysis
 In the mitochondria matrix…
1) Pyruvic Acid loses a C to form acetic acid (2-C)
2) The lost carbon binds with O2 making CO2
3)Acetic acid binds with Coenzyme-A forming Acetyl Co-A
Step 2: The Kreb’s Cycle
(Citric Acid Cycle)
 Takes place within the mitochondrial
matrix
 There are
, each
catalyzed by a specific enzyme
 The acetyl group of acetyl CoA joins
the cycle by combining with
(4-C molecule),
forming a 6-C molecule known as
 The next seven steps decompose the
citrate back to oxaloacetate, making
the process a cycle
Step 2: The Kreb’s Cycle
(Citric Acid Cycle)
 2 molecules of CO2 are released

(flavin adenine dinucleotide another ion carrier) pick up electrons and H+ becoming
NADH and FADH2
 The NADH and FADH2 produced by the cycle relay
electrons extracted from food to the electron transport
chain
 The cycle generates 1 ATP, 3 NADH, and 1 FADH2 per
turn
 Recall that
glycolysis resulting in
for each glucose molecule!
are formed during
of the Kreb’s cycle
Kreb’s Cycle Summary
Location:
Reactants

Products




Kreb’s Summary
Kreb's Summary 2
Step 3: Electron Transport Chain
(ETC)
 Aerobic process
 Requires
as the
final electron acceptor
 Takes place in the cristae of
the mitochondria
 A series of molecules that
excited electrons pass along,
to release energy as ATP
 Most of the chain’s
components are
,
which exist in multiprotein
complexes
Step 3: Electron Transport Chain
(ETC)
 Following glycolysis and the citric acid cycle,
NADH and FADH2 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 carriers alternate
as they accept and donate electrons
 Electrons drop in free energy as they go down the
chain
 They are finally passed to O2
forming
NADH and FADH2
 Dump the electrons and protons they’ve gathered
throughout glycolysis and the citric acid cycle
 Again,
 O2 + 2e- + 2H+  H2O
 Electrons are passed through a number of proteins
including cytochromes (each with an iron atom) to O2
 The chain’s function is to break the large free-energy drop
from food to O2 into smaller steps that release energy in
manageable amounts

to generate large amounts of ATP
Chemiosmosis
 Electron transfer in the ETC causes
proteins to pump
from the
mitochondrial matrix to the
intermembrane space
 H+ then moves back across the
membrane, passing through
channels in
(enzyme that acts like an ion pump)
 ATP synthase uses the exergonic
flow of H+ to drive phosphorylation
of ADP
 This is an example of
chemiosmosis, the use of energy
in a H+ gradient to drive cellular
work
 The H+ gradient is called the
ETC Summary
ETC
ETC Summary
Location:
Reactants


Product



Simpler ETC Summary
Best ETC Summary
Whole Respiration Process
Total Energy
Total ATP from 1 molecule of glucose in
Stage
Glycolysis
ATP
+ 4 Total
(b/c 2 are used in the first step)
CA Cycle
ETC
_________________
TOTAL
During cellular respiration, most energy flows in this sequence:
Glucose -> NADH -> electron transport chain -> proton-motive
force -> ATP
Fermentation
 Most cellular respiration requires O2 to produce
ATP
 Glycolysis can produce ATP
(in aerobic or anaerobic conditions)
 In the absence of O2, glycolysis couples with
fermentation or anaerobic respiration to produce
ATP
 Fermentation uses
instead of an
electron transport chain to generate ATP
 2 Types:

Fermentation

Fermentation
Lactic Acid Fermentation
 In lactic acid
fermentation,
,
forming lactate as an end
product, with no release
of CO2
 Lactic acid fermentation
by some fungi and
bacteria is used to make
 Human muscle cells use
lactic acid fermentation to
generate ATP when O2 is
scarce
Lactic Acid Fermentation
 Example: Burning
feeling in muscles
during a workout
• From oxygen debt
•
• Lactate
Alcohol Fermentation
 In alcohol
fermentation,
pyruvate is converted
to
(type
of alcohol) in two
steps, with the first
releasing CO2
 Bacteria and fungi
(yeast)
 Alcohol fermentation
by yeast is used in
Fermentation
 Obligate anaerobes
carry out fermentation
or anaerobic respiration
and
 Yeast and many
bacteria are
facultative
anaerobes, meaning
that they can survive
using either
fermentation or cellular
respiration
Review
Role of Macromolecules
 Catabolic pathways funnel electrons from many kinds
of organic molecules into cellular respiration
 Glycolysis accepts a wide range of
 Proteins must be digested to amino acids
 Amino groups can feed
 Fats are digested to glycerol (used in glycolysis) and
fatty acids (used in generating acetyl CoA)
 Fatty acids are broken down by beta oxidation and
yield
 An oxidized gram of fat produces more than twice as
much ATP as an oxidized gram of carbohydrate
Regulation of Cell Respiration
 Feedback inhibition is the
most common mechanism
for control
 If ATP concentration begins
to drop, respiration
 When there is plenty of ATP,
respiration
 Control of catabolism is
based mainly on regulating
the activity of enzymes at
strategic points in the
catabolic pathway
Review Questions
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Define cellular respiration and state its importance as a life process.
Differentiate between aerobic respiration, anaerobic respiration, and
fermentation.
State and explain the chemical equation for cellular respiration.
Define oxidation and reduction and explain the idea of redox reactions.
Explain the use of NAD+ as a coenzyme.
Explain the electron transport chain (ETC).
Name the 3 major stages of cell respiration, along with their locations.
Explain glycolysis, stating the reactants, products, and major activities.
Explain the bridge reaction, stating the reactants, products, and major activities.
Explain the Kreb’s cycle, stating the reactants, products, and major activities.
Explain glycolysis, stating the reactants, products, and major activities.
Explain the ETC, stating the reactants, products, and major activities.
Explain the role of oxygen in the ETC.
Define chemiosmosis and explain its role in cellular respiration.
Differentiate between lactic acid fermentation and alcohol fermentation.
Differentiate between oblicate anaerobes and facultative anaerobes.
Explain the role of macromolecules in cellular respiration.
Explain how cell respiration is regulated.