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Chapter 8
Cellular
Respiration:
Harvesting
Chemical Energy
1
Aerobic & Anaerobic Metabolism
Aerobic metabolism
- When enough oxygen reaches
cells to support energy needs
- Maximum energy production
Anaerobic metabolism
– When the demand for oxygen
outstrips the body’s ability to
deliver it
– Low energy production
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AEROBIC HARVEST OF FOOD
ENERGY
Cellular respiration is the main
way that chemical energy is
harvested from food and
converted to ATP for cellular
work
Cellular respiration is an aerobic
process requiring oxygen
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The Versatility of Cellular
Respiration
Cellular respiration can “burn”
other kinds of molecules besides
glucose:
Diverse types of carbohydrates
Fats
Proteins
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The Overall Equation for
Cellular Respiration
A common fuel molecule for
cellular respiration is glucose
This is the overall equation for
what happens to glucose during
cellular respiration
Glucose
Oxygen
Carbon dioxide
Water
Energy
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But Remember …
Cellular Respiration is a metabolic
pathway, not a single reaction
Many chemical reactions, both
aerobic and anaerobic, are
involved in the process of cellular
respiration
Lots of enzymes are required for
the process to occur
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The Relationship Between Cellular
Respiration and Breathing
Cellular respiration and breathing
are closely related
Cellular respiration requires a
cell to exchange gases with its
surroundings
Breathing exchanges these gases
between the blood and outside
air
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The Role of Oxygen in Cellular
Respiration
During cellular respiration,
hydrogen and its bonding
electrons change partners
Hydrogen and its electrons go
from sugar to oxygen, forming
water
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Comparison
Respiration
Photosynthesis
Occurs in all
organisms
Occurs in only
chlorophyll containing
organisms
Breaks down glucose Stores light energy as
chemical energy in the
bonds of glucose
Releases carbon
Produces glucose and
dioxide, water, & ATP
oxygen
Exergonic Reaction
Endergonic reaction
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The Metabolic Pathway of Cellular
Respiration
All of the reactions involved in
cellular respiration can be grouped
into three main stages
Glycolysis – occurs in cytoplasm
The Krebs cycle – occurs in matrix
of mitochondria
Electron transport – occurs across
the mitochondrial membrane
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A Road Map for Cellular Respiration
Mitochondrion
Cytosol
High-energy
electrons
carried
mainly by
NADH
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
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Glycolysis
Stage One
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Stage 1: Glycolysis
Glycolysis takes place in the
cytoplasm
Oxygen NOT required
Process breaks a six-carbon glucose
into two, three-carbon molecules
A molecule of glucose is split into two
molecules of pyruvic acid
These molecules then donate high
energy electrons to NAD+, forming
NADH
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Glycolysis
METABOLIC PATHWAY
2 Pyruvic acid
Glucose
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Glycolysis
CoA
Acetic
acid
Pyruvic
acid
CO2
Coenzyme A
Acetyl-CoA
(acetyl-coenzyme A)
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Krebs Cycle
Stage Two
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Stage 2: The Krebs Cycle
The Krebs cycle completes the
breakdown of sugar
It occurs inside the mitochondria
In the Krebs cycle, pyruvic acid
from glycolysis is first “prepped”
into a usable form by combining
it with enzyme Co-A to make
Acetyl-CoA
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ACETYL Co-A
Input
Output
2
1 Acetic acid
2 CO2
3
ADP
Krebs
Cycle
3 NAD
4
FAD
5
6
Electron Transport
Stage 3
Stage 3: Electron Transport
Electron transport releases the
energy your cells need to make
the most of their ATP
The molecules of electron
transport chains are built into
the inner membranes of
mitochondria
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Stage 3: Electron Transport
The chain functions as a chemical
machine that uses energy
released by the “fall” of
electrons to pump hydrogen ions
across the inner mitochondrial
membrane
These ions store potential energy
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Electron transport chain
Cytochromes carry electron
carrier molecules (NADH &
FADH2) down to oxygen
Chemiosmosis:
energy coupling mechanism
ATP synthase:
produces ATP by using the H+
gradient (proton-motive force)
pumped into the inner membrane
space from the electron
transport chain; this enzyme
harnesses the flow of H+ back
into the matrix to phosphorylate
ADP to ATP (oxidative
phosphorylation)
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Protein
complex
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Electron transport chain
ATP synthase
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Food
Polysaccharides
Sugars
Glycerol
Fats
Fatty acids
Proteins
Amino acids
Amino groups
Glycolysis
AcetylCoA
Krebs
Cycle
Electron
Transport
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Adding Up the ATP
Cytosol
Mitochondrion
Glycolysis
Glucose
2
Pyruvic
acid
2
AcetylCoA
Krebs
Cycle
Electron
Transport
Maximum
per
glucose:
by direct
synthesis
by
direct
synthesis
by
ATP
synthase
Figure
256.14
FERMENTATION: ANAEROBIC
HARVEST OF FOOD ENERGY
Some of your cells can actually work
for short periods without oxygen
(anaerobic respiration)
For example, muscle cells can produce
ATP under anaerobic conditions
Called Fermentation
Involves The anaerobic harvest of
food energy
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Fermentation in Human Muscle
Cells
Human muscle cells can make ATP with
and without oxygen
They have enough ATP to support
activities such as quick sprinting for
about 5 seconds
A secondary supply of energy (creatine
phosphate) can keep muscle cells going
for another 10 seconds
To keep running, your muscles must
generate ATP by the anaerobic process
of fermentation
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Glycolysis is the metabolic
pathway that provides ATP during
fermentation
Pyruvic acid is reduced by NADH,
producing NAD+, which keeps
glycolysis going
In human muscle cells, lactic acid
is a by-product
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2 ADP+ 2
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Lactic
acid
Lactic acid fermentation
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Fermentation in Microorganisms
Various types of microorganisms
perform fermentation
Yeast cells carry out a slightly
different type of fermentation
pathway
This pathway produces CO2 and
ethyl alcohol
2 ADP+ 2
2 CO2 released
2 ATP
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Ethyl
alcohol
Alcoholic fermentation
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The food industry uses yeast to
produce various food products
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Related metabolic processes
Fermentation:
alcohol~
pyruvate to ethanol
lactic acid~
pyruvate to lactate
Facultative
anaerobes
(yeast/bacteria)
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Review: Cellular Respiration
Glycolysis:
– 2 ATP (substrate-level phosphorylation)
Kreb’s Cycle:
– 2 ATP (substrate-level phosphorylation)
Electron transport & oxidative
phosphorylation:
– 2 NADH (glycolysis) = 6ATP
– 2 NADH (acetyl CoA) = 6ATP
– 6 NADH (Kreb’s) = 18 ATP
– 2 FADH2 (Kreb’s) = 4 ATP
38 TOTAL ATP/glucose
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Sunlight supplies the energy!
Sunlight
energy
Ecosystem
Raw materials for
cellular
respiration
Bonds of Glucose, made in
chloroplasts, contain the
stored energy
Photosynthesis
(in chloroplasts)
Glucose
Oxygen
Carbon dioxide
Water
Cellular respiration
(in mitochondria)
Raw materials for
photosynthesis
Glucose broken down
to release energy for
cellular work
Cellular energy
Heat energy
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