Chapter 9
Cellular
Respiration:
Harvesting
Chemical Energy
1
Respiration Facts:
All the energy in all
the food you eat can
be traced back to
sunlight
If you exercise too
hard, your muscles
shut down from a lack
of oxygen
2
FEELING THE “BURN”
When you exercise:
Muscles need energy in order to
perform work
Your cells use oxygen to release
energy from the sugar glucose
Both aerobic and anaerobic
burning of glucose can take
place in your cells
3
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
4
Anaerobic Metabolism
Without enough oxygen,
muscle cells break down
glucose to produce lactic acid
Lactic acid is associated with
the “burn” associated with
heavy exercise
If too much lactic acid builds
up, your muscles give out
5
Physical Conditioning
Allows your body to
adapt to increased
activity
The body can increase
its ability to deliver
oxygen to muscles
Long-distance runners
wait until the final
sprint to exceed their
aerobic capacity
6
Why Photosynthesis?
Only producers are capable of
Photosynthesis
Light energy from the sun powers
this chemical process that makes
organic molecules (sugars)
This process occurs in the
mesophyll cells of leaves of
producers (plants & algae)
7
ENERGY FLOW IN THE BIOSPHERE
Energy stored in food can be traced
back to the sun
Fuel molecules in food store solar
energy in chemical bonds
Animals depend on plants to convert
solar energy to chemical energy
This chemical energy is in the form
of sugars and other organic molecules
8
Autotrophs & Heterotrophs
Autotrophs - Plants and other
organisms that make all their own
organic matter from inorganic
nutrients
Heterotrophs - Humans and other
animals that cannot make organic
molecules from inorganic ones
9
The Cycle of Energy
Producers Biologists refer to
plants and other
autotrophs as the
producers in an
ecosystem
Consumers Heterotrophs are
consumers, because
they eat plants or
other animals
10
Chemical Cycling
The ingredients for photosynthesis are
carbon dioxide and water
CO2 is obtained from the air by a plant’s
leaves
H2O is obtained from the damp soil by a
plant’s roots
Chloroplasts rearrange the atoms of these
ingredients to produce sugars (glucose) and
other organic molecules
Oxygen gas is a by-product of
photosynthesis
11
Chemical Cycling
Both plants and animals perform
cellular respiration
Cellular respiration is a chemical
process that harvests energy
from organic molecules and occurs
in the mitochondria
The waste products of cellular
respiration, CO2 and H2O, are
used in photosynthesis
12
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
13
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
14
The Versatility of Cellular
Respiration
Cellular respiration can “burn”
other kinds of molecules besides
glucose:
Diverse types of carbohydrates
Fats
Proteins
15
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
16
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
17
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
18
Breathing
Lungs
Muscle
cells
Cellular
Respiration
19
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
20
Redox Reactions
Chemical reactions that transfer
electrons from one substance to
another are called oxidationreduction reactions
REDOX short for oxidationreduction reactions
21
Redox Reactions
The loss of electrons during a
redox reaction is called
oxidation
The acceptance of electrons
during a redox reaction is called
reduction
Reducing agent:
Oxidizing agent:
e- donor
e- acceptor
22
REDOX in Cellular Respiration
Glucose loses electrons (and hydrogens)
Oxidation
Glucose
Oxygen
Carbon
dioxide
Water
Reduction
Oxygen gains electrons (and hydrogens)]
23
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
24
The Metabolic Pathway of
Cellular Respiration
Cellular respiration is an example
of a metabolic pathway
A series of chemical reactions in
cells either building or breaking
down molecules
25
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
26
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
27
Glycolysis
Stage One
28
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
29
Glycolysis
METABOLIC PATHWAY
2 Pyruvic acid
Glucose
30
Glycolysis
CoA
Acetic
acid
Pyruvic
acid
CO2
Coenzyme A
Acetyl-CoA
(acetyl-coenzyme A)
31
Glycolysis Summary
The Krebs cycle extracts the
energy of sugar by breaking the
acetic acid molecules all the way
down to CO2
The cycle uses some of this energy
to make ATP
The cycle also forms NADH and
FADH2 ( 2 energy carrier molecules)
32
Krebs Cycle
Stage Two
33
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
34
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
37
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
38
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)
39
Protein
complex
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Electron transport chain
ATP synthase
40
Food
Polysaccharides
Sugars
Glycerol
Fats
Fatty acids
Proteins
Amino acids
Amino groups
Glycolysis
AcetylCoA
Krebs
Cycle
Electron
Transport
41
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
426.14
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
43
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
44
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
45
2 ADP+ 2
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Lactic
acid
Lactic acid fermentation
46
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
48
The food industry uses yeast to
produce various food products
49
Related metabolic processes
Fermentation:
alcohol~
pyruvate to ethanol
lactic acid~
pyruvate to lactate
Facultative
anaerobes
(yeast/bacteria)
Beta-oxidation
lipid catabolism
50
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
51
52