Chapter 9
Cellular
Respiration:
Harvesting
Chemical
Energy
Principles of Energy Harvest
Photosynthesis
vs.
Cellular respiration
Principles of Energy Harvest
Photosynthesis
Cellular respiration
Endergonic
Exergonic
Products: O2,
C6H12O6
Products: CO2,
H2O, ENERGY
Reactants: CO2,
H2O, ENERGY
Reactants: O2,
C6H12O6
Chloroplasts
Mitochondria
Principles of Energy Harvest
Cell respiration is catabolic
• Breaks down glucose
Photosynthesis is anabolic
• Synthesizes glucose
Redox reactions
Oxidation - Reduction
• Oxidation is e- or H
loss
• Reduction is e- or H
gain
• Reducing agent:
e- donor
• Oxidizing agent:
e- acceptor
Oxidizing agent in respiration
• NAD+ (nicotinamide
adenine dinucleotide)
• Removes electrons
from food (series of
reactions)
• NAD+ is reduced to
NADH
• Enzyme action:
dehydrogenase
• Oxygen is the eventual
e- acceptor
Electron transport chains
• Electron carrier molecules
(membrane proteins)
• Shuttles electrons that
release energy used to
make ATP
• Sequence of reactions that
prevents energy release in
1 explosive step
• Electron route:
food---> NADH --->
electron transport chain --->
oxygen
Cellular respiration summary
• Glycolysis: cytosol;
degrades glucose into
pyruvate
• Kreb’s Cycle:
mitochondrial matrix;
pyruvate into carbon
dioxide
• Electron Transport
Chain: inner membrane
of mitochondrion;
electrons passed to
oxygen
Glycolysis
1 Glucose ---> 2 pyruvate molecules
• The First Stage of Respiration for
ALL living organisms, anaerobes or
aerobes, is called Glycolysis
and takes place in the Cytosol.
Net Result
•
•
•
•
2 Pyruvic Acid
2 ATP per glucose (4 – 2 = 2)
2 NADH
In summary, glycolysis takes one
glucose and turns it into 2 pyruvates
(molecules of pyruvic acid), 2 NADH
and a net of 2 ATP.
Glycolysis
4 ATP’s are
produced
Pyruvic Acid (3 Carbons)
Glucose
(6 carbons)
2 ATP’s supply
the activation
energy
2 NAD+ + 2 e-
Pyruvic Acid (3 Carbons)
2 NADH
4 ATP Yield = 2 ATP Net Gain
Glycolysis
1 Glucose ---> 2 pyruvate molecules
• Energy investment phase: cell
uses ATP to phosphorylate fuel
• Energy payoff phase: ATP is
produced by substrate-level
phosphorylation and NAD+ is
reduced to NADH by food
oxidation
• Net energy yield per glucose
molecule: 2 ATP plus 2 NADH;
no CO2 is released; occurs
aerobically or anaerobically
(no O2 used)
Mitochondrion
In order for Aerobic
Respiration to continue
the Pyruvic acid is first
converted to Acetic Acid
by losing a carbon atom
and 2 oxygens as CO2.
The Acetic acid then must
enter the matrix region of
the mitochondria. The
CO2 produced is the CO2
animals exhale when they
breathe.
The Krebs Cycle
(AKA the Citric Acid Cycle, Tricarboxylic Acid Cycle)
Sir Hans Adolf
Krebs
Produces most of
the cell's energy in
the form of NADH
and FADH2… not
ATP
Does NOT require O2
Kreb’s Cycle
Creates NADH + FADH2 + ATP
Each pyruvate is converted
into acetyl CoA (x 2):
CO2 is released
NAD+ ---> NADH
coenzyme A (from B
vitamin), makes
molecule very reactive
• From this point, each
turn 2 C atoms enter
(pyruvate) and 2 exit
(carbon dioxide)
Kreb’s Cycle
Requires O2, creates NADH + FADH2 + ATP
• “The cycle”:
• Oxaloacetate is
regenerated
For each pyruvate that enters
(x2):
• 3 NAD+ reduced to NADH
• 1 FAD+ reduced to FADH2
(riboflavin, B vitamin)
• 1 ATP molecule
Krebs cycle Summary
Occurs in matrix of mitochondrion
As a result of one turn of the Krebs cycle the
cell makes:
1 FADH2
3 NADH
1 ATP
However, each glucose produces two pyruvic
acid molecules…. So the total outcome is:
2 FADH2
6 NADH
2 ATP
Oxidative Phosphorylation
Occurs in inner mitochondrial membrane
Only phase that requires O2
Requires
NADH or FADH2
ADP and P
O2
Electron transport chain
http://vcell.ndsu.nodak.edu/animations/etc/movie.htm
The Chemiosmotic Hypothesis
• proposes that the Electron Transport
Chain energy is used to move H+
(protons) across the cristae membrane,
and
• that ATP is generated as the H+ diffuse
back into the matrix through ATP
Synthase.
Electron transport chain
Cytochromes carry electron carrier molecules
(NADH & FADH2) down to oxygen
Chemiosmosis:
energy coupling mechanism
ATP synthase (enzyme):
produces ATP using H+
gradient (proton-motive
force) pumped into the inner
membrane space from the
electron transport chain
harnesses the flow of H+ back
into the matrix to
phosphorylate ADP to ATP
(oxidative phosphorylation)
Review: Cellular Respiration
38 molecules ATP/glucose molecule (theoretically!)
1. Glycolysis:
2 ATP (substrate-level
phosphorylation)
2. Kreb’s Cycle:
2 ATP (substrate-level
phosphorylation)
3. Electron transport &
oxidative phosphorylation:
2 NADH (glycolysis) = 6ATP
4. 2 NADH (acetyl CoA) = 6ATP
6 NADH (Kreb’s) = 18 ATP
2 FADH2 (Kreb’s) = 4 ATP
• 38 TOTAL ATP/glucose
How other nutrients enter the
catabolic pathway
Control of Glucose Catabolism
But…
Theoretical ATP
Yield of Aerobic
Respiration
Usually Said to
be 36 ATP
Why can’t we agree?
Related metabolic processes
Fermentation:
1. Alcohol: pyruvate to
ethanol
2. Lactic acid: pyruvate
to lactate
•
•
Facultative
anaerobes
(yeast/bacteria)
Beta-oxidation
lipid catabolism
Two Types of Cellular Respiration
• There are two types of Respiration:
Anaerobic Respiration and Aerobic
Respiration
• Some organisms use the Anaerobic
Respiration pathway, and some
organisms use the Aerobic Respiration
pathway.
Anaerobic Respiration:
Alcoholic Fermentation
is carried out by yeast,
a kind of fungus.
Alcoholic Fermentation
(Ethyl Alcohol
or Ethanol)
C6H12O6
2 C2H5OH + 2 CO2
As a result of Alcoholic
Fermentation,
Glucose is converted into 2
molecules of Ethyl Alcohol and 2
Molecules of Carbon Dioxide.
Alcoholic Fermentation
Glycolysis
Released into the environment
4 ATP’s are
produced
CO2
(C2H5OH)
Ethyl Alcohol (2C)
Pyruvic Acid (3C)
Released into the environment
Glucose
(6 carbons)
2 ATP’s supply the
activation energy
2 NAD+ + 2 e-
CO2
Pyruvic Acid (3C)
2 NADH
Ethyl Alcohol (2C)
(C2H5OH)
2 NAD+ + 2 e-
4 ATP Yield = 2 ATP Net Gain
Anaerobic Respiration:
Lactic Acid Fermentation
•
•
•
•
•
Occurs in animals
Uses only Glycolysis.
Does NOT require O2
Produces ATP when O2 is not available.
Carried out by human muscle cells under
oxygen debt.
• Lactic Acid is a toxin and causes fatigue,
soreness and stiffness in muscles.
• Diffuses into blood, detoxified by liver.
Lactic Acid Fermentation
Glycolysis
4 ATP’s are
produced
Pyruvic Acid (3C)
Lactic Acid (3C)
Pyruvic Acid (3C)
Lactic Acid (3C)
Glucose
(6 carbons)
2 ATP’s supply the
activation energy
2 NAD+ + 2 e-
2 NADH
2 NAD+ + 2 e-
4 ATP Yield = 2 ATP Net Gain