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AEROBIC CELLULAR
RESPIRATION
SBI4U
BY SARA AVENT
AGENDA
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Overview
Lab investigations
Redox reactions and free energy
Glycolysis
Pyruvate Oxidation
The Krebs Cycle
Electron Transport and Chemiosmosis
Oxidative ATP Synthesis
Energy efficiency
CURRICULUM EXPECTATIONS
Overall Expectations
• C2. investigate the products of metabolic processes such as
cellular respiration and photosynthesis;
• C3. demonstrate an understanding of the chemical
changes and energy conversions that occur in metabolic
processes.
Specific Expectations
• C2.1: use appropriate terminology related to metabolism,
including, but not limited to: energy carriers, glycolysis,
Krebs cycle, electron transport chain, ATP synthase,
oxidative phosphorylation, chemiosmosis, proton pump.
• C2.2: conduct a laboratory investigation into the process of
cellular respiration to identify the products of the process,
interpret the qualitative observations, and display them in
an appropriate format.
CURRICULUM EXPECTATIONS (CONT’D)
• C3.1: explain the chemical changes and energy
conversions associated with the processes of aerobic
and anaerobic cellular respiration (e.g., in aerobic
cellular respiration, glucose and oxygen react to
produce carbon dioxide, water, and energy in the form
of heat and ATP).
• C3.4: describe, compare, and illustrate (e.g., using flow
charts) the matter and energy transformations that
occur during the processes of cellular respiration
(aerobic and anaerobic) and photosynthesis, including
the roles of oxygen and organelles such as mitochondria
and chloroplasts.
INVESTIGATION
• Using Pasco CO2 gas sensor
students can observe real-time
evidence germinating seeds are
engaged in cellular respiration.
• CO2 gas increases inside the flask
with germinating seeds – proof
that cellular respiration is
occurring as the seeds
germinate.
AEROBIC CELLULAR RESPIRATION
OVERVIEW
• All organisms (except chemoautotrophs) use
glucose as a primary source of energy.
• Through a series of enzyme-controlled redox
reactions, the bonds are broken, and the
molecule is rearranged into more stable
configurations, and energy is released.
oxidized
C6H12O6 (aq) + 6O2(g)  6CO2 (g) + 6H2O (l) + heat + ATP
reduced
REDOX REACTIONS AND ENERGY
C6H12O6 (aq) + 6O2(g)  6CO2 (g) + 6H2O (l) + heat + ATP
Is this oxidation or reduction?
C
H
More ordered
O
H
Less ordered
WHAT ABOUT THE REST?
C6H12O6 (aq) + 6O2(g)  6CO2 (g) + 6H2O (l) + heat + ATP
Is this oxidation or reduction?
O
O
More ordered
O
C
Less ordered
Release of
Free Energy!
VISUALISING ENERGY
http://www.youtube.com/watch?v=6YWGnfnEmgM
REDOX REACTIONS AND NICOTINAMIDE
ADENINE DINUCLEOTIDE
ENERGY TRANSFER
• The ultimate goal of cellular respiration is to capture
as much of the available free energy in the form of
ATP.
• Substrate-level phosphorylation:
HOW MUCH ENERGY IS RELEASED?
• ΔG = -2870 kJ/mol
glucose
• When glucose is burned
in a test tube CO2, H2O
are formed and heat
and light are given off.
• Cells have evolved
methods to trap this
energy (ATP) to power
endergonic processes in
cell.
IN A LIVING CELL THINGS GET
COMPLICATED
• Oxygen won’t just bump into
glucose and react in the
environment.
• What would happen if it
could?
• Solution: activation energy
• How does a cell control this
process?
• Enzymes catalyze and control.
CELLULAR RESPIRATION PROCESS
Stage 4
Stage 1
Stage 2
Stage 3
STAGE 1: GLYCOLYSIS
• 6-carbon glucose  two 3-carbon pyruvates
• Glyco = “sugar”; lysis = “split”
• Cytoplasm
• This is a
complicated
process, but
don’t worry –
students only
need to identify
and understand
the important
parts.
• So what’s
important?
• The points in
the pathway
where things
are made or
used.
• 2 ATP are used in
step 1 and 3.
• Phosphate groups
are added to the
glucose molecule
• In step 4 & 5 the
molecule is split into
DHAP and G3P. An
enzyme converts
DHAP to G3P. This
produces two
molecules of G3P.
• Step 6 produces two
NADH (one from
each G3P).
• In step 7, two ATP
molecules are
produced by
substrate-level
phosphorylation.
• The ATP debt is
paid.
• In step 10, two ATP
molecules are
produced by
substrate-level
phosphorylation and
pyruvate is formed.
ENERGY YIELD FOR GLYCOLYSIS
4 ATP produced
2 ATP used
2 ATP produced net
2 NADH produced
2 mol ATP x 31 kJ/mol ATP = 62 kJ
Total free energy in 1 mol of glucose = 2870 kJ
Energy conversion efficiency = 62 kJ
2870 kJ
x 100% = 2.2%
STAGE 2: PYRUVATE OXIDATION
• Two pyruvate molecules are transported through
the mitochondrial membrane into the matrix and
acetyl-CoA is formed.
PYRUVATE OXIDATION
1. Carboxyl group is removed as CO2.
2. The remaining two-carbon portion is oxidized by NAD+ and
forms an acetyl group.
3. Coenzyme A attaches to the acetyl and forms acetyl-CoA.
PRODUCTS OF PYRUVATE OXIDATION
2 pyruvate + 2NAD+ + 2CoA  2acetyl-CoA + 2NADH + 2H+ + 2CO2
2 Acetyl-CoA
2 CO2
2 NADH
2
+
H
STAGE 3: THE KREBS CYCLE
• Discovered in 1937 by
Sir Hans Krebs.
• In 1953, Krebs and Fritz
Albert Lipmann shared
the Nobel Prize for their
discoveries.
• Krebs cycle is a cyclic
series of reactions that
transfers energy from
organic molecules to
ATP, NADH, FADH2 and
removes carbon atoms
as CO2.
Retrieved from: http://www.nndb.com/people/619/000129232/
• Two molecules
of acetyl-CoA
form for every
molecule of
glucose: the
Krebs Cycle
occurs twice for
each molecule
of glucose.
• CoA is recycled.
• Energy is
harvested in steps
3, 4, 5, 6, 8.
• NAD+ is reduced
to NADH in steps
3, 4, 8.
• Step 5 produces
ATP by substratelevel
phosphorylation.
• In step 6 energy is
harvested. FAD is
reduced to
FADH2.
• The C atoms from
the glucose
molecule exit the
process as CO2 in
steps 3 and 4.
• FADH2 carries less
energy than
NADH.
BY THE END OF THE KREBS CYCLE
6 carbons from
glucose
CO2
2 ATP
2 ATP
2 FADH2
glycolysis
Krebs
Krebs
2 NADH
2 NADH
6 NADH
glycolysis
pyruvate
oxidation
Krebs
STAGE 4: ELECTRON TRANSPORT AND
CHEMIOSMOSIS
• NADH and FADH2 transfer the hydrogen atom
electrons to a series of proteins in the inner
mitochondrial membrane called the electron
transport chain.
5. The whole process
is highly exergonic
and the free
energy produced
pumps H+ across
the membrane
and creates a
proton gradient.
4. At the final
complex, oxygen
oxidizes the
cytochrome
oxidase complex
and forms water.
1. The first protein complex
picks up the hydrogen
atom from NADH and Q
strips the electrons
which causes the
protein complex to let
go of the proton.
2. Q shuttles the
electrons to the
next complex. The
first protein
complex is oxidized
and the second is
reduced.
3. The electrons
become more
stable as they
move along the
chain and free
energy is released.
This energy moves
H+ across the
membrane.
NADH VS. FADH2
• NADH can pass its electrons to the first protein
complex in the ETC.
• FADH2 transfers its electrons first to Q (ubiquinone).
• NADH can pump 3 protons
• FADH2 can only pump 2 protons.
• As a result, NADH forms 3 ATP molecules and FADH2
forms 2 ATP molecules.
• NADH produced by glycolysis in the cytoplasm is
brought into the matrix by a glycerol-phosphate
shuttle and converts it to FADH2.
FINALLY: CHEMIOSMOSIS AND
OXIDATIVE ATP SYNTHESIS
• Remember: there is now an
electrochemical gradient that is
storing free energy.
• Electrical component: higher positive
charge in the intermembrane space
than the matrix.
• Chemical component: higher
concentration of protons in the
intermembrane space than the matrix.
• This gradient creates a voltage
across the membrane much like a
battery.
• The protons are unable to pass
through the phospholipid bilayer
unaided.
1. Protons cannot
diffuse across the
membrane alone.
They travel
through proton
channels
associated with
ATPase.
2. Proton-motive
force (PMF) moves
the protons
through the
ATPase.
3. The free energy
from protons moving
through the ATPase
drives the synthesis of
ATP from ADP and Pi
in the matrix.
Peter Mitchell won the
Nobel Prize in Chemistry in
1978 for discovering this
ATP generating
mechanism.
STUDENT ACTIVITY: MODEL MAKING &
VIDEOS
• http://www.youtube.com/watch?v=3rO26W1xG9U
WHAT NEXT?
• ATP molecules are
transported through the
mitochondrial
membranes by
facilitated diffusion into
the cytoplasm of the
cell where they can
drive endergonic
processes like
movement, active
transport, and synthesis
reactions in the cell.
EFFICIENCY
• Aerobic respiration captures 32% of the available
free energy of one molecule of glucose.
• Using the actual yield of 30 ATP per glucose
molecule:
• Efficiency = 30 mol ATP x 31 kJ/mol ATP / 2870 kJ x 100% =
32%
• This is much more efficient than glycolysis!
• In comparison, the energy efficiency of a car is
approximately 25%.