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CHAPTERS 9 & 10
CELLULAR ENERGETICS
Cellular Respiration
&
Photosynthesis
• Which organelles are involved?
• How does the shape of each organelle
facilitate its function?
• What are the ultimate goals of these two
processes?
– Cellular respiration
– Photosynthesis
Growth, reproduction and dynamic
homeostasis require that cells create and
maintain internal environments that are
different from their external environments.
Essential knowledge 2.B.3: Eukaryotic cells
maintain internal membranes that partition the
cell into specialized regions.
a. Internal membranes facilitate cellular processes by
minimizing competing interactions and by increasing
surface area where reactions can occur.
b. Membranes and membrane-bound organelles in
eukaryotic cells localize (compartmentalize)
intracellular metabolic processes and specific
enzymatic reactions.
Essential knowledge 2.A.2: Organisms capture and store
free energy for use in biological processes.
a. Autotrophs capture free energy from physical sources
in the environment.
Evidence of student learning is a demonstrated
understanding of each of the following:
1. Photosynthetic organisms capture free energy present in
sunlight.
2. Chemosynthetic organisms capture free energy from small
inorganic molecules present in their environment, and this
process can occur in the absence of oxygen.
Essential knowledge 2.A.2: Organisms capture and store
free energy for use in biological processes.
b. Heterotrophs capture free energy present in carbon
compounds produced by other organisms.
Evidence of student learning is a demonstrated
understanding of each of the following:
1. Heterotrophs may metabolize carbohydrates, lipids and
proteins by hydrolysis as sources of free energy.
2. Fermentation produces organic molecules, including alcohol
and lactic acid, and it occurs in the absence of oxygen.
✘✘ Specific steps, names of enzymes and intermediates
of the pathways for these processes are beyond the
scope of the course and the AP Exam.
Essential knowledge 2.A.2: Organisms capture and store
free energy for use in biological processes.
c. Different energy-capturing processes use different types of
electron acceptors.
To foster student understanding of this concept,
instructors can choose an illustrative example such as:
• NADP+ in photosynthesis
• Oxygen in cellular respiration
Essential knowledge 2.A.2: Organisms capture and store
free energy for use in biological processes.
d. The light-dependent reactions of photosynthesis in
eukaryotes involve a series of coordinated reaction
pathways that capture free energy present in light to yield
ATP and NADPH, which power the production of organic
molecules.
Evidence of student learning is a demonstrated
understanding of each of the following:
1. During photosynthesis, chlorophylls absorb free energy from
light, boosting electrons to a higher energy level in
Photosystems I and II.
Essential knowledge 2.A.2: Organisms capture and store
free energy for use in biological processes.
2. Photosystems I and II are embedded in the internal
membranes of chloroplasts (thylakoids) and are connected
by the transfer of higher free energy electrons through an
electron transport chain (ETC). [See also 4.A.2]
3. When electrons are transferred between molecules in a
sequence of reactions as they pass through the ETC, an
electrochemical gradient of hydrogen ions (protons) across
the thykaloid membrane is established.
4. The formation of the proton gradient is a separate process,
but it is linked to the synthesis of ATP from ADP and
inorganic phosphate via ATP synthase.
5. The energy captured in the light reactions as ATP and
NADPH powers the production of carbohydrates from
carbon dioxide in the Calvin cycle, which occurs in the
stroma of the chloroplast.
✘✘ Memorization of the steps in the
Calvin cycle, the structure of the
molecules and the names of
enzymes (with the exception of ATP
synthase) are beyond the scope of
the course and the AP Exam.
• e. Photosynthesis first evolved in
prokaryotic organisms; scientific
evidence supports that prokaryotic
(bacterial) photosynthesis was
responsible for the production of an
oxygenated atmosphere; prokaryotic
photosynthetic pathways were the
foundation of eukaryotic photosynthesis.
f. Cellular respiration in eukaryotes involves a series of
coordinated enzyme-catalyzed reactions that harvest free
energy from simple carbohydrates.
Evidence of student learning is a demonstrated
understanding of each of the following:
1. Glycolysis rearranges the bonds in glucose molecules,
releasing free energy to form ATP from ADP and inorganic
phosphate, and resulting in the production of pyruvate.
2. Pyruvate is transported from the cytoplasm to the
mitochondrion, where further oxidation occurs
3. In the Krebs cycle, carbon dioxide is released from organic
intermediates ATP is synthesized from ADP and inorganic
phosphate via substrate level phosphorylation and
electrons are captured by coenzymes.
4. Electrons that are extracted in the series of Krebs cycle
reactions are carried by NADH and FADH2 to the electron
transport chain.
✘✘ Memorization of the
steps in glycolysis and the
Krebs cycle, or of the
structures of the molecules
and the names of the
enzymes involved, are
beyond the scope of the
course and the AP Exam.
g. The electron transport chain captures free energy from
electrons in a series of coupled reactions that establish an
electrochemical gradient across membranes.:
1. Electron transport chain reactions occur in chloroplasts
(photosynthesis), mitochondria (cellular respiration) and
prokaryotic plasma membranes.
2. In cellular respiration, electrons delivered by NADH and FADH2
are passed to a series of electron acceptors as they move
toward the terminal electron acceptor, oxygen. In
photosynthesis, the terminal electron acceptor is NADP+.
3. The passage of electrons is accompanied by the formation of a
proton gradient across the inner mitochondrial membrane or the
thylakoid membrane of chloroplasts, with the membrane(s)
separating a region of high proton concentration from a region
of low proton concentration. In prokaryotes, the passage of
electrons is accompanied by the outward movement of protons
across the plasma membrane.
4. The flow of protons back through membrane-bound
ATP synthase by chemiosmosis generates ATP from
ADP and inorganic phosphate.
5. In cellular respiration, decoupling oxidative
phosphorylation from electron transport is involved in
thermoregulation.
✘✘ The names of the specific electron carriers in
the ETC are beyond the scope of the course and
the AP Exam.
h. Free energy becomes available for metabolism by
the conversion of ATP→ADP, which is coupled to
many steps in metabolic pathways.
CHAPTER 9
CELLULAR RESPIRATION:
HARVESTING CELLULAR
ENERGY
PROTEINS ---> ATP
LIPIDS ---> ATP
CARBS (glucose) ---> ATP
THE BIG PICTURE…
ENERGY TRANSFERS
OVERVIEW:
SUNLIGHT -->
PRODUCER -->
PRIMARY CONSUMER
(HERBIVORE) -->
DECOMPOSERS -->
All release heat… all energy
returns to space eventually
RADIANT ENERGY
(PHOTONS)
CHEMICAL ENERGY STORAGE
(GLUCOSE)
CHEMICAL ENERGY
(ATP)
(POWERS CELLULAR WORK)
HEAT
RADIANT ENERGY
(PHOTONS)
CHEMICAL ENERGY
(GLUCOSE)
CHEMICAL ENERGY
(ATP)
(POWERS CELLULAR WORK)
HEAT
Metabolism? Anabolism?
Catabolism?
• Metabolism is the sum total of all an
organisms chemical reactions.
• Anabolism is the sum total of the RXNs
requiring energy that synthesizes complex
molecules from simpler ones.
• Catabolism is the opposite of anabolism.
THE HISTORY OF ENERGY USE
• The earliest organisms were PROKARYOTESarchaebacteria
• which lived 3.5 BYA
• Got their energy from digesting organic
compounds in the water
• Some of these creatures evolved into autotrophic
prokaryotes that made their own food via
photosynthesis or chemosynthesis.
• Chemosynthesis- energy to synthesize
carbohydrates comes from chemicals not light.
• Processes of glycolysis (breaking glucose to
make ATP) and an ANAEROBIC (w/out
oxygen) process evolved first...
• By 2.7 BYA oxygen had accumulated in the
atmosphere (because of the photosynthetic
bacteria that had evolved).
• By 2.0 BYA Eukaryotic cells had evolved w/
their high metabolic needs... Hence the
evolution of aerobic respiration (uses
oxygen as final electron acceptor).
Do chemosynthetic creatures
still exist today???
• Yes, bacteria that
get their energy from
hydrogen sulfide,
ammonia, or ferrous
ions, or minerals in
stone.
• EATING AWAY at
famous statues!
• Yes, creatures that
live off hydrothermal
vents on the ocean
floor (far from
sunlight!)
Methanobacteria- These bacteria inhabit wetlands, areas
high in sewage and intestinal tracts. They combine carbon
dioxide and hydrogen, which frees the oxygen that they
need to live and produces methane as a byproduct.
Cellular Respiration
•
Is the metabolic pathway(s) that create ATP
for the organism for cellular work.
• The amount of ATP generated and
particular “pathway” is influenced by the
presence or absence of oxygen.
• Thus:
1) Anaerobic Respiration (fermentation)
2) Aerobic Respiration
Sequence of Events for incomplete
anaerobic glucose metabolism
1) Glycolysis (2 ATP)
2) Fermentation (alcohol or lactic acid)
*much energy is left over in the final
products (alcohol or lactic acid)- not
converted to carbon dioxide.
Sequence of Events for full
glucose metabolism
(aka: aerobic respiration)
1) Glycolysis (2 ATP)
2) Oxidation of pyruvic acid to acetyl CoA
(lose CO2)
3) Krebs Cycle (citric acid&ATP) (lose CO2)
4) Electron Transport Chain
5) ATP synthesis via chemiosmosis
TOTAL ATP PRODUCTION IS 38ATP
AEROBIC RESPIRATION
STEP #1: GLYCOLYSIS
STEP #2: THE KREBS CYCLE
STEP 3: NADH & FADH2 CARRY ELECRONS TO
ELECTRON TRANSPORT CHAIN -> CHEMIOSMOSIS
Notice…
• Aerobic Respiration yield of ATP is also
called
• “Oxidative Phosphorylation”
• What is oxidation?
REDOX: The Energy Rxns
transferring electrons
• Oxidation is the loss of electrons from
one substance.
• Ex. Na -> Na+
NADH -> NAD+ , e-, e-, H+
• Reduction is the addition of electrons
to another substance.
• Ex. Cl -> ClNAD+ plus (e-, e-, H+) -> NADH
• OIL RIG• Oxidation is Losing
• Reduction is Gaining
• LEO GER• Losing electrons is OXIDATION
• Gaining electrons is REDUCTION
CHARACTERISTICS
• Oxidation-reduction REDOX reactions are
coupled.
• They transfer electrons from one reactant to
another.
SUMMARY EQUATION FOR
CELLULAR RESPIRATION
• C6H12O6 + 6 O2 -> 6 CO2 + 6 H20 + 38 ATP
• Oxidation: C6H12O6 -> 6 CO2
Glucose is oxidized
Lost e- and hydrogens
• Reduction: 6 O2 -> 6 H20
Oxygen is reduced
Gained e- and hydrogens
* Note- this does not happen DIRECTLY. Electrons
are transferred via “electron carrier molecules”.
• Electrons fall
from organic
molecules to
oxygen during
cellular
respiration.
• Organic
molecules with
an abundance of
hydrogen are
excellent fuels
• their bonds are a
source of hilltop
electrons with
the potential to
fall closer to
oxygen.
Electrons from Hydrogen travel down electron
Transport chain with Oxygen as the
Electro-negative SINK for electrons
Slowly releases energy --> forms water.
Protons form a concentration gradient… will result in ATP!!!
ENERGY CARRYING
MOLECULES
(used for cellular work)
ATP
&
Coenzymes that are involved in the metabolic
pathways of respiration and photosynthesis
NADH
FADH2
NADPH
These last three are called “electron carriers”
ATP
ADENOSINE TRI-PHOSPHATE
ADP
ATP
ATP
“energy carrier molecule “
Energy is
stored in the
bonds between
phosphate
groups.
ATP
• : adenosine tri phosphate
• : adenosine nucleotide
3 phosphate groups
• : high energy bonds are between the
phosphates
• : ATP releases energy by using a phosphate
group to phosphorylate other molecules thus
degrading to ADP.
• : -7.3 kcal/mol
How is ATP regenerated?
1) SUBSTRATE LEVEL
phosphorylation
2) OXIDATIVE
PHOSPHORYLATION
Chemiosmosis through
ATP-synthase
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
NAD+
NADH
NADH
“electron carrier molecule “
NAD+/NADH is a coenzyme
NAD+ accepts 2e- & H+
NADH is the ENERGY RICH form
THE OTHER H+ STICKS AROUND
FADH
FAD
VV 2
“electron carrier molecule “
FAD/FADH2
is a coenzyme
FAD accepts
2e- & 2H+
FADH2 is the
ENERGY RICH
molecule
GLYCOLYSIS: BREAKING
DOWN GLUCOSE
• Glycolysis happens in the cytosol of the cell.
• Key Players:
enzymes- one at every step
ATP- the goal
ADP + Pi
NAD+
NADH (a.k.a. NADH + H+)- w/ 2e-/H+
PGAL- CCC-P
Pyruvic Acid(a.k.a. pyruvate)- CCC
Figure 9.8 The energy input and output of glycolysis
Glycolysis = breaking glucose
Energy Investment:
1. 2 ATP needed
Energy Payoff:
1. 2 NADH formed
2. 4 ATP formed
3. 2 pyruvate remain
NET GAIN
2,2,2
IMPORTANT EVENTS USED PRODUCED
1.
2.
3.
4.
Glucose
Add phosphate
ATP
ADP, Pi
Add phosphate
ATP
ADP, Pi
Split into 2 3Carbon
PGAL molecules
5.2PGAL oxidized and 2NAD+
2NADH, 2H+
NAD+ is reduced to
NADH while phosphate
is added to PGAL
6. ADP takes away Phosphate 2ADP 2ATP
7. Water is taken out
8. ADP takes away phosphate 2ADP 2ATP
9. Pyruvic acid is created.
KNOWING THE DETAILS IS BEYOND THE SCOPE OF AP BIO
Glycolysis:
phase 1- energy investment
ENERGY INVESTMENT
PHASE
PHOSPHORYLATION BY
REDOX NOT USING ATP
NAD+ IS REDUCED
Energy Payoff
Phase
WHAT JUST HAPPENED?
• 1) one molecule of glucose is broken down into 2
molecules of pyruvic acid/ pyruvate.
• 2) two molecules of ATP are used but FOUR new
molecules are generated, for a net gain of 2 ATP.
• 3) two molecules of NADH are formed.
Faculatative
Anaerobes
Use oxygen
to make a lot
of ATP when it
is present.
Otherwise,
regenerate
NAD+ via
fermentation
and just live
off the 2 ATP
from glycolysis
The Next Step: When Oxygen
is NOT around
Both molecules of pyruvic acid udergo fermentation in
the absence of oxygen.
In animals: NADH (from glycolysis) is oxidized (releases
hydrogen) while pyruvic acid is reduced (adds
hydrogen). The new molecule is lactic acid.
In yeast: The three-carbon pyruvic acid molecule is
broken into a 2 carbon compound (acetylaldehyde)
and CO2 is released. NADH (from glycolysis) is
oxidized (releases hydrogen) while the two carbon
compound is reduced (adds hydrogen).
The new molecule is ethyl alcohol.
Fermentation only releases about
3.5% of the kilocalaries available in glucose
What is the goal of
fermentation?
• Regenerate NAD+ for glycolysis
• It is needed at the beginning of the
energy payoff stage to phosphorylate
the molecules.
Figure 9.x2 Fermentation
ALCOHOL FERMENTATION
Alcoholic fermentation
LACTIC ACID FERMENTATION
LACTIC ACID FERMENTATION
The end…
What are coupled reactions
and how do they work?
• Endergonic + Exergonic
• Exergonic one lends energy to the
endergonic one.
• Aerobic respiration- the catabolism of pyruvate
• takes place in the mitochondrion
• (requires O2)oxygen acts as the final electron
acceptor or oxidizing agent because it is
reduced
• (very electronegative- acts like an electron sink)
Sequence of Events
1) Glycolysis
2) Oxidation of pyruvic acid to acetyl CoA
(lose CO2)
3) Krebs Cycle (citric acid)
4) Electron Transport Chain
5) ATP synthesis
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis
and the Krebs cycle
Getting pyruvate into the
Matrix
1) Carboxyl group of pyruvate is removed as 1
molecule of CO2.
2) Remaining 2 carbon molecule is oxidized to
form ACETATE-> 2 e- and 1 H+ are
transferred to NAD+ to form NADH.
3) CoenzymeA picks up ACETYL group->
acetyl-CoA
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis
and the Krebs cycle
THE KREBS CYCLE
1. Coenzyme A attaches
acetyl to OAA
2. Citrate/citric Acid
formed
3. Decarboxylation
(CO2 released)
Redox- NADH formed
4. Decarboxylation
(CO2 released)
Redox- NADH formed
5. ATP formed
6. Redox- FADH2 formed
7. Redox- NADH formed
OAA reformed
Figure 9.12 A summary of the Krebs cycle
THE KREBS CYCLE
•
Discovered by HANS KREBS in the 1930s (britishgerman)
1) Acetyl-CoA adds 2 carbon fragment to OAAoxaloacetate which forms citrate/citric acid.
2) Citrate loses a CO2, compound is oxidized, NAD+
is reduced to NADH.
3) Another CO2 lost, compounds oxidized, NAD+
reduced to NADH.
4) CoA replaced by P ->GDP->GTP->ATP
5) FAD is reduced to FADH2
6) H20 added, substrate oxidized, NAD+ reduced to
NADH-> OAA
Figure 9.11 A closer look at the Krebs cycle (Layer 1)
Figure 9.11 A closer look at the Krebs cycle (Layer 2)
Figure 9.11 A closer look at the Krebs cycle (Layer 3)
Figure 9.11 A closer look at the Krebs cycle (Layer 4)
•
•
•
•
•
•
•
•
•
•
•
•
How many turns/glucose?
Two
NET RESULTS per glucose:
ATP?
Two
NADH?
Six
FADH2?
2
CO2?
4
WHAT HAPPENED TO Carbon, Oxygen, &
Hydrogen of GLUCOSE?
• CO2 & NADH, FADH2
Figure 9.13 Free-energy change during electron transport
THE ELECTRON
TRANSPORT CHAIN
• What is it?
• Collection of molecules embedded in the
inner mitochondrial membrane.
– Proteins (cytochromes)
– Coeznymes (Q)
• Folds = cristae = increased surface area for
more reactions!
• Moving electrons power the proton pumps
Main events:
NADH
1) Dumps 2 electrons
2) H+, NAD+ made
FADH2
1) Dump 2 electrons
2) 2 H+, FAD made
The electrons pass down the ETC which is
made of CYTOCHROMES- iron containing
proteins that transfer electrons.
Final Step= attach to O2 & H+ to make water.
THE RESULTS
1) Exergonic flow of e- pumps H+ ions
(protons) across membrane to Inter
Membrane Space.
2) Ion gradient (H+/proton gradient) is
created- this PROTON MOTIVE
FORCE can do work.
CHEMIOSMOSIS
ATP synthase = enzyme
that makes ATP from ADP
& P.
It is an ion pump in reverse.
When the ions enter ATP
synthase it turns the protein
rotor- causing change in
shape of the enzyme.
Electron Transport Chain
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
Figure 9.16 Review: how each molecule of glucose yields many ATP molecules
during cellular respiration
HOW MUCH ATP IS
PRODUCED/glucose?
•
•
•
•
•
Each NADH: 3 ATP (10x3=30 chemiosmosis)
Each FADH2: 2 ATP (2x2=4 chemiosmosis)
Total ATP from breakdown of glucose:
4 glycolysis+2 Krebs Cycle+34 ETC= 40)
However, 2 are used during glycolysis so the
net amount is 38!
• And some ATP is used to shuttle NADH into
the matrix that is created by glycolysis.
Figure 9.20 The control of cellular respiration
GLYCOLYSIS
THE KREBS CYCLE
ELECTRON TRANSPORT
CHAIN
LAB #5 Cell Respiration
Next Class
• Extra credit to set up tomorrow during
7th period. You can only earn this extra
credit once, but you are welcome to
help if you just want to prep for the lab.
• Don’t forget to do the LAB BENCH
exercise and write your prelab notes.