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Photosynthesis Review
6CO2+6H20+ light = C6H12O6+ 6O2
PHOTOSYNTHESIS REVIEWED
AND EXTENDED
H2O
CO2
Chloroplast
Light
NADP+
ADP
+P
RUBP
Photosystem II
Thylakoid
membranes
Electron
transport
chains
Photosystem I
CALVIN
CYCLE 3-PGA
(in stroma)
ATP
NADPH
Stroma
G3P
Cellular
respiration
Cellulose
O2
Figure 7.11
LIGHT REACTIONS
Sugars
CALVIN CYCLE
Starch
Other organic
compounds
I. The Light Reaction
• Happens on the thylakoid membranes
• Takes energy from the sun (photons) and converts it to
energy stored in NADPH and ATP
• Energy is represented by moving electrons through the
electron transport chain
• As electrons are moved, H ions are pumped actively
from the stroma into the thylakoid space
• Some energy is used to phosphorylate ADP, so about
1.5 ATPs are produced = photophosphorylation
• As the electrons reach the end of the chain, they are
NADP is reduced to form NADPH, so NADP is the final
electron acceptor.
• The H ions now diffuse through ATP synthetase this
powers the production of ATP from ADP and P =
chemiosmosis.
• To replace the electrons lost in PSII, water is split
(photolysis), and oxygen is released into the
atmosphere.
• SEE Cliff’s Book page 54 for cyclic
– The excited electrons
• Are passed from the primary electron acceptor to
electron transport chains
Photon
Photon
Photosystem II
1
6
Thylakoid membrane
Stroma
Photosystem I NADP+ + H+
e–
2 e–
4
5
P700
P680
Thylakoid
space
Figure 7.8A
3
H2O
1 O
+
2 + 2 H
2
Electron transport chain
Provides energy for synthesis of
by chemiosmosis
ATP
NADPH
– The diffusion of H+ back across the
membrane through ATP synthase
Chloroplast
• Powers the phosphorylation of ADP to
produce ATP (photophosphorylation)
Stroma (low H+ concentration)
H+
Light
Light
H+
ADP +
H+
NADP+
+
+ H
P
NADPH
H+
Thylakoid
membrane
H2 O
H+
1
O2
+2 H+
H+
H+
H+
H+
H+
H+
2
Photosystem II
Thylakoid space
(high H+ concentration)
Electron
transport chain
Photosystem I
H+
H+
H+
ATP synthase
ATP
II.The Calvin Cycle (Dark Reaction)
• CO2 enters the cycle and combines with a 5-carbon
sugar called RuBP, ribulose biphosphate. Rubisco is the
enzyme that catalyzes this reaction.
• The 6-carbon sugar is now split into two 3-carbon
molecules called PGA (This is why we called this the C3
pathway.)
• ATP and NADPH (from the light reaction) give their
phosphates and energy to PGA to form PGAL (still a 3carbon sugar).
• 6 CO2 enter this cycle, ultimately forming 12 molecules
of PGAL.
• 10 of the PGAL (3-carbon sugars) are converted back to
6 RuBP (5-carbon sugars), so that the cycle can be
repeated.
• 2 of the PGAL will be used to build one molecule of
glucose (6-carbon sugar).
Step 1 Carbon fixation. An enzyme
called rubisco combines CO2 with a
five-carbon sugar called ribulose
bisphosphate (abbreviated RuBP). The
unstable product splits into two
molecules of the three-carbon organic
acid, 3-phosphoglyceric acid (3-PGA).
For three CO2 entering, six 3-PGA
result.
Input: 3
CO2
1
3
Step 2 Reduction. Two chemical reactions (indicated by
the two blue arrows) consume
energy from six molecules of
ATP and oxidize six molecules
of NADPH. Six molecules of 3PGA are reduced, producing
six molecules of the energyrich three-carbon sugar, G3P
Step 3 Release of one molecule
of G3P. Five of the G3Ps from step
2 remain in the cycle. The single
molecule of G3P you see leaving
the cycle is the net product of
photosynthesis. A plant cell uses
two G3P molecules to make one
molecule of glucose.
In a reaction
catalyzed by rubisco,
CO2 is added to RuBP.
P
P
P
6
RuBP
3-PGA
6
ATP
3 ADP
3
6
CALVIN
CYCLE
ATP
4
5
ADP +
2
P
6
G3P
6
NADPH
6
NADP+
P
G3P
3
Figure 7.10B
Step 4 Regeneration of RuBP. A
series of chemical reactions uses
energy from ATP to rearrange the
atoms in the five G3P molecules (15
carbons total), forming three RuBP
molecules (15 carbons).These can
start another turn of the cycle.
Output:
P
1
G3P
Glucose
and other
compounds
P
Respiration Review
6O2+ C6H12O6 = 6CO2+6H2O + 36ATPs
I. Glycolysis
• Glucose (6 carbon sugar) is broken down into 2
pyruvate (3 carbon sugars) in the cytoplasm of
the cell.
• In order to do so, 2 ATPs are added to glucose
to make a form that is more easily broken.
• As glucose is broken down, energy is released
from the bonds, and 4 ATPs are formed, as well
as 2 NADH. As the broken down glucose is
donating phosphates to ADP, this is called
substrate level phosphorylation. The electron
acceptor in this process is NAD, not NADP.
II. Conversion of Pyruvate to Acetyl-CoA
• Now the two pyruvates are going to leave the
cytoplasm and enter the mitochondrial matrix
(the inside of the mitochondria).
• It takes 2 ATPs to get them through the
membrane.
• The pyruvates will each lose a carbon, to form
CO2, and electrons to form another NADH.
These two carbons are now added to coenzyme
A to form a 2 carbon compound called Acetyl
CoA.
III. The Kreb’s Cycle aka Citric Acid Cycle
• In the matrix, the 2-carbon acetyl CoA combines with a
4-carbon OAA (oxaloacetic acid) to form a 6 carbon citric
acid.
• This 6-carbon citric acid goes through a series of
reactions where it is broken down to release 2 of the
carbons and lots of energy. In the process…
• 2 CO2 are produced
• 3 NADH are produced
• 1 FADH2 are produced
• 1 ATP
****This will happen twice, because there are two acetyl
CoA going in to the Kreb’s cycle. So, multiply the above
products by two.
SEE Page 74 in Cliff’s Book!!!!!!!!
IV. Chemiosmosis/ Oxidative
Phosphorylation
• Now all the NADHs and the FADH2s are going to donate
electrons to the electron transport chain in the cristae
membranes of the mitochondria. Just as in
photosynthesis, the electrons will move along a series of
proteins in the membrane, pumping hydrogens from the
matrix to the outer compartment of the mitochondria.
• The final electron acceptor at the end of the chain is
oxygen. When oxygen accepts the electrons, water is
produced.
• Finally, the hydrogens have now accumulated outside of
the matrix. They will diffuse in and power ATP
synthetase to produce ATP.
3 ATPs for every NADH
2 ATPs for every FADH2