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Photosynthesis—chloroplasts Chloroplast structure Function allowed Large membrane surface area of the thylakoids Greater absorption of light Small space (lumen) within the thylakoids Faster accumulation of protons Stroma region similar to the cytosol of the cell Area for the enzymes necessary for the Calvin cycle to work Double membrane on the outside Isolates the working parts and enzymes from the cytosol All photosynthetic processes take place within the chloroplast (unlike respiration & mitochondria) Membrane-bound organelle with evidence of endosymbiosis own membrane, own DNA, large size Found mostly in leaves, but can be found in other plant organs
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PhotosynthesisThe details behind anabolic cellular energetics
Photosynthesis—chloroplasts •All photosynthetic processes take place
within the chloroplast (unlike respiration & mitochondria)
•Membrane-bound organelle with evidence of endosymbiosis▫own membrane, own DNA, large size
•Found mostly in leaves, but can be found in other plant organs
Chloroplast structure Function allowed
Large membrane surface area of the thylakoids Greater absorption of light
Small space (lumen) within the thylakoids Faster accumulation of protons
Stroma region similar to the cytosol of the cell
Area for the enzymes necessary for the Calvin cycle to work
Double membrane on the outside
Isolates the working parts and enzymes from the cytosol
cytochrome complex
(electron carrier)
Photosynthesis—light dependent
Ener
gy o
f el
ectr
ons
Photosystem I
Excited electron acceptor
e-Electron carrier (PQ)
H+
Electron carrier
Photosystem II
Photosynthesis—light dependent
Ener
gy o
f el
ectr
ons
cytochrome complex
(electron carrier)
Photosystem II
Excited electron acceptor
e-Electron carrier (PQ)
H+
Electron carrier
Photosystem I
NADPReductase
Photosynthesis—light dependent
Ener
gy o
f el
ectr
ons
Photosystem I
Excited electron acceptor
e-Ferredoxin (electron carrier)
NADP+ + H+
NADPH
Photosynthesis—light dependent
• Final electron acceptor is NADPH
Photosynthesis—light dependent
• Electrons replaced via photolysis of water▫ Only known system in nature where oxygen is oxidized
• As energy level of electrons falls, H+ pumped into thylakoid space, creates gradient
• Chemiosmosis results in H+ coming through ATP synthase, generating ATP in stroma
•Photophosphorylation▫The energy that is used to add a phosphate
to ADP to create ATP comes from the sun
Photosynthesis—light dependentRespiration chemiosmosis Photosynthesis chemiosmosisETC chain embedded in the membrane of the cristae
ETC embedded in the membranes of the thylakoids
Energy released when e- are exchanged from one carrier to another
Same!
Released energy used to pump H+ ions into the intermembrane space
Released energy used to actively pump H+ ions into the thylakoid space
H+ ions come from the matrix H+ ions come from the stromaH+ ions diffuse back into the matrix through ATP synthase
H+ ions diffuse back into the stroma through ATP synthase
ATP synthase catalyses the oxidative phosphorylation of ADP to form ATP
Same!
Photosynthesis—light independent•NADPH and the ATP generated in the
light dependent reactions needed to drive this process
•CO2 fixed (integrated into a non-gaseous molecule) into glucose
•Occurs in the stroma
• GP - Glycerate
3-Phosphate • TP – triose
phosphate (Glyceraldehyde 3-phosphate)
• A total of 12 ATP and 12 NADPH molecules needed for ONE glucose molecule
• TP, first molecule made in glycolysis
(these are reverse rxns)• RUBSICO—a lot of it
b/c not very efficient & it’s a part of a VERY important process—carbon fixation
Photosynthesis— light independent
Photosynthesis—rates•Three main factors you need to know that
affect photosynthetic rates:▫Light intensity▫CO2 concentration▫Temperature
•Be able to explain the different aspect of each graph in terms of why it looks the way it does▫Also be able to draw the graphs on your own
Photosynthesis—rates
▫Distance from light source and power can affect the light intensity
Photosynthesis—rates
▫As temperature increases, enzyme rates increase until the point of denaturation
Optimum temperature
Photosynthesis—rates
▫Only so much RuBP to react with (and other limitations)
50 350 500 1000 2000carbon dioxide/ppm in atmosphere
CO2
saturation for most plants
Photosynthesis—cyclic vs non-cyclic photophosphorylation
•NON-cyclic photophosphorylation
•NON-cyclic photophosphorylation•Where do the replacement electrons come from?
▫Photolysis of H2O
OFF TO THE CALVIN CYCLE
•There is a cyclic photophosphorylation too•ATP produced, NO NADPH sent to Calvin
cycleH2O
H+H+
½ O2e—
e—
Photosynthesis—cyclic vs non-cyclic photophosphorylation
Photosynthesis—cyclic vs non-cyclic photophosphorylation
• e_ gets recycled: continually providing energy to establish H+ gradient
• Occurs when light is not a limiting factor + NADPH levels are high in the chloroplasts
• Extra ATPs produced head to Calvin cycle allowing it to occur more rapidly
Photosynthesis—cyclic vs non-cyclic photophosphorylation
