Download Chapter 11

Slide 1
Chapter 11:
Phototrophic Energy
Metabolism:
Photosynthesis
Slide 2
Photoheterotrophs vs. Photoautotrophs
Slide 3
Photosynthesis Overview
• Energy Transduction Reactions (aka the “light
reactions”)
• Light energy is captured by chlorophyll
• Reducing power is generated in the form of
NADPH
• Carbon Assimilation Reactions (aka the “dark
reactions”, the Calvin cycle)
• Carbon dioxide is fixed and reduced
Slide 4
The
Chloroplast
Slide 5
Slide 6
Cyanobacterium
Slide 7
Light
• Electromagnetic radiation with both wave and particle
properties
• Photon – discreet particle of light
• Quantum – packet of energy carried by the photon
• Energy carried by photon is inversely proportional to
the wavelength
• Pigment – light absorbing molecule
• Photoexcitation – photon energy is used to excite an
electron
Slide 8
Chlorophyll
Slide 9
Photosystems
• Combination of chlorophyll molecules, accessory
pigments, and associated proteins (all arranged into a
functional unit)
• Localized to thylakoid or bacterial membranes
Slide 10
Slide 11
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Summary of Photosystems
• Electrons move from water to NADPH
• Called non-cyclic electron flow
• 4 photons absorbed in PSII, 4 in PSI, 8 total
• 2 NADPH molecules generated
• 12 protons pumped
Slide 14
ATP Synthesis
• Photophosphorylation
• Very similar to ATP synthesis in cellular respiration
• Approximately 1 ATP for every four protons
Slide 15
Cyclic Electron
Flow
Slide 16
The Calvin Cycle
• Named after Melvin Calvin
• Won a Nobel prize in 1961
• Elucidated through the use of radiolabeled isotopes
• Occurs in the stroma of chloroplasts
• Split into 3 stages:
• Carboxylation of Ribulose-1,5-Bisphosphate
• Reduction of 3-phosphoglycerate
• Regeneration of acceptor molecule
Slide 17
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Slide 19
Carbohydrate
Synthesis
Slide 20
The Glycolate Pathway
• Remember: Rubisco normally has carboxylase activity
• It also has oxygenase activity
• Produces 2 carbon molecule: phosphoglycolate
• Phosphoglycolate cannot be used in Calvin Cycle
• Why would evolution favor this?
• How do plants deal with it?
Slide 21
Slide 22
C4 Plants
• Carbon is fixed into 4 carbon molecule instead of 3
• Plants adapted to hot, arid environments with lots
of sunshine (tropical grasses, maize, sugarcane,
etc)
• Strategy: Isolate rubisco in cells that have high
CO2 levels
Slide 23
Slide 24
The HatchSlack Cycle
Slide 25
CAM plants
• Crassulacean Acid Metabolism
• Cacti, succulents, orchids, etc. (where water is limited)
• Strategy: Segregate reactions by time (rather than
space as in C4 plants)
• Only open stomata at night