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Energy Metabolism: Photosynthesis (Photosynthesis (Light-dependent…
Energy Metabolism: Photosynthesis
Energy and Reducing Power
Energy Carriers
Energy enters the world through photosynthesis
Guanosine Triphosphate
Photophosphorylation
Light energy
Substrate-level phosphorylation
Oxidative Phosphorylation
ADP-->ATP
Reducing Power
Oxidation Reaction
Increases the positive charge on an atom
Oxidized compounds
Contain oxygen
Oxidizing agents
NAD+/NADP+
Reduction reaction
Reduces positive charge on an atom
Reduced carriers
Contain hydrogen
Reducing agents
NADH/NADPH
Reduction and Oxidation reactions occur simultaneously
Other Electron Carriers
Cytochromes
Cofactor
Heme (holds an Fe atom)
Integral membrane proteins
Thylakoid membrane
Plastoquinones
Long hydrocarbon tails=hydrophobic
Carry 2 protons and 2 electrons
Short distance electron carriers
Plastocyanin
Copper atom (+2 oxidation state)
Loose association with chloroplast membranes
Photosynthesis
Light-dependent reactions
Thylakoid reactions
The Nature of Light
Electromagnetic spectrum
Photons
Gamma rays
X-Rays
Short wavelengths
Large amounts of energy
Large wavelengths
Low amounts of energy
The Nature of Pigments
Pigmnents
Distinctive color
Associated absorbance of respective wavelengths of light
Action spectrum
Photosynthetic pigments
Chlorophyll a
Accessory pigments
Chlorophyll b
B-carotene
Resonance
Antenna complex
Reaction center
Photosynthetic unit
Activated pigments
Ground state
Excited states
Fluorescence
Photosystem 1
p700-->Absorb red light
Fx (Fe4S4)
Ferredoxin
Reduced ferredoxin is a strong reducing agent
Ferredoxin-NADP-Reductase
#
NADP-->NADPH
Is oxidized during the process, needs to be reduced for stability and continuity of photosynthetic processes
Production of NADPH
Photosystem 2
Reduction of p700 in photosystem 1
#
Backwards process of PS1
Plastocyanin donates an electron to p700
#
Oxidized plastocyanin reduced by cytochrome b6/f complex
Cytochrome b6/f reduced by plastoquinone
Carrier Q
Phaeophytin
p680
Gets new electrons from H2O
Electron Transport Chain
The Synthesis of ATP
Generated by light reactions
Chemiosmotic phosphorylation
ATP synthetase
CF0-CF1 complex
Grana(um)
Frets
Stroma
Thylakoid lumen
Enzymes and Electron carriers
Membrane impermeable to protons produced by hydrolysis
protons attached to NADP+ by Ferroxin-NADP-Reductase
Noncyclic electron transport
Does not produce enough ATP
Electrons transported to plastoquinones in PS2
Cyclic Electron Transpor
Stroma reactions
Dark reactions
production of carbohydrates
Calvin/Benson cycle/C3 cycle
RuBP
RUBISCO
3-phosphoglycerate
1,3-diphosphoglycerate
Reuced by NADH
PGAL
https://study.com/academy/lesson/photosynthesis-ii-the-calvin-benson-cycle-dark-reactions.html
Anabolic Metabolism
PGAL is an incredibly diverse building block
Anabolism
Anabolic reaction
Short term usage:ATP and NADPH
Intermediate-term storage: simple sugars
Long term storage: Starch
Synthesis of Polysaccharides
Gluconeogenesis
Glucose-6-phosphate
Fructose-1,6-phosphate
Dihydroxyacetone phosphate
Amylose
Amylopectin
Environmental and Internal Factors
Light
Quality
Colors of wavelengths
Quantity
Light intensity or brightness
Cloudy v. Sunny day
Time of day
Duration
number of hours per day that sunlight is available
Light compensation point
Leaf Structure
Temperate and Tropical plants
Standard
Excellent for absorbing CO2,
Poor for conserving water
Palisade parenchyma above
Spongy mesophyll below
Water
[H2O] available greatly affects rate of photosynthesis
Stomata open during the day, close during the night to conserve H2O
CO2 absorbed through opening of stomata
C4 Metabolism/Crassulacean Acid Metabolism
C4 Metabolism
RuBP occasionally binds to oxygen in low [CO2]
Produces 1 3-phosphoglycerate
Photorespiration
2 molecules of CO2
Extremely Exergonic
Wasteful
Protection from RuBP binding to Oxygen, but costly
30% loss of ATP and NADPH
Produces 1 phosphoglycolate
Transported to peroxisomes/lysosomes-->amino acids
RuBP evolved during very low atmospheric [O2]
RuBP sequestered to areas of High [CO2] in cell
Krenz anatomy
PEP carboxylase
PEP carboxylated
#
https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/v/c-4-photosynthesis
Crassulacean Acid Metabolism
Improves conservation of H2O
Crassulaceae
Succulent Leaves
Opening of stomata at night
Coolness of night reduces transpiration
PEP is carboxylated
Reduction to malate or other acids
Storage of CO2
Occurs at night
Acids broken down during the day and utilized in C4 metabolism
Not particularly efficient
Selectively advantageous in hot, dry climate
Prioritization of survival over growth
