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Lecture 12

BIOL 112 Lecture Notes - Lecture 12: Light-Independent Reactions, Carbon Fixation, Radiant Energy


Department
Biology
Course Code
BIOL 112
Professor
Lucy- Ann Joseph
Lecture
12

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BIOL 112-Lecture-12-photosynthesis
Steps of photosynthesis
oCapture of light energy
oThe light reactions
o Carbon fixation
photosynthesis—reverse of respiration
oATP cycle and NADPH cycle
oCalvin cycle—transfer CO2 into sugars—kind of the opposite of citric acid cycle
oDifference: energy in aerobic respiration from NADH; energy in photosynthesis
from light (but produces NADPH)
oNAD and NADP have the same properties and occur in plants and animals but
are made by separate pathways and are independently regulated.
oNADP exclusively for anabolic (biosynthetic) pathways. (drive biosynthetic
reductions)
oNAD exclusively for catabolic pathways (accelerate oxidation of sugars and
generation of NADH)
Capture of light energy
oOnly in the range of wavelength of vision (visible light)—only wavelength can be
converted into chemical energy (electron transitions transformed into chemical
energy)
oLight energy brings electrons to excited state
oAlternating/conjugated double bonds result in delocalized electrons
oChlorophylls absorb blue and red light and transmit green light
oCarotenoids absorb blue and green light and transmit yellow, orange, or red light
oWith an excited electron: pigment molecule decay, transmit light and emits heat
to bring electron to its ground sate—however, this should not happen in
photosynthesis. What happens instead: the decay of one pigment molecule
brings the neighboring molecule to excited state and so forth—electron
transportation chain.
oThe light harvesting complex—antenna system embedded in thylakoid
membrane—arrangement of chlorophyll and carotenoids. Excitation (of
electrons) travels from one molecule to the next by resonance energy transfer,
until it reaches the chlorophyll in the center (“sink”) that has the lowest energy
at excited state.
oTransfer of light energy into chemical energy occurs when the reaction center
chlorophyll gives up its excited electron to reduce pheophytin
Photophosphorylation
oPhotosystem and cytochrome complex works together to make higher proton
concentration on the thylakoid lumen side of the membrane
oProton motive force drives photophosphorylation and produces ATP
Noncyclic electron transport or Z scheme
oPhotosystem II—oxidize water—works first
oPhotosystem I—connected with photosystem II with electron transport chain
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