BIOL 112 Lecture Notes - Lecture 11: Carbon Fixation, Light-Independent Reactions, Cellular Respiration
16 May 2018
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BIOL 112- Lecture 10- Photosynthesis
Overall reaction is the opposite of cellular respiration
-!Uses CO2 and H2O to make sugar and O2
-!Plants do have mitochondria for aerobic
respiration (roots, winter, night)
Stages:
•!Light reactions: first set of reactions of
photosynthesis in which light energy excites
electrons in chlorophyll molecules, powers
chemiosmotic ATP synthesis and results in reduction of NADP+ to NADPH
o!Require chlorophyll and occur on the thylakoid membranes in
chloroplasts
o!High NADPH and ATP reduced electron carriers
o!First 2 stages
•!Reactions of the third stage result in carbon fixation- the process of incorporating
CO2 into carbohydrate molecules
o!These reactions are endergonic (dependent on light reactions for a
supply of ATP and NADPH
o!Carbon fixation takes place in stroma by a series of reactions called the
Calvin Cycle.
•!Calvin cycle/photosynthetic carbon reduction cycle: cyclic set of reactions
occurring in the stroma of the chloroplasts that fixes the carbon of CO2 into
carbohydrate molecules and recycles coenzymes
o!Used to be called dark reactions (studies now show that many enzymes
that catalyze these reactions are activated by light and are inactive in
the dark
o!Last stage
Respiration: starts with NADH and loses electrons
Photosynthesis: gives electrons to NAD to make NADPH
NADP vs NAD: they can be interconverted
-!Same properties and occur in plants and animals, but are made by separate
pathways and are independently regulated. They are used in different pathways
at different concentration
-!NADP: anabolic/biosynthetic pathways. Excess NADPH drives biosynthetic
reductions
-!NAD: catabolic pathways. Excess NAD accelerates oxidation of sugars and
generation of NADH
Light Energy:
Capture of light energy: Clusters of photosynthetic pigments called photosystems,
which are embedded in thylakoid membranes, absorb photons of particular
wavelengths and through light reactions, transfer their energy to ADP, Pi and NADP+,
forming ATP and NADPH
•!Electrons (in the form of H atoms) are needed to reduce NADP+. They are
supplied by H2O
•!ATP and NADPH are synthesized in the stroma
Wavelength:
•!Short = high energy (electromagnetic radiation causes ionization- X rays)
•!Long= low energy (vibrational energy only)- Infrared, heat
o!Small spectrum: visible light (400-700 nm)
o!Photosynthesis and vision happens with this light
•!Absorption results in colours (leftover light that was not absorbed)
•!Absorption of light energy is used in vision and photosynthesis
•!Spectrum of solar light largely corresponds to visible wavelengths
Energy absorption: electron transition to a higher energy level, which can facilitate
chemical reactions
Alternating/conjugated double bonds found in chlorophyll/beta carotene result in
delocalized electrons suitable for excitation by certain wavelengths of visible light (right
E level to absorb the right amount of light)
•!Lots of electrons available to be excited
Absorbance spectrum:
Shows wavelengths at which
chlorophyll/other pigments absorbs light
•!Each peak corresponds to an excited
state of an electron
Chlorophyll: absorbs blue and red light and
transmit green light
Carotenoids: accessory pigments that
absorb green and blue light, transmit yellow,
orange and red light
Action spectrum:
Shows wavelengths at which plants produce
the most oxygen
Oxygen: waste product of photosynthesis
reactions. The bacteria move to the
wavelength where there is the highest
amount of O2 (highest amount of
photosynthesis)
•!Little bumps in graph are cause by
carotenoids, because in most plants
there is carotenoids and chlorophylls
absorbing light energy so bacteria go
there also!
Solar spectrum:
Earth is in the perfect distance from the sun to have the right wavelength for visible
energy
•!Why are leaves orange in the fall: plant reabsorbs the “good stuff” which is
chlorophyll, and gets stored for next year, so what is left over is the carotenoids,
when carotenoids are reabsorbed leaves turn brown and they fall
Light Reactions:
1.!Photoexcitation: absorption of a
photon by an electron of
chlorophyll
2.!Electron transport: transfer of the
excited electron through a series
of membrane-bound electron
carriers, resulting in the pumping
of a proton through the
photosynthetic membrane, which
creates an H+ reserve and
eventually reduces an electron
acceptor
3.!Chemiosmosis: the movement of
protons through ATPase
complexes to drive the
phosphorylation of ADP to ATP
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BIOL 112 Full Course Notes
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Document Summary
Overall reaction is the opposite of cellular respiration. Uses co2 and h2o to make sugar and o2. Plants do have mitochondria for aerobic respiration (roots, winter, night) Co2 into carbohydrate molecules: these reactions are endergonic (dependent on light reactions for a supply of atp and nadph, carbon fixation takes place in stroma by a series of reactions called the. Photosynthesis: gives electrons to nad to make nadph. Same properties and occur in plants and animals, but are made by separate pathways and are independently regulated. They are used in different pathways at different concentration. Excess nad accelerates oxidation of sugars and generation of nadh. They are supplied by h2o: atp and nadph are synthesized in the stroma. Energy absorption: electron transition to a higher energy level, which can facilitate chemical reactions. Alternating/conjugated double bonds found in chlorophyll/beta carotene result in delocalized electrons suitable for excitation by certain wavelengths of visible light (right.
