Bio 229 Photosynthesis

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Photosynthesis

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Use of solar energy that drive anabolic pathways.

Major steps: Light harvesting, electron transport and proton pumping, atp synthesis, calvin cycle, starch synthesis, and sucrose synthesis.

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Phototrophs

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Organisms that convert light energy into chemical energy in the form of ATP and NADPH

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Photoheterotrophs

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Organisms that acquire energy from sunlight but depend on organic sources to live.

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Photoautotrophs

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Organisms that use solar energy to build energy rich organic molecules from inorganic starting material.

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Energy transduction reactions

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Reactions where light energy is captured by chlorophyll and converted into chemical energy in the form of ATP and NADPH.

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Carbon assimilation reactions

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Known as the calvin cycle, fully oxidized carbons from CO2 are fixed and reduced, forming carbohydrates.

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Oxygenic autotrophs

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In these organisms, water is the electron donor and light energy absorbed by chlorophyll powers movement of two electrons from water to NADP + , which is reduced to NADPH.

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Anoxygenic autotrophs

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compounds such as sulfide (S 2- ) , thiosulfate

(S 2 O 32- ) , or succinate serve as electron donors, and oxidized forms of these compounds are released.

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Stroma

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Chloroplast matrix with enzymes for carbon, nitrogen, and sulfur reduction and assimilation.

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Thylakoids

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Flat, saclike structures suspended in the

stroma. Creates an internal compartment.

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Photochemical reduction

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The transfer of the photoexcited electron itself to another molecule.

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Chlorophyll A

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Absorption spectrum between 420-660 nm. Has a formyl group (CHO).

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Bacteriochlorophyll

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Subfamily of chlorophyll molecules restricted to anoxygenic phototrophs (photosynthetic bacteria) and is characterized by a saturated site

not found in other chlorophyll molecules.

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Accessory pigments

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Absorb photons that cannot be cap-

tured by chlorophyll. They then transfer the energy of these photons to a chlorophyll molecule by resonance energy transfer.

carotenoids and phycobilins

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Carotenoids

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Include beta-carotene and lutein. Confer an orange or yellow tint to leaves and carrots.

Absorption maxima between 420 and 480 nm

absorb photons from a broad range of the blue region of the spectrum and thus appear yellow.

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Phycobilin

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Common examples are phycoerythrin and

phycocyanin.

Phycoerythrin absorbs photons from the blue, green, and yellow regions of the spectrum. Appearing red.

Phycocyanin bsorbs photons from the

orange region of the spectrum, appearing blue.

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Photosystems

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Chlorophyll molecules, accessory pigments, and associated proteins are organized into functional units localized to thylakoid or photosynthetic bacterial membranes.

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Chlorophyll-binding proteins

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Stabilize the chlorophyll within a photosystem

and modify the absorption spectra of specific chlorophyll molecules.

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Antenna pigments

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Collect light energy much like a radio antenna collects radio waves. absorb photons and pass the energy to a neighboring chlorophyll molecule or accessory pigment by resonance energy transfer.

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Reaction Center

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Start of where events that drive electron flow and proton pumping begin in a photosystem.

Chlorophyll a molecules known as the special pair catalyzes the conversion of solar energy into chemical energy.

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Light harvesting complex (LHC)

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Collects light energy and passes it on to a photosystem by resonance. They are able to move towards where light is.

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Phycobilisome

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The LHC in algea and cyanobacteria.

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Photosystem complex

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A photosystem and its associated LHC's.

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Photosystem I (PSI)

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A photosystem with an absorption maximum of 700 nm. Works together with PSII

Chlorophyll P700

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Photosystem II (PSII)

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Absorption maximum of 680 nm. Works PSI.

Chlorophyll P680.

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Special Pair

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Pair of chlorophyll a molecules that will have the electrons that are photo-excited after proton absorption.

In photosystem II its is chlorophyll P680

In photosystem I it is chlorophyll P700.

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NADP+

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A coenzyme that serves as an electron carrier. Transports excited electrons from chlorophyll. Forms NADPH when reduced.

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Photoreduction

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When electrons excited by photons are given to an electron acceptor. Involved in electron transport chain similar to respiration.

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Plastoquinone

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A molecule similar to coenzyme Q.

Qa and QB are examples.

Turns into plastoquinol when reduced.

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Oxygen-evolving complex (OEC)

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A feature of PSII that catalyzes the splitting and oxydation of water, producing O2, electrons, and protons.

Complex catalyzed by four photons.

Splitting of water is photolytic.

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Cytochrome b6/f complex

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Analogous to respiratory complex III in mitochondria. Composed of even distinct integral membrane proteins, including two cytochromes and an iron-sulfur protein.

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Q cycle

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For every electron from QbH2 to plastocyanin (PC), one of these electrons is used in the Q cycle to reduce another molecule of Qb associated with cytochrome b6.

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Calvin cycle

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The fundamental pathway for the move-

ment of inorganic carbon into the biosphere. Composed of three stages.

Carbon fixation, reduction, and regeneration of the CO2 acceptor RuBP.

Takes place in stomata.