Module 8 Flashcards
Photosynthesis
The process by which carbohydrates are built from carbon dioxide and water using the energy of sunlight. The conversion of light energy to chemical energy.
Photosynthetic Electron Transport Chain
A series of redox reactions in which light energy absorbed by chlorophyll is used to power the movement of electrons and photophosphorylation. In oxygenic photosynthesis, the electrons ultimately come from water and the terminal electron acceptor is NADP+.
Adenosine Triphosphate (ATP)
The main source of energy in cells.
Reduction
A chemical reaction in which a molecule gains electrons and energy.
Chloroplast
The organelle where photosynthesis takes place for eukaryotic cells.
Thylakoid
A highly folded membranous structure within chloroplasts where the light-dependent reactions of photosynthesis occur and that encloses a space called the lumen.
Stroma
The region between the inner membrane and the thylakoid membrane, where the Calvin cycle takes place.
Photosystem I
Transfers electrons to NADP+.
Photosystem II
Transfers electrons to the photoelectric electron transport chain.
Z Scheme
The energy increases at photosystem II, decreases slightly, then increases again at photosystem I.
Calvin Cycle
The process in which carbon dioxide is reduced to synthesize carbohydrates, with ATP and NADPH as the energy sources.
Carboxylation
CO2 is added to a 5-carbon molecule.
Regeneration
Remaking of the 5-carbon molecule needed for phase 1.
Triose Phosphate
A phosphorylated 3-carbon sugar (carbohydrate), produced by the Calvin cycle and exported from the chloroplast.
Chlorophyll
The major light-absorbing pigment contained in the photosynthetic membranes of eukaryotes and cyanobacteria. It plays a key role in the cell’s ability to capture energy from sunlight. Appears green because it is poor at absorbing green wavelengths.
Nicotinamide Adenine Dinucleotide Phosphate (NADPH)
An electron carrier in many biochemical reactions. The reducing agent used in the Calvin cycle during photosynthesis.
Oxidation
A chemical reaction in which a molecule loses electrons and energy.
Carbohydrate
An organic molecule containing C, H, and O atoms that provides a source of energy for metabolism and that forms the starting point for synthesis of other organic molecules.
Lumen
A fluid-filled compartment enclosed by the thylakoid membrane.
Grana
Interlinked stacks of thylakoids in chloroplasts.
Antenna Chlorophyll
A chlorophyll molecule that absorbs energy from sunlight and passes it to another chlorophyll molecule during photosynthesis.
Reaction Center
Specially configured chlorophyll molecules where light energy is converted into electron transport.
Photophosphorylation
The process by which energy from sunlight drives the movement of electrons along an electron transport chain, leading to the synthesis of ATP.
Cyclic Electron Transport
Electrons from photosystem I are redirected from ferredoxin (Fd) to Pq to reenter the photosynthetic electron transport chain.
Ribulose Bisphosphate Carboxylase Oxygenase/Rubisco
The enzyme that catalyzes the carboxylation reaction in the Calvin cycle.
Photosynthesis Stages
1) Light Capture
2) Carbon Fixation
Light Capture
Energy from sunlight is captured into usable chemical forms.
Carbon Fixation
The process by which inorganic molecules, such as CO2, are converted into organic molecules, such as carbohydrates.
Pigments
Molecules that absorb some or all wavelengths of visible light. Contain a chromophore.
Visible Light
The portion of the electromagnetic spectrum apparent to our eyes (400 nm to 750 nm).
Photosystems
A protein-pigment complex that absorbs light energy to drive REDOX reactions and thereby sets the photosynthetic electron transport chain in motion.
Accessory Pigments
A light-absorbing pigment other than chlorophyll in the photosynthetic membrane.
Carotenoids
Are an important accessory pigment because they can absorb wavelengths of visible light that are poorly absorbed by chlorophyll.
Cytochrome-b6f Complex (Cyt-b6f)
Part of the photosynthetic electron transport chain, through which electrons pass between photosystem II and photosystem I.
Calvin Cycle Phases
1) Carboxylation
2) Reduction
3) Regeneration
Reduction (Calvin Cycle)
Energy and electrons are transferred.
Ribulose 1,5-bisphosphate (RuBP)
The 5-carbon sugar to which carbon dioxide is added by the enzyme rubisco.
3-phosphoglycerate (3-PGA)
A 3-carbon molecule. During the Calvin cycle, two molecules of 3-PGA are the first stable products following the addition of carbon dioxide.
Reactive Oxygen Species
Highly reactive forms of oxygen. Can cause substantial damage to the cell.
Xanthophylls
Yellow-orange carotenoid pigments that slow the formation of reactive oxygen species by reducing excess light energy. They accept absorbed light energy directly from chlorophyll and then convert this energy to heat.
Photorespiration
A process in which rubisco acts as an oxygenase, resulting in release of carbon dioxide and a net loss of energy.
Structure of Chlorophyll
1) Porphyrin Ring
2) Phytol Side Chain
Porphyrin Ring
Used for light absorption. Mg in the center. Different side groups on the ring give different types of chlorophyll.
Phytol Side Chain
Used for insertion of chlorophyll in lipid bilayer (thylakoid membrane).
Plastoquinone (Pq)
Carries electrons from PSII to the cytochrome b6f complex.
Plastocyanin (Pc)
Carries electrons from the cytochrome b6f complex to PSI by diffusing through the thylakoid lumen.
Photic Zone
In the ocean, photosynthesis occurs in the surface layer about 100 m deep. Areas in the water where sunlight is present.
Ways to Re-Establish Ground State
1) Dissipate energy as heat.
2) Re-emit energy in a longer wavelength (fluorescence).
3) Transfer energy to another molecule (happens with photosynthetic pigments).
Chromophore
Chemical groups capable of absorbing light wavelengths.
Flow of Electrons
1) Between H2O and PSII.
2) Between PSII and PSI (electron transport chain).
3) Between PSI and NADP+.
Evolution of 2 Photosystems
1) Horizontal gene transfer.
2) Gene duplication and divergence of one of the genes.
Photosynthetic Eukaryotes
1) The first organisms to use water as the electron donor were the cyanobacteria.
2) The endosymbiotic theory proposes that a cyanobacterium was engulfed by a eukaryotic cell.
3) Over time, the cyanobacterium lost the ability to live outside the host thus it became the organelle we know as the chloroplast.
