Chapter 10 - Photosynthesis

Terms Definitions
Carbon Fixation
- Incorporating CO2 from the air into organic molecules already present in the chloroplast
- The initial incorporation of carbon into organic compounds
- Substances that absorb visible light
- Different pigments abosrb light of different wavelengths
- ex: we see green when we look at a leaf because chlorophyll absorbs violet-blue and red light while transmitting and reflecting green light
Chlorophyll a
- the primary pigment in chloroplasts
- participates directly in the light reactions
- Contains a methyl group attached to its porphyrin ring. Appears blue-green
Action Spectrum
- Profiles the relative effectiveness of different wavelengths of radiation in driving the process.
- prepared by illuminating chloroplasts with light of different colors and then plotting wavelength against some measure of photosynthetic rate (i.e. CO2 consumption or O2 release)
Absorption Spectrum
- A graph plotting a pigments light absorption versus wavelength
- The three curves show the wavelengths of light best absorbed (blue-violet and red) by three types of chloroplasts
Engelmann's Experiment
- In 1883 Engelmann illumated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light.
chlorophyll b
- An accessory pigment that has a -CHO group (instead of a methyl group) attached to its porphyrin ring. Appears olive green.
- An accessory pigment that has hydrocarbons that are various shapes of yellow and orange because they abosrob violet and blue-green light
- Provide photoprotection - absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen, forming reactive oxidant molecules that are dangerous to the cell.
- Have a photoprotective role in the human eye.
- AKA: phytochemical - compounds with anti-oxidant properties
- The afterglow experienced when excited electrons fall back to the ground state, giving off photons/
- Complexes where chlorophyll, organic, and protein molecules are organized
- Composed of a reaction-center surrounded by several light harvesting complexes.
- Two different types due to their association with difference proteins in the thylakoid membrane which affects the electron distribution in the two pigments that accounts for the slight differences in their light-absorbing properties.
Reaction Center
- An organized association of proteins holding a special pair of chlorophyll a molecules
- Surrounded by several light harvesting complexes
Light Harvesting Complexes
- Act as an antenna for the reaction center complex
Primary Electron Acceptor
- A molecule, found in the reaction center complex, that is capable of accepting electrons and becoming reduced.
- the special chlorophyll a molecules uses energy from light to transfer their electrons to the primary electron acceptor (this is the first step of the light reactions and a redox reaction)
Photosystem II (P680)
- AKA: P680 because its special chlorophyll a pigments are best at absorbing light having a wavelength of 680 nm (red part of the spectrum)
Photosystem I (P700)
- AKA P700 because its special chlorophyll a pigments are best at absorbing light having a wavelength of 700 nm (far red part of the spectrum)
Linear Electron Flow
- A flow of electrons through the photosystems and other molecular components build into the thylakoid membrane.
- The key to the energy transformation of light into the synthesis of ATP and NADPH
- Occurs during the light reactions of photosyntehsis
Cyclic Electron Flow
- An alternative path which uses phtosystem I but not photosystem II.
- The electrons cycle back from Fd to the cytochrome complex and from there continue on to a P700 chlorophyll in the PSI reaction center complex.
- There is no production of NADPH and no release of oxygen. There is ATP generation.
Glyceraldehyde 3-phosphate
- The 3 carbon sugar carbohydrate produced directly from three cycles of the calvin cycle (3 molecules of CO2)
Rubisco (aka: RuBP Carboxylase)
- The enzyme that catalyzes the first step of the calvin cycle (catalyzes the attachment of CO2 to RuBP)
- The most abundant protein in chloroplasts and maybe even on earth
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