lec 17- photosynthesis I Flashcards
what is in the chloroplast and where do the light reactions take place in them?
the chloroplast has thylakoid membranes that form pancake like stacks called grana, the light reactions take place in and around the thylakoid membrane while the dark reaction/calvin cycle takes place in the stroma
what wavelengths stimulate oxygen production according to Engelmann?
blue and red wavelengths attract cyanobacteria, making oxygen
how does Engelmann’s discovery of the bacteria liking red and blue light (action spectrum) relate to the absorption spectrum of chlorophyll?
the absorption spectrum and action spectrum both overlap, meaning that chlorophyll is the primary pigment in photosynthesis
why do leaves appear green?
cause chlorophyll absorbs red and blue light while the most reflected light is green, hence the coloration
how many genes and proteins does the chloroplast genome have?
100 genes, 3000 proteins, 95% encoded by nuclear genome
where do the chloroplast genes move to?
the nuclear genome inside the cytosol, where they produce proteins (endosymbiotic gene transfer)
what do transit peptides do?
import nuclear encoded proteins into the chloroplasts
how is the transit peptide removed?
it is cleaved off at the end of import
what forms a super complex with one another in the thylakoid membrane?
Light harvesting Complex II (LHCII) and photosystem II
does photosystem I also form a super complex?
No
what are the three complexes in the thylakoid membrane?
LHCII, photosystem II, and photosystem I
what are the pigments inside the three complexes?
chlorophyll A, chlorophyll B, and carotenoids (neoxanthin and violaxanthin)
what are PS I and PS II designed to do?
- harvest many photons in an antenna complex
- transfer energy to a central reaction center
what energy levels do the pigments have highest to lowest?
carotenoids, chlorophyll B, chlorophyll A,, chlorophyll P680
where does all the energy transfer too?
the reaction center
what is the reaction center?
chlorophyll P680
what are carotenoids also known as?
accessory pigments
how are the photons in chlorophyll used in photosynthesis?
chlorophyll absorbs blue and red photons, going from ground to excited state, blue excitation state is reduced to the red state releasing heat in the process, red excitation state is used for photosythesis
what are the steps to photosystem II?
- light excites chlorophyll in PSII
- PSII gives off electron to electron transport chain
- void electron is filled by electron from water oxidation
- water oxidation also generates protons and oxygen
- As plastoquinone (PQ) gains electrons (2), it takes 2 protons from stroma
what are the steps to the cytochrome b6f complex ?
- As PQ passes electrons to cytochrome b6f complex, protons are released in the lumen
- The cytochrome b6f complex passes electrons to plastocyanin, a small copper-containing protein
what are the steps to photosystem I?
- light excites chlorophyll in PS I
- chlorophyll gives off electrons to ferredoxin (Fd)/ ferredoxin NADP reductase (FNR)
- void is filled by electrons from plastocyanin
- FNR reduces NADP+ and H+ to NADPH
what happens in ATP synthase- phosphorylation?
- proton diffuse from lumen to stroma via ATP synthase
- diffusion is down chemical gradient
- energy is used to phosphorylation ADP into ATP in stroma
explain zigzag method and division of labour between PSII and PSI:
PSII:
1. PSII P680 is a strong oxidizer , strong enough to oxidize water, splitting it into oxygen , hydrogen protons and electrons for PSI
2. the released protons stay in the lumen
3. the electron transport chain brings protons into the stroma and provide low energy electrons to PSI P700
4. the proton gradient fuels an ATPase that generates ATP
PSI:
5. When P700 electron is excited, it becomes strong reductant, strong enough to reduce NADP+ to NADPH
what is a high-pressure sodium (HPS) light and what are the drawbacks?
a light used in greenhouses that have many drawbacks because most of the energy is not used due to producing light that is mostly not blue or red and it is energy inefficient
what are the steps taken to determine light recipe for plants?
intensity, R:B ratio, additional wavelengths for best shape and taste, daylength to supress or enhance flowering
