Powering Life: Capturing Light to Build Carbohydrates Flashcards

Question

electron transport chain reaction centre

Answer 1

Reaction centre: where light energy is converted into chemical energy as a result of excited electron’s transfer to adjacent molecules. Directly involved in electron transport Antenna chlorophylls transfer energy to the reaction centre - make the chain more efficient When excited, reaction centres transfer an electron to an adjacent molecule that acts as an electron acceptor Reaction centre is oxidised Adjacent molecule is reduced Chain of redox reactions results in NADPH Reaction centre must gain an electron to absorb light again

Answer 2

``` Abundant in cells O2 is created from removing electrons O2 diffuses easily Lots of energy to pull electrons from it Require two photosystems - first gives energy to remove electrons from water, the second allows electrons to be transferred to NADP+ Split to make H+ and O2 (on lumen side) ```

Answer 3

Large increase of energy as electrons pass through two photosystems At every other step there is a slight decrease in energy - exergonic reactions and so electrons move in one direction through the redox reactions (would require an input of energy to go other way) Photosynthetic electron transport chain is called Z scheme sometimes (up and down in energy)

Answer 4

Supplies electrons to the beginning of the electron transport chain It is oxidised and able to pull electrons from water Not a strong enough reductant to reductant to form NADPH Enzyme that pulls electrons from water is located on lumen side of II

Answer 5

Energises electrons with a second input of energy so they can reduce NADP+ Not a strong enough oxidant to split water NADPH is formed when electrons are passed from I to a membrane associated protein called ferredoxin (Fd) Enzyme ferredoxin-NADP+ reductase catalyses the formation of NADPH by transferring two electrons from two molecules of reduced ferredoxin to NAPD+ as well as a proton from the surrounding solution NADP+ +2e- + H+ ——> NADPH

Answer 6

Include two photosystems Cytochrome-b6 f complex (cyt) - electrons pass through it between photosystem II and I Plastoquinone (Pq) - lipid soluble, carries electrons from II to cyt by diffusing through the membrane Plastocyanin (Pc) - water-soluble protein, carries electrons from cyt to I by diffusing through thylakoid lumen

Answer 7

Synthesis of ATP: Synthesised by ATP synthase - transmembrane protein powered by a proton gradient from the lumen to the stroma Oxidation of water releases proteins into the lumen Cyt and Pq function as a proton pump together that is functionally and evolutionarily related to proton pumping in cellular respiration Steps: Transport of two electrons and two protons by diffusion of Pq from the stroma of II to the lumen of cyt Transfer of electrons within cyt to a different molecule of Pq which results in more protons coming from the stroma to the lumen Concentration of protons is 1000x greater in lumen than stroma (3 pH units difference) Accumulation is used to power the synthesis of ATP by oxidative phosphorylation

Answer 8

Four electrons transported in the photosynthetic electron transport chain (reduce NADP+) does not transport enough protons into the lumen to produce three ATP Another pathway for electrons is needed Cyclic electron transport: electrons from photosystem I are redirected from ferredoxin back into the electron transport chain by Pq. Electrons eventually return to I - pathway is cyclic in contrast to linear movement of electrons from water to NADPH As electrons are picked up by Pq, protons are taken in from the stroma to the lumen and are used to synthesis ATP

Answer 9

New source of energy | Released oxygen into the atmosphere

Answer 10

UV damages DNA and other macromolecules Earliest interaction may have been evolution of UV-absorbing compounds Mutations lead to variants that may have been able to transfer electrons like a reaction centre Could not have used chlorophyll because it is a complex pathway of at least 17 steps Intermediate compounds leading to chlorophyll may have been used Early reaction centres: Use light energy to move electrons from an electron donor outside the cell to an electron-acceptor within the cell Synthesise carbohydrates First electron donor might have been Fe2+ which was in the ocean May have been cyclic and not needed a donor Light driven electron transport could have been coupled with movement of protons across the membrane allowing for the synthesis of ATP

Answer 11

Ancient forms had one photosystem - not enough to split water Must have oxidised things like H2S - must live in such environments and do not produce O2 Cyanobacteria were first to evolve ability to use water - two photosystems in a single photosynthetic electron transport chain Genetic material associated with with one photosystem might have been transferred to a bacterium that already had a photosystem Or genetic material for photosystems was duplicated and overtime they diverged slightly (duplication and divergence) Photosynthesis could not occur anywhere there was water and sun

Answer 12

Cyanobacterium ingested by a eukaryotic cell and lost ability to survive outside and evolved into a chloroplast Two membranes

Answer 13

Unfolded regions of the plasma membrane (can be called thylakoids) Photosynthetic pigments imbedded in the membranes and organised into one or more photosystems

Answer 14

Plants and cyanobacteria H2O is split and supplies the electron to the reaction centre Oxygen is realised as a byproduct

Answer 15

Bacterial phototrophs Compounds other than water are used as electron donors such as hydrogen sulphide or thiosulfate Does not produce oxygen

Answer 16

Photosynthetic organisms produced so much oxygen and ran out of carbon dioxide Everything nearly died

Answer 17

Electromagnetic energy: kinetic energy (light is a form of electromagnetic energy). Energy is either kinetic or potential Visible light: the part of the spectrum that we can see. Each colour is a different wavelength Violet and blue have the most energy, red and orange have the least

Answer 18

Increased surface area to volume ratio Can accomodate a large amount of light harvesting pigments Large separation between light systems PPT for extra point

Answer 19

Redox reactions Electrons move from PSII to PSI through an electron transport chain Good diagram on the slide

Answer 20

Sunlight Lots of water CO2 Plants have adapted to their environments Optimal temperature and pH for the enzymes

Answer 21

Some wavelengths can’t penetrate as deep Brown, green and red algae are observed There are a range of algal pigments Blue light (lots of energy) gets deepest in water column Micro and macro algae have evolved a range of pigments to absorb light at different depths The colour of the algae is the wavelength it reflects Deepest algae is a red algae which is about 295m but water has to be very clear These organisms are eukaryotes and they all have chlorophyl a (may have some accessory pigments too)

Answer 22

Mariana trenches with black smokers Yes - anoxygenic photosynthesis in bacteria Does not produce oxygen Hydrogen sulphide can be the electron donor

Answer 23

2391m H2S or elemental sulphur, no oxygen, CO2 and light Geothermal light (not visible) Contain bacteria chlorophylls and carotenoid pigments

Answer 24

DCIP (blue) accepts electrons produced from light reactions and is reduced and made colourless Measure rate at which it loses colour to estimate rate Measure with a spectrophotometer (decrease in absorbance) - do not say absorption

Answer 25

Different wavelengths drive photosynthesis differently Plants use blue and red parts Carotene and some more minor pigments might absorb green lights Chloroplasts reflect most green light and absorb the others