9-Photosynthesis-STUDENTVERSION-2

Occur during the calvin cycle cycle must occur 3x to

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Unformatted text preview: • Series of steps which utilize ATP to rearrange 5 molecules of G3P to regenerate 3 molecules of RuBP release of oxygen does not occur during the calvin cycle • Cycle must occur _3x to produce 1 __ net G3P (Fixing 3 CO2) Possibly the most abundant protein on Earth – Technically produces 6 G3P molecules but 5 must be used to regenerate RuBP • For 1 G3P, cycle uses 9 ATP and 6 NADPH 7 1/3/2013 Trouble with Rubisco O2 Rubisco • _______ can fix ___ in place of CO2 – O2 added to Calvin Cycle instead of CO2 creating a 2-carbon compound that is broken down by mitochondria and peroxisomes to release CO2 – Consumes ATP and decreases photosynthesis by siphoning off material from the Calvin Cycle Photorespiration decreases efficiency of the plant • Problem in hot dry climates – Plants close stomata to minimize H2O loss but this reduces the amount of CO2 available – Concentration of O2 released from light reactions increases favoring O2 fixation -- rate of photorespiration will increase which is not good for the plant 8 1/3/2013 Alternative Mechanisms for CO2 Fixation • Plants that use rubisco for initial carbon fixation are called C3 plants – Because first product formed is 3-carbon compound • Some plants have alternative modes of carbon fixation to minimize photorespiration – C4 Plants – CAM (crassulacean acid metabolism) C4 Plants • Carbon fixation is separated _SPATIALLY ________ from the Calvin cycle – CO2 is initially fixed by PEP carboxylase _____________ in mesophyll cells to form a 4-carbon product – Product is transported into bundle sheath cells where the CO2 is released and...
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This note was uploaded on 01/14/2014 for the course BIO 1113 taught by Professor Rothacker during the Winter '12 term at Ohio State.

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