5.6.4 light-independent stage
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where does the light-independent stage happen
stroma of chloroplasts
how is the calvin cycle dependent on the light-dependent stage of photosynthesis
ATP & hydrogen are required to reduce carbon dioxide & synthesise large complex organic molecules
5 steps of the calvin cycle (light-independent stage of photosynthesis)
• carbon dioxide combines with ribulose bisphosphate (RuBP) - catalysed by RuBisCO • RuBP becomes carboxylated forming unstable intermediate 6C compound which immediately breaks down • product is 2 molecules of 3C compound, GP (glycerate-3-phosphate) - carbon dioxide has been fixed • GP reduced, with 2 hydrogens from NADPH (light-dependent stage), to triose phosphate (TP) - energy from ATP (light-dependent stage) used at rate of 2 ATP for every carbon dioxide fixed in stage 3 • in 10 of every 12 TP molecules, atoms rearranged to generate 6 molecules of RuBP - requires phosphate groups (from ATP) - chloroplasts contain low levels of RuBP as constantly converted to GP, but constantly regenerated - remaining 2 of 12 TP are product
how many turns of calvin cycle is necessary to produce 2 molecules of TP to make one molecules of glucose
6
why does calvin cycle only run in daylight
products (ATP & NADPH) from light-dependent stage constantly needed for calvin cycle
uses of triose phosphate (TP)
• some TP molecules synthesise organise compounds, eg: - some glucose converted to sucrose, starch & cellulose - some TP synthesises amino acids, fatty acids & glycerol • rest of TP recycled to regenerate RuBP