Download PPoint Lec 5

Light reactions in
higher plantselectron
carriers and proton
movement, which
makes ATP-sound
familiar?
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PhotorespirationCompeting against photosynthesis-liberates CO2 instead of
fixing it into a 3-carbon moleculeAll Rubisco’s do it
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Xerophytic plants- (can withstand hot, dry conditions) have
modification that allows concentration of CO2
Normally hot weather causes plants to close stomata, which
lowers internal [CO2], which
favors photorespiration
because of Km
of RUBISCO
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C4 photosynthesis called C4 because it starts with 4 carbon
molecules, instead of ‘regular’ photosynthesis which starts with
3 carbon molecules (at least, those are among the first isolated)
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As much as 50% of CO2 fixed by rubisco is reoxidized to
CO2 by photorespiration in C3 plants
-high O2 concentration in atmosphere
C4 plants phosphoenolpyruvate carboxylase has higher
affinity (lower Km) for CO2 than does rubiscoresult can be 2-3 fold greater photosynthetic production
in C4 plants than in C3 plants
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catalytic domain of
RUBISCO
What was first
photosynthetic organism?
Carl Bauer’s lab, Indiana
Univ.-looked at >100 genes
involved in
photosynthesis, then did
phylogenetic analysis to find
out which
most ancient. Purple bacteria
probably first group of
organisms
that were photosynthetic, not
green algae.