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Unformatted text preview: s more apparent when plants are grown in warm climate. To reduce this
waste, some plants have evolved to carry out C4 photosynthesis in which two
neighboring plant cells collaborate in 1) concentrating CO2 by one cell, and
2) carrying out conventional Calvin cycle CO2 fixation in another cell. The
first cell uses another enzyme, PEP carboxylase, to convert CO2 and a C3
compound, PEP, to form a C4 compound that is then transported to the
second cell where C4 is converted back to C3 , releasing CO2. This efficient
CO2 concentrating mechanism allows the second cell to accumulate enough
CO2 for rubisco to function as a carboxylase and for the conventional Calvin
cycle to take place (see diagram below). 7 11. In which sub-mitochondrial compartment do you expect to find enzymes for TCA
(citric acid) cycle, pyruvate dehydrogenase, β-oxidation of fatty acid, high [H+],
TCA (citric acid) cycle, pyruvae dehydrogenase, and β -oxidation and DNA
are in matrix, the inner most compartment in mitochondria.
High [H+] is present in the intermembrane space between outer and inner
membranes. 12. Why can’t animals convert fats to sugars while plants can?
The bulk of fats are triacylglycerides that can be hydrolyzed to glycerol and
fatty acids. Glycerol can easily enter glycolysis after one step of oxidation (to
glyceraldehyde), and fatty acids have to be degraded to acetyl CoA first.
Acetyl CoA can enter TCA cycle to be oxidized to CO2 and the process
generates a lot of energy, but no net gain of C atoms. Thus, animals cannot
covert acetyl CoA (derived from fatty acid degradation) to sugars. In plants
and some microorganisms, a different pathway, the glyoxylate pathway,
allows acetyl CoA to be condensed with OAA (C4) to form the C6 citrate,
which then bypasses the two CO2 generating steps, and is converted to a C4
intermediate and the C2 glyoxylate. Glyoxylate is then condensed to form a
C4 compound that is eventually converted to the C4 OAA. The output of this
glyoxylate cycle, a C4 compound, is then converted to sugar via
gluconeogenesis. 8 13. Determine the p...
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