Ch21.1 - Review Turn on your CPS clicker if you have one....

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Unformatted text preview: Review Turn on your CPS clicker if you have one. When does photorespiration occur in plants? A. When rubisco uses O 2 as a substrate instead of CO 2 . B. When ATP is needed. C. When the Calvin cycle is turned off. D. When there is no sunlight. Photorespiration-- A side reaction of carbon assimilation with no benefit to the plant. Figure 20-20 Rubisco is not just a carboxylase, but also an oxygenase. The costly fix (salvage of phosphoglycolate): Figure 20-21-Oxygen is consumed and CO 2 is released (i.e. photorespiration), but no energy is generated-R15BP consumed and no CO 2 fixed-ATP and NADH are both consumed to convert 2PG to 3PG Why is this considered an costly fx? Carbon assimilation in C 4 plants Figure 20-23b Key enzyme: phosphoenolpyruvate carboxylase-- no oxygenase activity, lower K m for CO 2 than rubisco CO 2 is fixed into oxaloacetate (4C) Cost: 2 extra high energy phosphate Bonds over C3 plants Starch Synthesis (starch synthase): Figure 20-24 Figure 20-25 Sucrose Synthesis (in the cytosol) DHAP + GAP F16BP Figure 20-35/33 Conversion of stored fatty acids to carbohydrates (germinating seeds) So, animals cant do this, but plants and some microorganisms CAN. Chapter 21 - Lipid Biosynthesis Fatty acid synthesis and regulation Triacylglycerol synthesis Which of the following is true about fatty acid synthase of vertebrates? A. It generates NADPH. B. It has a flexible phosphopantetheine arm. C. It is a complex of seven polypeptides. D. Its principal product is stearate. from Biochemistry 3rd Edition Mathews and Van Holde -Oxidation and Fatty Acid Synthesis Why is malonyl-CoA used in fatty acid synthesis? Ultimately, all carbons in fatty acids are derived from acetyl-CoA Condensing two molecules of acetyl-CoA would be difFcult -- no good leaving group So the cell activates acetyl-CoA for making fatty acid chains Enzyme responsible -- acetyl-CoA carboxylase (forms malonyl-CoA) Acetyl-CoA Carboxylase : activation of acetyl-CoA Acetyl-CoA + ATP + HCO 3 Malonyl-CoA + ADP + P i (Biotin is temporary carrier of carboxylate group) Figure 21-1 Mechanism is similar to that of pyruvate carboxylase The general scheme for making fatty acids: There are two acyl carriers in fatty acid synthase: 1) a Cys -SH group 2) phospho-pantetheine -SH group ACP- acyl carrier Protein (-SH) KS- -ketoacyl- ACP synthase (-SH) Fatty Acid Synthase Seven different enzyme activities! Acyl Carrier Protein Figure 21-4/5 Figure 21-5...
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Ch21.1 - Review Turn on your CPS clicker if you have one....

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