Short answer 1 what technique was used to demonstrate

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SHORT ANSWER 1. What technique was used to demonstrate that gene expression of the CO 2 -concentrating mechanism (CCM) transporters is induced by low levels of CO 2 ? Briefly explain the basis of the technique. ANS: The technique used was reverse transcriptase PCR (RT-PCR). In this technique, mRNA is isolated from cell populations before and after CO 2 limitation. Using reverse transcriptase, the transcripts are converted to complementary DNA (cDNA), which is then amplified by PCR to generate enough DNA to visualize through simpler techniques, such as gel electrophoresis and Northern blotting. The amounts of product are compared under each condition to see if induction occurred. DIF: Medium REF: 15.2 TOP: II.C.i.a MSC: Understanding 2. It is thought that the Calvin cycle appeared after the divergence of the three domains of life. What supports this hypothesis? ANS: The full Calvin cycle is only found in bacteria and organelles of bacterial origin. It is not found in archaea or the cytoplasm of eukaryotes. Also, the uniformity of the pathway across species, as opposed to the diversity of anaerobic pathways of carbon dioxide fixation, supports the hypothesis of late emergence. DIF: Difficult REF: 15.2 TOP: II.A.ii MSC: Analyzing 3. What techniques and technical advances allowed Melvin Calvin to study carbon fixation? Why did he choose the unicellular alga Chlorella ? ANS: Melvin Calvin and his group used 14 C, which has a long half-life. Although found in nature, 14 C is not abundant and has to be produced in special facilities to be used in labeling of molecules for biological experiments. With the availability of 14 C-labeled substrates to investigate CO 2 fixation, Calvin used two-dimensional paper chromatography to separate the metabolites synthesized promptly after exposure of photosynthetic cells to [ 14 C]-HCO . Using a unicellular organism that is easy to culture and harvest by centrifugation ensured the capture of the photosynthetic intermediates shortly after a pulse of [ 14 C]-HCO and alcohol extraction. DIF: Medium REF: 15.2 TOP: II.B MSC: Analyzing 4. How does the reductive or reverse TCA cycle differ from the regular TCA cycle? ANS: Most of the individual reactions of the TCA cycle are reversible, allowing the cycle to fix CO 2 and to generate acetyl-CoA, instead of consuming it. Acetyl-CoA can proceed to gluconeogenesis via pyruvate; its acetyl moiety can enter diverse anabolic pathways. The three enzymes that are particular to the reverse TCA cycle are: ATP-citrate lyase, which breaks down citrate to oxaloacetate and acetyl-
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