BIOCHEMISTRY Question The citric acid cycle evolved from pre-existing metabolic
ID: 519626 • Letter: B
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BIOCHEMISTRY Question
The citric acid cycle evolved from pre-existing metabolic pathways. Evidence includes organisms that do not use the citric acid cycle, but have genes coding for enzymes used in the citric acid cycle. Diagrams of the citric acid cycle and of possible pathways that linked to form the citric acid cycle are shown.
Which of the statements about the evolution of the citric acid cycle are consistent with existing knowledge?
Possible Answers (in a check all that apply fashion):
The citric acid cycle may have originated from two pathways –a reductive pathway and an oxidative pathway.
The citric acid cycle may have evolved from two biosynthetic pathways in early life forms.
Early organisms may have lacked the enzyme -ketoglutarate dehydrogenase.
A reductive citric acid cycle can replenish oxidized cofactors such as NADH.
Although some organisms do not use the citric acid cycle under anaerobic conditions, they use a reductive pathway similar to the citric acid cycle to generate some larger molecules.
use the citric acid cycle, but have genes coding for enzymes used in the citric acid cycle. Map Diagrams of the citric acid cycle and of possible pathways that linked to form the citric acid cycle are shown. COO CH3-C-CoA H20 CH2 acetyl-CoA acetyl-CoA CoA CH HO- C-COO CH2 COO citrate oxaloacetate synthase citrate COO COO CH CH-O NAD malate dehydrogenase citrate CH COO aconitase oxaloacetate malate HO-C COO isocitrate COO H20 isocitrate fumarase NAD COO socitrate H+ dehydrogenase NADH t CO2 malate fumarate HC COO o ketoglutarate ot-ketoglutarate FAD succinate dehydrogenase ketoglutarate NAD dehydrogenase CoA fumarate FAD CEO succinate NADH H1 COO succinyl-CoA COO CO2 synthetase CH2 succinate CH CH2 succinyl-CoA CH GTP CoA GDP P COO Which of the statements about the evolution of the citric acid cycle are consistent with existing knowlege? The citric acid cycle may have originated from two pathways -a reductive pathway and an oxidative pathway. The citric acid cycle may have evolved from two biosynthetic pathways in early life forms.Explanation / Answer
True : The citric acid cycle may have originated from two pathways –a reductive pathway and an oxidative pathway. The citric acid cycle includes a series of oxidation-reduction reactions that result in the oxidation of an acetyl group to two molecules of carbon dioxide. True: The citric acid cycle may have evolved from two biosynthetic pathways in early life forms (linear and cyclic) True: Early organisms may have lacked the enzyme -ketoglutarate dehydrogenase. False: A reductive citric acid cycle can replenish oxidized cofactors such as NADH. Reductive cycle, is reversible cycle and NAD+ replenished during oxaloacetate to malate and alpha ketoglutarate to isocitrate conversion True:Although some organisms do not use the citric acid cycle under anaerobic conditions, they use a reductive pathway similar to the citric acid cycle to generate some larger molecules.
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