CHEM 2001 Chapter : Problem Set 15KEY

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15 Mar 2019

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In general, the citric acid cycle is inhibited under _high___ (high, low) energy conditions. The carbons that leave as co2 come from oxaloacetate that condensed with acetyl coa. The mandatory sequential binding of the two substrates prevent unwanted side reactions. Oxaloacetate must bind first to create the binding site for acetyl-coa. This ensures that the oxaloacetate is present in the active site when acetyl-coa so they can be condensed together. This prevents acetyl-coa from being alone in the active site where it could be cleaved in a worthless reaction without oxaloacetate: explain how the citric acid cycle is regulated by the energy charge and electron carrier molecules. The citric acid cycle is regulated at the two oxidative decarboxylation steps: isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase complex. When nadh (immediate product) and atp (downstream product) levels are high, these enzymes are inhibited.

Related Questions

Certain bacteria in the genus Chloroflexus as well as certainarchaea are actually capable of splitting malyl-CoA to formacetyl-CoA and glyoxylate. Many of these bacteria require a sourceof organic carbon to grow but have reduced organic carbonrequirements and hence are able to grow in nutrient poorenvironments. These bacteria are also capable of (effectively)synthesizing malyl-CoA from acetyl-CoA and carbon dioxide.
A) Would you expect these bacteria to be capable of a netconversion of carbon from fat to carbon in sugar? Why or why not?What cycle do these bacteria likely to possess that plants alsohave but animals apparently lack?

B) Would you expect that the citric acid cycle is active when thesebacteria fix carbon or do you expect key steps of the citric acidcycle to be inoperable when these bacteria fix carbon? Explain youranswer.

C) What molecule do you expect would signal that the citric acidcycle no longer is useful to the bacterium and that it isappropriate to switch off the citric acid cycle? What does anaccumulation of this molecule mean in terms of whether thebacterium is in an aerobic or anaerobic environment? Whichenzyme(s) in the citric acid cycle are âturned offâ by thismolecule, e.g. under anaerobic conditions? Do the Chloroflexusspecies in question ever fix carbon under aerobic conditions?

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1. If the keto carbon atom (#2) of pyruvate were to be labeled with ¹⁴C , which of the carbon atom(s) of oxaloacetate would be labeled at the end of one turn of the citric acid cycle? (numbering similar to sugars with #1 the carboxylic acid carbon, #2 the keto group, #3 the methyl group) [Ogstonâs symmetry argument was that citric acid exhibited chirality when it bound to enzyme explaining why neither carbon of acetylCoA came off as CO₂ in the first turn of the cycleâthe same chirality argument does not hold for succinate because it is symmetrical about a bond]

a) None. The label will be lost in CO₂.

b) #1 carbon

c) #2 carbon

d) #3 carbon

e) #4 carbon

f) the #2 and #3 carbons will be labeled

g) the #1 and #4 carbons will be labeled

2. If acetyl-CoA is labeled at the methyl carbon (#2) with ¹⁴C, how many turns of the citric acid cycle (starting at the formation of Citrate) will be required to first release some labeled CO₂ ?

a) less than one complete turn

b) one complete turn (back to citrate)

c) more than one, but less than two complete turns

d) only after two complete turns

3. How many ATP or equivalents would be generated from the Succinyl-CoA step after the equivalent of all its four carbons (donât worry about position) were converted to CO₂? State your assumptions, e.g. ample AcCoA is present.

CHEM 2001 Chapter : Problem Set 15KEY

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