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Structures of the Citric Acid Cycle definitions

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  • Oxaloacetate
    A four-carbon dicarboxylate with a central ketone, serving as both the starting and ending metabolite of the cycle.
  • Citrate
    A tricarboxylic acid formed by adding an acetate group to oxaloacetate, featuring three carboxylate groups.
  • Isocitrate
    An isomer of citrate with a secondary alcohol at carbon 2, also a tricarboxylic acid.
  • Alpha-Ketoglutarate
    A five-carbon dicarboxylate with a ketone at the alpha position, formed by oxidation of isocitrate.
  • Succinyl CoA
    A four-carbon intermediate lacking a carboxylate at one end, distinguished by a thioester linkage to coenzyme A.
  • Succinate
    A four-carbon dicarboxylate regenerated after removal of coenzyme A from succinyl CoA.
  • Fumarate
    A planar, four-carbon dicarboxylate with a trans-alkene, formed by oxidation of succinate.
  • Malate
    A four-carbon dicarboxylate with a secondary alcohol, produced by hydration of fumarate.
  • Carboxylate Group
    A negatively charged functional group (COO−) present at both ends of most cycle intermediates.
  • Tertiary Alcohol
    A hydroxyl group bonded to a carbon attached to three other carbons, as seen in citrate.
  • Secondary Alcohol
    A hydroxyl group bonded to a carbon attached to two other carbons, as seen in isocitrate and malate.
  • Ketone
    A carbonyl group bonded to two carbons, present at the alpha position in alpha-ketoglutarate and oxaloacetate.
  • Thioester
    A functional group formed by a sulfur atom bonded to a carbonyl, as in the linkage of succinyl CoA.
  • Mnemonic
    A memory aid, such as a phrase, used to recall the sequence of cycle intermediates.
  • Dicarboxylic Acid
    A molecule containing two carboxylate groups, characteristic of most cycle intermediates except citrate and isocitrate.