Multiple Choice
Which of the following statements best describes the consequence of chirality in organic molecules?
5. Chirality
Chirality
2:48 minutesProblem 80b
Textbook Question
Citrate synthase, one of the enzymes in the series of enzyme-catalyzed reactions known as the citric acid cycle, catalyzes the synthesis of citric acid from oxaloacetic acid and acetyl-CoA. If the synthesis is carried out with acetyl-CoA that contains radioactive carbon (14C) in the indicated position, the isomer shown here is obtained.
b. If the acetyl-CoA used in the synthesis contains 12C instead of 14C, will the product of the reaction be chiral or achiral?
Verified step by step guidance1
Step 1: Understand the reaction mechanism. Citrate synthase catalyzes the reaction between oxaloacetic acid and acetyl-CoA to form citric acid. The acetyl group from acetyl-CoA is added to oxaloacetic acid, forming a new carbon-carbon bond.
Step 2: Analyze the chirality of the product. Chirality arises when a molecule has a carbon atom bonded to four different groups, making it asymmetric. In the case of citric acid, the chirality depends on the arrangement of substituents around the carbon atoms.
Step 3: Consider the isotopic substitution. If acetyl-CoA contains radioactive carbon (14C), the product will have a labeled carbon atom, which can affect the symmetry of the molecule. However, if acetyl-CoA contains 12C instead of 14C, the molecule's symmetry remains unchanged.
Step 4: Evaluate the symmetry of the product. Citric acid is inherently achiral because it has a plane of symmetry. The substitution of 12C does not introduce asymmetry, so the product remains achiral.
Step 5: Conclude the chirality of the product. When acetyl-CoA contains 12C, the product of the reaction will be achiral, as the molecule retains its symmetry and does not have any asymmetric carbon centers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chirality
Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image, much like left and right hands. A chiral molecule typically has at least one carbon atom bonded to four different substituents, resulting in two distinct enantiomers. Understanding chirality is crucial in organic chemistry, especially in the context of biological systems where the activity of molecules can differ significantly between enantiomers.
Acetyl-CoA
Acetyl-CoA is a central metabolite in cellular metabolism, serving as a key substrate in the citric acid cycle. It is formed from the breakdown of carbohydrates, fats, and proteins and is essential for the synthesis of fatty acids and the production of energy. The presence of isotopes like 14C in acetyl-CoA can be used in tracing experiments to study metabolic pathways and the fate of carbon atoms in biochemical reactions.
Isomerism
Isomerism is the phenomenon where two or more compounds have the same molecular formula but different structural arrangements or spatial orientations. In organic chemistry, isomers can be classified as structural isomers, which differ in the connectivity of atoms, or stereoisomers, which differ in the orientation of atoms in space. The question of whether the product is chiral or achiral relates to the type of isomerism present in the synthesized compound, particularly in the context of the arrangement of substituents around chiral centers.
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