Organic Chemistry & Gene Therapy
Advanced Review Document: Stereochemistry & CRISPR Applications
Section 1: Stereochemistry & Molecular Analysis
Q1: In a chemical name, what does the prefix (±) signify regarding the optical
activity of a sample?
Q2: When determining Cahn-Ingold-Prelog (CIP) priority for a chiral center
attached to a benzene ring versus a saturated alkyl chain (e.g., a CH-CH3 group),
which path generally takes priority and why?
Q3: Explain the "Ghost Atom" rule in the context of a carbon-carbon double
bond.
Section 2: Biomedical Applications (CRISPR & Sickle Cell)
Q4: Describe the mechanism by which CRISPR gene therapy treats Sickle Cell
Disease by targeting the BCL11A gene.
Q5: Define the term ex vivo gene therapy and explain the process of
"engraftment" after the edited cells are returned to the patient.
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Answer Key
A1: The (±) or racemic symbol indicates a 50/50 mixture of two enantiomers
(dextrorotatory and levorotatory). Because they rotate plane-polarized light in
equal and opposite directions, the mixture is optically inactive.
A2: The path leading to the benzene ring generally takes priority. While both
may start with a carbon attached to (C, C, H), the benzene carbons are treated as
being bonded to "three" carbons due to the double-bond ghost atom rules,
whereas a saturated alkyl carbon is only bonded to two carbons and a hydrogen.
A3: The "Ghost Atom" rule states that atoms involved in double or triple bonds
are treated as being bonded to multiple equivalent atoms. For a C=C bond, each
carbon is treated as being bonded to two carbons. This increases the priority of
unsaturated groups over saturated ones during CIP analysis.
A4: Sickle Cell CRISPR therapy targets the erythroid-specific enhancer of the
BCL11A gene. BCL11A normally acts as a "switch" that turns off fetal hemoglobin
(γ-globin) production after birth. By disrupting this enhancer, BCL11A expression
is lowered in blood cells, allowing the body to produce healthy fetal hemoglobin
which compensates for defective β-globin.
A5: Ex vivo means "outside the living body." In this therapy, stem cells are
removed from the patient, edited in a lab, and then infused back. Engraftment is
the process where these infused stem cells migrate through the blood and
"home in" on the bone marrow, where they settle and begin producing new,
healthy blood cells.
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