• Circular Dichroism (CD) Spectroscopy:
• Measures the differential absorption of left- and right-circularly polarized light by chiral chromophores in proteins.
• Far-UV Region ($190\text{--}250\text{ nm}$): Reflects peptide backbone absorption, providing quantitative analysis of protein secondary structure:
• $\alpha$-helices exhibit two characteristic negative minima at $208\text{ nm}$ and $222\text{ nm}$ and a positive peak at $193\text{ nm}$.
• $\beta$-sheets show a negative minimum at $218\text{ nm}$ and a positive peak at $195\text{ nm}$.
• Random coils show a negative band near $195\text{ nm}$.
• Near-UV Region ($250\text{--}320\text{ nm}$): Probes tertiary conformation around aromatic amino acids (Trp, Tyr, Phe).

Correct option: (3) Circular Dichroism Spectroscopy.

• CAR-T Cell Therapy Approval in India:
• In October 2023, India's Central Drugs Standard Control Organisation (CDSCO) approved NexCAR19 (actalycabtagene autoleucel), India's first indigenous chimeric antigen receptor (CAR) T-cell therapy developed by IIT Bombay and ImmunoACT.
• Clinical Indication: Approved for patients with relapsed or refractory B-cell malignancies, specifically B-cell acute lymphoblastic leukemia (B-ALL) and diffuse large B-cell lymphoma (DLBCL), by genetically engineering patient T cells to express a CAR targeting the CD19 surface antigen.

Correct option: (2) Refractory B-cell lymphomas and leukemia.

• HAT Medium Selection Mechanism:
• HAT medium contains Hypoxanthine, Aminopterin, and Thymidine:
• Aminopterin: A potent folate analog that blocks dihydrofolate reductase (DHFR), shutting down de novo synthesis of purines and thymidylate.
• Hypoxanthine & Thymidine: Allow cells to survive via salvage pathways if they possess functional salvage enzymes:
• HGPRT (Hypoxanthine-guanine phosphoribosyltransferase) for purine salvage.
• TK (Thymidine kinase) for pyrimidine salvage.
• In hybridoma generation, parent myeloma cells deficient in HGPRT (or TK) die in HAT medium. Primary spleen cells cannot divide indefinitely in culture. Only hybrid cells, which inherit functional HGPRT/TK from B cells and immortality from myelomas, survive.

Correct option: (1) Thymidine kinase and Hypoxanthine guanosine phosphoribosyl transferase