# DBT JRF 2022 — Question 64

Exam: DBT JRF 2022 · Section: B · Topic: Immunology › Antibody Engineering - ScFv · Difficulty: Medium

## Question

Short Chain variable fragments (ScFv) of antibody are composed of:

## Options

- **A.** $V_H$ and $V_L$ domains with $C_H$ domain
- **B.** $V_H$ and $V_L$ domains along with Fc region
- **C.** $V_H$ and $V_L$ domains
- **D.** Only Complementarity Determining Regions

## Answer

Option C

## Explanation

Single-chain Fv (scFv) antibody structure: A single-chain Fv (scFv) antibody fragment consists of: • $V_H$ (variable heavy chain domain) connected by a flexible peptide linker to • $V_L$ (variable light chain domain) • Linker: typically 15 amino acids of (Gly₄Ser)₃ — flexible enough to allow proper domain folding • Molecular weight: ~28 kDa (about 1/6 of full IgG at ~150 kDa) • Retains full antigen-binding capacity (both CDR loops of $V_H$ and $V_L$ contribute to the paratope) Advantages of scFv: • Small size → better tissue penetration • Single gene product → easy to engineer and produce in bacteria • Basis for CAR-T cell constructs and bispecific antibodies Disadvantages: No Fc region → short half-life, no complement activation Answer: scFv = $V_H$ -linker- $V_L$ ; full antigen-binding capacity, ~1/6 the size of IgG.

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