Q.48 Arrange the following events occuring in a JAK/STAT signaling pathway in the correct sequence:

A. Phosphorylation of Tyr residues on receptor by JAK
B. Binding of ligand to receptor
C. Dimerisation of receptor
D. Binding of STAT to phosphorylated Tyr and phosphorylation of STAT by JAK
E. Dimerisation of phosphorylated STAT followed by translocation of STAT dimer to nucleus to modulate
gene-expression.

Choose the correct answer from the options given below:

1. C, B, A, D, E

2. B, C, A, D, E

3. B, A, C, E, D

4. A, B, C, D, E

JAK-STAT Signaling Pathway Sequence

The correct sequence in the JAK/STAT signaling pathway starts with ligand binding, leading to receptor dimerization, JAK-mediated phosphorylation, STAT activation, and nuclear translocation.

Correct Answer

Option 2: B, C, A, D, E

This order accurately reflects the canonical steps: Binding of ligand to receptor (B), Dimerisation of receptor (C), Phosphorylation of Tyr residues on receptor by JAK (A), Binding of STAT to phosphorylated Tyr and phosphorylation of STAT by JAK (D), and Dimerisation of phosphorylated STAT followed by translocation to nucleus (E).

Step-by-Step Pathway

• Ligand Binding (B): Cytokines or growth factors bind to cell-surface receptors, initiating the cascade.

• Receptor Dimerization (C): Ligand binding brings receptor chains together, approximating associated JAK kinases.

• JAK Phosphorylation of Receptor (A): Activated JAKs transphosphorylate tyrosine residues on the receptor’s intracellular domain.

• STAT Recruitment and Phosphorylation (D): Phosphorylated tyrosines on the receptor recruit STATs via SH2 domains; JAK then phosphorylates STATs.

• STAT Dimerization and Nuclear Entry (E): Phosphorylated STATs dimerize, translocate to the nucleus, and regulate gene expression.

Option Analysis