If the Rb gene phosphorylation is defective, which of the following will happen?
(A) Cell cycle will stop at GI phase (B) Cell cycle will stop at G2 phase (C) The cell cycle will progress and the cell will divide (D) There will be no effect on cell cycle as for Rb gene phosphorylation is not needed
(A) Answer- A. Cell cycle will stop at GI phaseRb is a tumor suppressor gene. It normally arrests cell division at G1-S phase. Phosphorylation of Rb gene allows the cell to divide, hence inhibition of phosphorylation (which is the constitutive scenario for Rb gene) arrests the cell in GI phase.RB (Retinoblastoma) geneLocated on chromosome on 13q14Tumor suppressive pocket protein that binds E2F transcription factors in hypophophorylated stateKey negative regulator of G1/S cell cycle transition . Tumors associated: Retinoblastoma, osteosarcoma, Glioblastoma, small cell carcinoma of lung, CA breast & CA bladderSequence: Go- G1- S- G2 - M