The activity of retinoblastoma protein (Rb) is regulated primarily by phosphorylation at various serine/threonine residues. Specific...

The activity of retinoblastoma protein (Rb) is regulated primarily by phosphorylation at various serine/threonine residues. Specific patterns of pRb phosphorylation generate pRb conformational variants that mediate distinct protein-protein interactions. In an experimental cell system with a mutation in the Rb gene that encodes alanine rather than serine, which is phosphorylated in the wild-type Rb, you observe that the cell is unable to enter into the cell cycle. What this observation suggest and how do you design an experiment to substantiate your suggestion?

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Expert Solution

1. Retroblastoma gene is abdicated as Rb and it's protein is abdicated as Rbp ( retinoblastoma protein-given as pRb) .

Note: Retinoblastoma gene is a tumor suppressor and it's function is to prevent excessive cell growth by inhibiting the cell cycle progression until cell is ready to divide & Rb is able to regulate apotosis directly at mitochondria in a non transcriptional way by interaction with pro- apoptotic protein (Bax). When cell is ready to divide then retinoblastoma undergoes phosphorylation to form retinoblastoma protein (pRb) which inactivates the Retinoblastoma (Rb) which allows cell to enter cell cycle.

When retinoblastoma is mutated then it will effect cell cycle progression ,cell proliferation, differentiation leading to increased cell proliferation (or) increased cell death.

Given that place of serine is replaced by alanine- alanine blocks phosphorylation of the retinoblastoma and the retinoblastoma protein can't form,

*so pRb is not formed & will not inactivate Rb leading to inability of cell to enter cell cycle.

& association with Bax is affected by alanine mutation.

2. a)Immunoprecipitation of retinoblastoma with Bax antibodies can help in expression of mutation in retinoblastoma protein ( pRb).This is by receprocal co- immunoprecipitation experiments.

b)George Beadle & Edward Tatum experiment says that genes are responsible for giving directions to produce enzyme that controls metabolism i.e; the one gene,one enzyme concept- if a gene is mutated then enzyme from that gene can get effected.

gladiator answered 1 year ago

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