Multiple choice

The ras oncogene contribute to the development of cancers by which of the following?

  1. Coding for an anti-apoptotic protein in the cell.

  2. Coding for an enzyme known as GTPase switch protein, which cannot be turn off in its mutated form.

  3. Coding Ras gene products which are involved in lipid signaling pathways.

  4. Coding for a transcription factor, being synthesised in enormous amount in the body.

  5. Coding for a abbreviated form of a growth factor receptor which is continually active.
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B Correct answer
Explanation

The ras gene codes for a GTPase switch protein, which forms part of a growth factor signalling pathway. Stimulation of this protein via an occupied growth factor receptor causes it to activate by exchanging a molecule of GDP for GTP. The activated ras protein then activates downstream proteins, which ultimately activate transcription factors. Normally the ras signal is self limiting because the protein has intrinsic GTPase activity, so it hydrolyses its bound GTP to GDP, switching the signal off.

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