Multiple choice

Which of the following statements is incorrect as far as G-protein mediated signal transduction is concerned?

  1. G-proteins have intrinsic GTPase activity.

  2. Activated G-protein transmits signals by binding to other proteins.

  3. G-protein exists as GDP and GTP-bound forms.

  4. The 7TM receptors are coupled to G-proteins.

  5. G-proteins are structurally and functionally similar.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This is not true because different G-proteins exist. There are some thousand heteromeric G proteins as the human genome possesses in excess of 15 genes for the alpha subunits, more than 5 genes for beta subunit and nearly 10 encoding the gama subunits. For example, G-alphaS stimulates adenylate cyclase, G-alpha i inhibits adenylate cyclase. This shows that all the G-proteins are not similar.

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