Question

1. Ras nucleotide exchange is stimulated by ___.
2. A mutation in RTK receptor that allows the receptor to bind the ligand and pair with a wild-type receptor but blocks signal transduction is classified as a ________ ________ mutation, whereas a mutation that activates RTK pairing signal transduction even in the absence of ligand is classified as a ______________ _______ mutation.
3. PTEN is a phosphatase that removes a phosphate group from ____, thereby preventing its activation of Akt kinase.

Answer 1

1. Ras nucleotide exchange is stimulated by GPCR/EGF receptor and SOS

Explanation:

Son of Sevenless (SOS) is a Guanine nucleotide exchange factor (GEF) and exchanges GDP for GTP.

2. A mutation in RTK receptor that allows the receptor to bind the ligand and pair with a wild-type receptor but blocks signal transduction is classified as a _____dominant negative________ mutation, whereas a mutation that activates RTK pairing signal transduction even in the absence of ligand is classified as a _____constitutively active_________ mutation.

Explanation:

Dominant negative mutations produce altered protein which acts opposite to that of the wild type.

When a receptor is constitutively active, it is functional and generated signal/second messenger even in the absence of a ligand.

3. PTEN is a phosphatase that removes a phosphate group from __PIP3__, thereby preventing its activation of Akt kinase.

Explanation:

PTEN is a tumor suppressor protein which converts PIP3 to PIP2. This reduces Akt's binding ability to membrane, thereby reducing its activity.