Module 3: Lesson 4

Question 1

What types of proteins to GTP-binding proteins exist as?

Answer 1

Monomeric or trimeric proteins.

Question 2

The largest class of molecular switches are governed by…

Answer 2

phosphorylation status.

Question 3

What are the main types of enzyme-coupled receptors?

Answer 3

Receptor tyrosine kinases (RTKs), tyrosine kinase-associated receptors, and receptor serine/threonine kinases.

Question 4

What is the function of receptor tyrosine kinases (RTKs)?

Answer 4

RTKs are binding growth factors, cytoplasmic domains have intrinsic enzymatic activity, phosphorylate themselves, recruit and phosphorylate various intracellular signaling proteins and initiate numerous signaling pathways. They also make up the majority of enzyme-linked receptors.

Question 5

What is the function of tyrosine kinase-associate receptors?

Answer 5

They act through cytoplasmic tyrosine kinases, and do not have a tyrosine kinase domain. Example: cytokine receptors.

Question 6

What is the function of receptor serine/threonine kinases?

Answer 6

They specifically phosphorylate the hydroxyl side chains of serine or threonine amino acid residues. Example: bind members of the TGFb superfamily.

Question 7

How are RTK responses caused and terminated?

Answer 7

Receptors make contact and undergo conformational changes that activates kinase activity via cross-phosphorylation. The responses are terminated via protein tyrosine phosphotases.