Old Test 4

Question 1

Binding of hormone to a receptor tyrosine kinase causes all of the following EXCEPT:

4

Answer 1

b. hydrolysis of GTP bound to Ras

Question 2

Which statement is NOT true about the role of adapter proteins in the activation of Ras by receptor tyrosine kinases?

8

Answer 2

Sos acts as a GAP, which helps convert Ras·GDP to active Ras·GTP

Question 3

1,2-diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) are cleaved from phosphatidylinositol 4,5- bisphosphate (PIP2) by the enzyme:

9

Answer 3

a. phospholipase C

Question 4

Which of the following mechanisms can terminate an intracellular signaling pathway once the concentration of an external signal decreases?

15

Answer 4

a.degradation of the second messenger
b. deactivation of a signal transduction protein
c. desensitization of receptors

all three

Question 5

DAG activates:

18

Answer 5

PKC

Question 6

How can multiple MAP kinase pathways be segregated when they share a common component, like a downstream kinase?

20

Answer 6

formation of pathway-specific complexes assembled on molecular scaffolds

Question 7

Cholera toxin can make you sick through overactivation of a Gsα pathway even if your body stops making the ligand associated with activation of the pathway. Knowing this, which statement CANNOT be true about cholera toxin?

24

Answer 7

Cholera toxin activates a ligand-activated G protein-coupled receptor

Question 8

Of the components of a heterotrimeric G protein, which subunit is able to activate downstream responses?

29

Answer 8

ALL Three

a, y, and B

Question 9

What is meant by signal transduction?

2

Answer 9

Intracellular signaling pathways that convert an extracellular stimulus (received signal) into a series of chemical and protein interactions that mediate a cellular response.

Question 10

No matter how the signal initiated by the binding of a ligand is transmitted (via a second messenger or by protein recruitment), what is the outcome of that signal?

3

Answer 10

A protein at the top of an intracellular signaling pathway is activated

Question 11

Which statement below is an accurate description of receptor-mediated dimerization?

13

Answer 11

Ligands act as allosteric regulators that turn on the ability of their receptors to form dimers.

Question 12

What allows receptors for extracellular signaling molecules present on the responding cell’s surface to recognize such molecules so readily?

22

Answer 12

They bind the signaling molecules with high affinity.

Question 13

Once the kinase domain of receptor protein-tyrosine kinase has been activated, what does the activated receptor protein-tyrosine kinase do?

38

Answer 13

each receptor subunit phosphorylates its partner on tyrosine residues found in regions adjacent to the kinase domain.

Question 14

Why does calcium not bind to calmodulin in an nonstimulated cell?

39

Answer 14

Calmodulin’s affinity for calcium ions is too low to allow binding in an nonstimulated cell.

Question 15

Cell sensitivity to an external signal is determined by

5

Answer 15

the number of surface receptors

Question 16

Which of the following general statement(s) about a G protein-coupled receptor is (are) true?

Answer 16

It contains seven transmembrane domains.
It is organized with the C-terminus on the cytoplasmic face of the membrane.