Question

7.)In G proteins, which form of the guanyl nucleotide is bound in the unactivated state?

a.) GTP

b.) GDP

c.) GMP

d.) dGTP

e.) None of above

8.)which of the following amino acids can be phophorylated?

a.) tyrosine, serine, theronine

b.) tyrosine, serine, tryptophan

c.) serine, threonine, asparagine

d.) histidine, serine, phenylalanine

e.) tyrosine, methionine, typrtophan

9.) most signal molecules:

a.)easily diffuse through the membrane and bind to a receptor in the cytoplasm

b.) bind to membrane receptors and transmit information across a membrane without traversing the membrane

c.) carry out functions in the nucleus after binding to a receptor in the cell membrane

d.) a and c

e.) a,b, and c

10.)the most common motif found in the membrane-spanning proteins is:

a.) alpha helices of non-polar amino acids that pass through the membrane

b.) alpha helices of charged amino acids that form channels via adhesive hydrogen bonding

c.) a triple helix of alpha helices

d.) none of above

11.)which of the following membranes would be most fluid?

a.) bilayer made of lipids with polyunsaturated 18 carbon-fatty acids

b.) bilayer made of lipids with saturaated 18 carbon fatty acids

c.) bilayer made of lipids with saturated 16 carbon fatty acids

d.) bilayer made of lipids with polyunsaturated 16 carbon fatty acids

e.) all of the above are equally equivalent in fluidity

12.)when secreted in the human body, the hormone glucagon causes rapid glycogen in liver cells. This occurs through a GPCR- signaling pathway. Which of the following is the proper sequence following the steps of the reaction cascade?

1- displacement of GDP with GTP on the a-subunit of G-protein

2- degradation of glycogen

3-dissocation of regulatory subunits that activate protein kinase a

4-phophorylation of glycogen degrading enzyme

5-glucagon binds to specific, transmembrane receptor

6- formation of cyclic- AMP by adenyl Cyclase

a.) 5-1-6-3-4-2

b.) 5-6-1-3-4-2

c.) 5-3-1-6-4-2

d.) 5-1-6-3-2-4

e.) 5-3-1-6-2-4

13.)although ligand binding to 7 membrane receptors intiates a signal transduction pathway tiggering a change in tertiary structre, another class of receptors involves dimerization upon ligand binding. The result of this is that:

a.) the intracellular domains are changed from a conformation having highly organized structre into a little organized structre

b.) intracellular protein kinase domains are brought together and activate one another by cross-phosphorylation

c.) intracellular domains acting as second messengers are cleaved and free to move through the cytoplasm

14.) The GTPase activity of G-proteins is important because:

a.) it provides a method wherby the intial signal can be terminated

b.) the G-proteins are active only when GDP is bound to them.

c.) the phosphate released is an important second messenger

15.)the common feature of 7 transmembrane receptors is:

a.) the ability to respond to similar signals

b.) the homolgy between them allows the to act in an interchangebable pattern

c.) the presence of seven transmembrane helices in their structre

16.)the binding of signal molecule to a membrane receptor often results in a change in the cincentration of another molecule inside the cell. This molecule is refered to as:

a. second messenger

b.) a primary messenger

c.) signal terminator

17.)membrane receptor proteins are often used to transfer information from the cell's enviornment to its interior for what reason?

a.) the molecular signal is not soluble in the interior of the cell.

b.) the signal molecule is transported into the cell by the receptor

c.) the signal molecule is too polar to pass through the cell membrane

18.)in passive transport, the energy driving the movement of materials across a membrane is provided by:

a.) nothing there is no energy requirment by passive transport

b.) the concentraion gradient across the membrane

c.) ATP

19.)at any given temperature, the degree of membrane fludity depends on:

a.) the percentage of lipids that contain choline

b.) the percentage of glycolipids

c.) the percentage of unsaturated fatty acids

Answer 1

7. Option B. GDP

8. A (tyrosine, serine, threonine)

9. B (most of the extracellular signal molecules are hydrophilic and bind to the cell surface receptors of the target cell)

10. A (non-polar amino acids)

11. D (polyunsaturated 16 carbon fatty acids. Lipids with short or unsaturated fatty acyl chains undergo the phase transiton at lower temperatures than lipids with long or saturated chains)

12. A (see the image below)

13. B (intracellular protein kinase domains are brought together and activate one another by cross-phosphorylation)

14. A

15. A

16. A

17. C

18. B

19. C