Harper’s Illustrated Biochemistry, 29th Edition (2012)
SECTION V. Biochemistry of Extracellular & Intracellular Communication
Exam Questions
Section V
1. Regarding membrane lipids, select the one FALSE answer.
A. The major phospholipid by mass in human membranes is generally phosphatidylcholine.
B. Glycolipids are located on the inner and outer leaflets of the plasma membrane.
C. Phosphatidic acid is a precursor of phosphatidylserine, but not of sphingomyelin.
D. Phosphatidylcholine and phosphatidylethanolamine are located primarily on the outer leaflet of the plasma membrane.
E. The flip-flop of phospholipids in membranes is very slow.
2. Regarding membrane proteins, select the one FALSE answer.
A. Because of steric considerations, alpha-helices cannot exist in membranes.
B. A hydropathy plot helps one to estimate whether a segment of a protein is predominantly hydrophobic or hydrophilic.
C. Certain proteins are anchored to the outer leaflet of plasma membranes via glycophosphatidylinositol (GPI) structures.
D. Adenylyl cyclase is a marker enzyme for the plasma membrane.
E. Myelin has a very high content of lipid compared with protein.
3. Regarding membrane transport, select the one FALSE statement.
A. Potassium has a lower charge density than sodium and tends to move more quickly through membranes than does sodium.
B. The flow of ions through ion channels is an example of passive transport.
C. Facilitated diffusion requires a protein transporter.
D. Inhibition of the Na+ K+-ATPase will inhibit sodium-dependent uptake of glucose in intestinal cells.
E. Insulin, by recruiting glucose transporters to the plasma membrane, increases uptake of glucose in fat cells but not in muscle.
4. Regarding the Na+ K+-ATPase, select the one FALSE statement.
A. Its action maintains the high intracellular concentration of sodium compared with potassium.
B. It can use as much as 30% of the total ATP expenditure of a cell.
C. It is inhibited by digitalis, a drug that is useful in certain cardiac conditions.
D. It is located in the plasma membrane of cells.
E. Phosphorylation is involved in its mechanism of action, leading to its classification as a P-type ATP-driven active transporter.
5. What molecules enable cells to respond to a specific extracellular signaling molecule?
A. Specific receptor carbohydrates localized to the inner plasma membrane surface.
B. Plasma lipid bilayer.
C. Ion channels.
D. Receptors that specifically recognize and bind that particular messenger molecule.
E. Intact nuclear membranes.
6. Indicate the term generally applied to the extracellular messenger molecules that bind to transmembrane receptor proteins:
A. Competitive inhibitor
B. Ligand
C. Scatchard curve
D. Substrate
E. Key
7. In autocrine signaling
A. Messenger molecules reach their target cells via passage through bloodstream.
B. Messenger molecules travel only short distances through the extracellular space to cells that are in close proximity to the cell that is generating the message.
C. The cell producing the messenger expresses receptors on its surface that can respond to that messenger.
D. The messenger molecules are usually rapidly degraded and hence can only work over short distances.
8. Regardless of how a signal is initiated, the ligand-binding event is propagated via second messengers or protein recruitment. What is the ultimate outcome of these binding events?
A. A protein in the middle of an intracellular signaling pathway is activated.
B. A protein at the top of an intracellular signaling pathway is activated.
C. A protein at the top of an extracellular signaling pathway is activated.
D. A protein at the top of an intracellular signaling pathway is deactivated.
E. A protein at the bottom of an intracellular signaling pathway is activated.
9. What features of the nuclear receptor superfamily suggest that these proteins have evolved from a common ancestor?
A. They all bind the same ligand with high affinity.
B. They all function within the nucleus.
C. They are all subject to regulatory phosphorylation.
D. They all contain regions of high amino acid sequence similarity/identity.
E. They all bind DNA.
10. What effect does degradation of receptor-ligand complexes after internalization have upon the ability of a cell to respond if immediately re-exposed to the same hormone?
A. The cellular response is attenuated due to a decrease in cellular receptor number.
B. Cellular response is enhanced due to reduced receptor-ligand competition.
C. The cellular response is unchanged to subsequent stimuli.
D. Cell hormone response is now bimodal; enhanced for a short time and then blunted.
11. Typically, what is the first reaction after most receptor protein-tyrosine kinases (RTKs) bind their ligand?
A. Receptor trimerization
B. Receptor degradation
C. Receptor denaturation
D. Receptor dissociation
E. Receptor dimerization
12. Where is the kinase catalytic domain of the receptor protein-tyrosine kinases found?
A. On the extracellular surface of the receptor, immediately adjacent to the ligand binding domain.
B. On an independent protein that rapidly binds the receptor upon ligand binding.
C. On the cytoplasmic domain of the receptor.
D. Within the transmembrane spanning portion of the receptor.
13. The subunits of the heterotrimeric G proteins are called the _____, _____ and _____ subunits.
A. α, β, and χ
B. α, β, and δ
C. α, γ, and δ
D. α, β, and γ
E. γ, δ, and η
14. Of the receptors listed below, which can conduct a flow of ions across the plasma membrane when bound to their cognate ligand?
A. Receptor Tyrosine Kinases (RTKs).
B. G-protein coupled receptors (GPCRs).
C. G protein coupled receptors
D. Steroid hormone receptors
E. Ligand-gated channels
15. Which of the following is NOT a natural ligand that binds to G-protein coupled receptors?
A. Hormones
B. Steroid hormones
C. Chemoattractants
D. Opium derivatives
E. Neurotransmitters
16. Place the events of signaling listed below in the CORRECT order.
1. G protein binds to activated receptor forming a receptor-G protein complex.
2. Release of GDP by the G protein.
3. Change in conformation of the cytoplasmic loops of the receptor.
4. Binding of GTP by the G protein.
5. Increase in the affinity of the receptor for a G protein on the cytoplasmic surface of the membrane.
6. Binding of a hormone or neurotransmitter to a G-protein coupled receptor.
7. Conformational shift in the α subunit of the G protein.
A. 6 - 3 - 5 - 1 - 2 - 4 - 7
B. 6 - 5 - 4 - 1 - 7 - 2 - 3
C. 6 - 3 - 5 - 1 - 7 - 2 - 4
D. 6 - 7 - 3 - 5 - 1 - 2 - 4
E. 6 - 3 - 5 - 1 - 7 - 2 - 4
17. Which heterotrimeric G proteins couple receptors to adenylyl cyclase via the activation of GTP-bound Ga subunits?
A. Gr family
B. Gq family
C. Gi family
D. G12/13 family
E. Gs family
18. What must happen in order to prevent overstimulation by a hormone?
A. Hormones must be degraded.
B. G proteins must be recycled and then degraded.
C. Receptors must be blocked from continuing to activate G proteins.
D. Receptors must dimerize.
19. Which of the following hormones termed the “flight-or-fight” hormone is secreted by the adrenal medulla?
A. Epinephrine
B. Oxytocin
C. Insulin
D. Glucagon
E. Somatostatin
20. Which hormone is secreted by α-cells in the pancreas in response to low blood glucose levels?
A. Insulin
B. Glucagon
C. Estradiol
D. Epinephrine
E. Somatostatin
21. In liver cells the expression of genes encoding gluconeogenic enzymes such as phophoenolpyruvate carboxykinase is induced in response to which of the following molecules?
A. cGMP
B. Insulin
C. ATP
D. cAMP
E. Cholesterol
22. What happens to protein kinase A (PKA) following the binding of cAMP?
A. The regulatory subunits of PKA dissociate, thereby activating the catalytic subunits.
B. PKA catalytic subunits then bind to two regulatory subunits, thereby activating the catalytic subunits.
C. The inhibitory regulatory subunits dissociate from the catalytic subunits, completely inactivating the enzyme.
D. The stimulatory regulatory subunits dissociate from the catalytic subunits, inhibiting the enzyme.
E. Phosphodiesterase binds to the catalytic subunits, which results in enzyme inactivation.