Florida International University

PCB 2099

Principles of Human Physiology, 5e (Stanfield) Chapter 5 Chemical Messengers

Multiple Choice Questions

1)In chemical communication between cells, a                                  cell secretes a chemical messenger that binds to on the cell.

1. 1. gap : connexons : secretory
   2. secretory : connexons : gap
   3. secretory : connexons : target
   4. target : receptors : secretory
   5. secretory : receptors : target

2. Direct communication between cells in contact with one another is accomplished through

                     .

1. 1. ligands
   2. receptors
   3. gap junctions
   4. paracrine chemical messengers
   5. endocrine hormones

3. Which type of chemical messenger, when released, binds to receptors on the cell that released the chemical messenger?
   1. neurohormone
   2. autocrine
   3. hormone
   4. cytokine
   5. neurotransmitter

4. Which type of chemical messenger is released into the bloodstream by an endocrine gland where it can affect target cells throughout the body?
   1. paracrine
   2. autocrine
   3. hormone
   4. cytokine
   5. neurotransmitter

5. Which type of chemical messenger is released from the axon terminal of a neuron and directly communicates with other cells?
   1. paracrine
   2. autocrine
   3. hormone
   4. cytokine
   5. neurotransmitter

6. Communication across a synapse is initiated by the release of a neurotransmitter from the

                      region of the neuron.

1. 1. postsynaptic
   2. axon terminal
   3. perisynaptic
   4. dendritic
   5. axon hillock

7. Vasopressin (antidiuretic hormone), which is released from the posterior pituitary, is an example of this type of chemical messenger.
   1. cytokine
   2. autocrine
   3. paracrine
   4. neurohormone
   5. neurotransmitter

8. Which of the following classes of chemical messengers moves to the target cell by diffusion?
   1. paracrine only
   2. hormone only
   3. neurotransmitter only
   4. both paracrine and neurotransmitter
   5. both hormone and neurotransmitter

9. Which of the following classes of chemical messengers travels in the bloodstream to the target cell?
   1. paracrine only
   2. hormone only
   3. neurotransmitter only
   4. both paracrine and neurotransmitter
   5. both hormone and neurotransmitter

10. Which of the following chemical messengers is lipophilic?
    1. glutamate
    2. histamine
    3. norepinephrine
    4. prostaglandin
    5. gamma-amino butyric acid

11. Which of the following chemical messengers is lipophilic and is therefore able to cross the cell membrane?
    1. amino acids
    2. amines (excluding thyroid hormone)
    3. peptides
    4. eicosanoids
    5. proteins

12. Histamine acts as a(n)                           in its role in inflammation.
    1. paracrine
    2. autocrine
    3. hormone
    4. neurotransmitter
    5. cytokine

13. Which of the following chemical messengers is NOT derived from an amino acid?
    1. epinephrine
    2. testosterone
    3. histamine
    4. thyroid hormones
    5. serotonin

14. All the messengers function as hormones for which of the following chemical classes?
    1. amines
    2. peptides/proteins
    3. steroids
    4. eicosanoids
    5. amino acids

15. All the messengers function as neurotransmitters for which of the following chemical classes?
    1. amines
    2. peptides/proteins
    3. steroids
    4. eicosanoids
    5. amino acids

16. In order to convert the amino acid glutamate to gamma-amino butyric acid, cells must produce the enzyme                                                  that catalyzes this reaction.
    1. glutamic acid dehydrogenase
    2. glutamate dehydrogenase
    3. glutamic acid hydroxylase
    4. glutamate hydrolase
    5. glutamic acid decarboxylase

17. The body is able to synthesize the amino acids glutamate, aspartate, and glycine from

                     .

1. 1. essential amino acids
   2. the degradation of fatty acids
   3. the degradation of glucose in glycolysis and the Krebs cycle
   4. the glycerol in a triglyceride
   5. cholesterol

18. Cells that secrete dopamine must contain which enzymes?
    1. dopamine β-hydroxylase only
    2. dopa decarboxylase only
    3. tyrosine β-hydroxylase
    4. dopamine β-hydroxylase and dopa decarboxylase only
    5. tyrosine β-hydroxylase and dopa decarboxylase

19. Cells that secrete epinephrine must contain which enzymes?
    1. dopamine β-hydroxylase and dopa decarboxylase only
    2. dopamine β-hydroxylase, tyrosine β-hydroxylase, and dopa decarboxylase only
    3. tyrosine β-hydroxylase and phenylethanolamine N-methyl transferase only
    4. dopamine β-hydroxylase, tyrosine β-hydroxylase, phenylethanolamine N-methyl transferase, and dopa decarboxylase
    5. phenylethanolamine N-methyl transferase and dopa decarboxylase only

20. Catecholamines are derived from what amino acid?
    1. glutamate
    2. tryptophan
    3. tyrosine
    4. histidine
    5. glycine

21. Thyroid hormones are synthesized from what amino acid?
    1. glutamate
    2. tryptophan
    3. tyrosine
    4. histidine
    5. glycine

22. Peptide/protein messengers are translated from ribosomes                         .
    1. free in the cytosol
    2. attached to the rough endoplasmic reticulum
    3. attached to the smooth endoplasmic reticulum
    4. attached to the Golgi apparatus
    5. attached to the nuclear envelope

23. While in the rough endoplasmic reticulum, what is the initial polypeptide formed during protein synthesis called?
    1. exon
    2. peptide
    3. propeptide
    4. prepropeptide
    5. prepeptide

24. Once a steroid hormone is synthesized, it is                            .
    1. immediately capable of diffusing across the membrane
    2. stored in a vesicle until released
    3. bound to albumin until released from the cell
    4. stored in a unique protein structure that maintains steroids in the cell
    5. bound to the mitochondria until released

25. What organelle packages peptide/protein messengers into secretory vesicles?
    1. nucleus
    2. rough endoplasmic reticulum
    3. smooth endoplasmic reticulum
    4. Golgi apparatus
    5. lysosomes

26. Name the enzyme that, when activated, will directly release arachidonic acid from a membrane phospholipid.
    1. Phospholipase A2
    2. Phospholipase C
    3. Phospholipase D
    4. Protein kinase A
    5. Protein kinase C

27. In order to synthesize eicosanoids,                           catalyzes the release of                         from a membrane phospholipid.
    1. phospholipase A2 : cholesterol
    2. phospholipase C : arachidonic acid
    3. phospholipase A2 : arachidonic acid
    4. phospholipase C : cholesterol
    5. phospholipase C : inositol biphosphate

28. An equilibrium exists between a hormone that is bound to a carrier protein and a free hormone such that, as the amount of free hormone increases,                                                        .
    1. the amount of bound hormone will not change
    2. more hormone must be synthesized to directly replace the free hormones
    3. more bound hormone will be released from its carrier proteins
    4. more free hormone will become bound to carrier proteins
    5. cells will be stimulated to secrete more free hormone

29. Lipophilic chemical messengers are poorly soluble in water. However, many of these lipophilic messengers are transported throughout the body. Their transport in blood (water) is facilitated by        .
    1. chylomicrons
    2. lipoproteins
    3. carrier proteins
    4. red blood cells
    5. white blood cells

30. What enzyme catalyzes synthesis of prostaglandins from arachidonic acid?
    1. phospholipase C
    2. phospholipase A2
    3. lipoxygenase
    4. cyclooxygenase
    5. tyrosine β-hydroxylase

31. Androgens are precursor molecules for the synthesis of                            .
    1. estradiol
    2. cortisol
    3. progesterone
    4. aldosterone
    5. cholesterol

32. Progesterone is a precursor for the synthesis of                          .
    1. estradiol
    2. cortisol
    3. testosterone
    4. dehydroepiandrosterone
    5. androstenedione

33. Aspirin decreases inflammation by inhibiting the actions of what enzyme?
    1. phospholipase A2
    2. cyclooxygenase
    3. lipoxygenase
    4. protein kinase A
    5. dopa decarboxylase

34. Hormones that are dissolved in blood typically exhibit a half-life on the order of                                  , whereas hormones that are bound to carrier proteins can remain undegraded for                                              .
    1. seconds : hours
    2. seconds : minutes
    3. minutes : hours
    4. hours : minutes
    5. minutes : seconds

35. The β1 adrenergic receptor has the greatest affinity for what messenger?
    1. norepinephrine
    2. epinephrine and norepinephrine equally
    3. epinephrine
    4. dopamine
    5. serotonin

36. The α1 adrenergic receptor has the greatest affinity for what messenger?
    1. norepinephrine
    2. epinephrine and norepinephrine equally
    3. epinephrine
    4. dopamine
    5. serotonin

37. Which of the following will NOT affect the magnitude of a cell's response to a specific hydrophilic ligand?
    1. ligand concentration
    2. number of receptors
    3. receptor upregulation
    4. affinity of the receptor for the ligand
    5. lipid solubility of the ligand

38. Chronic exposure to a ligand (messenger)                             the receptor population for that chemical messenger on the target cell.
    1. decreases the specificity of
    2. decreases the affinity of
    3. upregulates
    4. downregulates
    5. changes the conformation of

39. Which of the following statements best describes the release of lipophobic messengers?
    1. Lipophobic messengers are stored in vesicles and released by exocytosis in response to a stimulus.
    2. Lipophobic messengers are stored in vesicles and released by simple diffusion in response to a stimulus.
    3. Lipophobic messengers are released immediately upon synthesis by simple diffusion.
    4. Lipophobic messengers are stored in vesicles and released by exocytosis immediately after synthesis.
    5. Lipophobic messengers are stored free in the cytosol and released by simple diffusion in response to a stimulus.

40. Which of the following statements best describes the release of a lipophilic messenger?
    1. Lipophilic messengers are stored in vesicles and released by exocytosis in response to a stimulus.
    2. Lipophilic messengers are stored in vesicles and released by simple diffusion in response to a stimulus.
    3. Lipophilic messengers are released immediately upon synthesis by simple diffusion.
    4. Lipophilic messengers are stored in vesicles and released by exocytosis immediately after synthesis.
    5. Lipophilic messengers are stored free in the cytosol and released by simple diffusion in response to a stimulus.

41. Lipophilic hormones are transported in blood                              and bind to receptors located

                     .

1. 1. dissolved in the plasma : on the plasma membrane of the target cell
   2. dissolved in the plasma : inside the target cell
   3. bound to carrier proteins : on the plasma membrane of the target cell
   4. bound to carrier proteins : inside the target cell
   5. inside red blood cells : inside the target cell

42. What is a molecule that is similar in structure to a messenger and binds with that messenger's receptor to stimulate a response from the target cell called?
    1. blocker
    2. synergist
    3. antagonist
    4. agonist
    5. protagonist

43. Which of the following is a non-steroidal antiinflammatory drug?
    1. aspirin
    2. cortisone
    3. testosterone
    4. prostaglandins
    5. morphine

44. What is the portion of a gene that is capable of being bound by a particular hormone-receptor complex to stimulate alterations in that gene's expression?
    1. nuclear receptor
    2. hormone response element
    3. intron
    4. exon
    5. promoter

45. The affinity of a receptor for its ligand is a measure of                              .
    1. the strength of binding between ligand and receptor
    2. the number of binding sites available for the ligand
    3. the ability of the ligand to permeate the plasma membrane and reach its receptor
    4. the response produced in the target cell when the ligand binds to the receptor
    5. the percent of receptors on a specific target cell with bound ligand

46. Typical responses to                          messengers require a long time to develop because they necessitate transcription of mRNA and translation of that mRNA into a functional protein.
    1. lipophobic
    2. lipophilic
    3. amino acid
    4. protein
    5. peptide

47. Which of the following describes ion channels that are coupled to membrane receptors such that their gating properties (opening and closing) are altered by messenger binding.
    1. Enzyme-linked receptors
    2. G protein-linked channels
    3. Voltage-gated channels
    4. Ligand-gated channels
    5. Potential-gated channels

48. Slow gated channels are identified as such because, once the receptor is bound by the ligand, the receptor must first activate a(n)                                                     prior to the channel opening or closing.
    1. G protein
    2. ion channel
    3. enzyme
    4. RNA polymerase
    5. hormone response element

49. Differences in the rate of activity between fast and slow ligand-gated channels is caused by

                     .

1. 1. ligand selectivity
   2. G protein activity gating the fast channel
   3. ligands gating both channels to the closed state
   4. G protein activity gating the slow channel
   5. ligand affinity

50. Which of the following ions can act as a second messenger?
    1. sodium only
    2. potassium only
    3. calcium only
    4. both sodium and potassium
    5. both sodium and calcium

51. Opening channels for which of the following ions can trigger exocytosis?
    1. sodium
    2. potassium
    3. calcium
    4. chloride
    5. magnesium

52. Which of the following ions binds to calmodulin to ultimately activate a protein kinase?
    1. sodium
    2. potassium
    3. calcium
    4. chloride
    5. magnesium

53. Binding of acetylcholine to a nicotinic cholinergic receptor on skeletal muscle will lead directly to what type of movement across the cell membrane?
    1. rapid influx of Na+ through its channel and no movement of K+
    2. rapid influx of K+ through its channel and no movement of Na+
    3. rapid influx of Na+ and slow outward flux of K+
    4. slow influx of Na+ through its channel and rapid outward flux of K+
    5. fast influx of Na+ and K+ through its channel

54. In its role as a                         , calcium binds to                           forming a complex that activates a protein kinase.
    1. second messenger : a phosphatase
    2. first messenger : a hydrolase
    3. second messenger : calmodulin
    4. first messenger : a protein kinase
    5. third messenger : calmodulin

55. Which of the following statements best describes the function of tyrosine kinase?
    1. It catalyzes the formation of dopamine from L-dopa.
    2. It catalyzes the formation of norepinephrine from dopamine.
    3. It catalyzes the phosphorylation of a protein inside a cell.
    4. It catalyzes the phosphorylation of a protein in the extracellular fluid.
    5. It sequesters calcium in the cytosol.

56. Which of the following is NOT an integral membrane protein?
    1. tyrosine kinase
    2. calmodulin
    3. G proteins
    4. adenylate cyclase
    5. phospholipase C

57. Which of the following enzymes directly covalently modulates a protein?
    1. tyrosine kinase
    2. tyrosine β-hydroxylase
    3. adenylate cyclase
    4. phosphodiesterase
    5. phospholipase C

58. The function of a second messenger system is to                           .
    1. buffer a cells response to a ligand
    2. isolate the response to the inside of a cell
    3. keep calcium involved in these responses
    4. amplify the response of the first messenger
    5. facilitate the process of covalent modification of a protein

59. Which of the following is NOT a process whereby calcium is functionally removed from the cytosol of a cell?
    1. active pumping of calcium across the plasma membrane
    2. sequestration of calcium by proteins within the cytosol
    3. active transport of calcium into the smooth endoplasmic reticulum
    4. sequestration of calcium within the Golgi apparatus
    5. active transport of calcium into the mitochondria

60. In its active form, a G protein will have                              .
    1. the alpha and beta subunit separated from the gamma subunit
    2. the gamma subunit separated from the alpha and beta subunit
    3. the beta subunit separated from the alpha and gamma subunit
    4. the alpha subunit separated from the gamma and beta subunit
    5. the alpha and gamma subunit separated from the beta subunit

61. When the alpha subunit of the G protein is activated, it can stimulate ion channels to do what?
    1. either open or close
    2. open only
    3. close only
    4. alter the ion that travels through the channel
    5. degrade

62. The enzyme that catalyzes synthesis of cAMP is called                                 and is activated by

                     .

1. 1. adenylate cyclase : a Gs protein
   2. adenylate cyclase : a Gi protein
   3. phosphodiesterase : a Gs protein
   4. phosphodiesterase : a Gi protein
   5. phosphoprotein phosphatase : a Gi protein

63. What enzyme is activated by cAMP?
    1. phosphodiesterase
    2. adenylate cyclase
    3. tyrosine kinase
    4. protein kinase A
    5. protein kinase C

64. What type of enzyme removes the phosphate group from a covalently modulated protein?
    1. protein kinase
    2. tyrosine kinase
    3. phosphoprotein phosphatase
    4. phosphodiesterase
    5. phospholipase

65. In order to terminate a cAMP-mediated response, the enzyme                            can be activated to degrade cAMP.
    1. cAMP decarboxylase
    2. cAMP hydrolase
    3. cAMP hydrogenase
    4. cAMP phosphodiesterase
    5. cAMP protein kinase

66. When associated with G protein, guanylate cyclase will activate what enzyme?
    1. protein kinase C
    2. protein kinase G
    3. protein kinase A
    4. phosphodiesterase
    5. phospholipase C

67. Which of the following second messengers, when released by phospholipase C, will directly activate the enzyme protein kinase C?
    1. inositol triphosphate
    2. inositol biphosphate
    3. diacylglycerol
    4. phosphatidylinositol biphosphate
    5. cGMP

68. What molecule, whose synthesis is catalyzed by phospholipase C, triggers the release of calcium from the endoplasmic reticulum?
    1. Inositol triphosphate
    2. Inositol biphosphate
    3. Diacylglycerol
    4. Phosphatidylinositol biphosphate
    5. cGMP

69. Which of the following proteins is directly activated by a G protein?
    1. phospholipase A2
    2. adenylate cyclase
    3. tyrosine kinase
    4. calmodulin
    5. protein kinase G

70. What is phosphatidylinositol-4,5-biphosphate?
    1. a second messenger
    2. a phospholipid in plasma membranes
    3. an enzyme that catalyzes formation of a second messenger
    4. a component of a G protein
    5. an enzyme that catalyzes degradation of a second messenger

71. Which of the following describes the signal transduction mechanism for estrogen, a steroid hormone?
    1. opening of fast ligand-gated channels
    2. activation of enzyme-linked receptor
    3. activation of cAMP second messenger system
    4. opening or closing of fast ligand-gated channels
    5. altering transcription of mRNA

72. Which of the following is a second messenger?
    1. cAMP only
    2. calcium only
    3. inositol triphosphate only
    4. both cAMP and inositol triphosphate
    5. cAMP, calcium, and inositol triphosphate

73. Which of the following statements is true for the nervous system but NOT the endocrine system?
    1. A messenger communicates to target cells by binding to specific receptors.
    2. A messenger is transported in the bloodstream.
    3. There is a special anatomical arrangement between the secretory cell and the target cell.
    4. Communication occurs over long distances.
    5. Effector organs are scattered throughout the body.

74. What part of a neuron releases neurotransmitter by exocytosis?
    1. soma
    2. dendrites
    3. axon hillock
    4. axon terminal
    5. all of the above

1. 1. True/False Questions

1. Lipophobic chemical messengers communicate a message to the target cell by binding to receptors on that cell's membrane.

2. The target cell of a neurotransmitter is the postsynaptic cell.

3. Endocrine glands secrete neurohormones.

4. Tyrosine is one of four amino acids that function directly as chemical messengers.

5. Steroid hormones are produced within cells and stored in vesicles until they are released.

6. The enzyme glutamic acid decarboxylase catalyzes the synthesis of glutamate.

7. All catecholamine-secreting cells synthesize dopamine.

8. Eicosanoids are released immediately upon synthesis.

9. Albumin is a peptide hormone.

10. A single cell can have receptors for different messengers.

11. Most receptors are relatively non-specific for the ligand that will bind to them.

12. Receptors for lipophilic chemical messengers are only located on the surface of a cell's membrane.

13. Tyrosine kinases are enzymes that add a phosphate group to tyrosine residues on other proteins, changing the conformation of those proteins.

14. The higher concentration of messenger, the greater the response in the target cell.

15. Enkephalin is an opiate produced in the body. When enkephalin binds to opioid receptors it produces analgesia (a lack of pain sensation). Morphine can also bind to opioid receptors and produce analgesia. Morphine is an opiate antagonist.

16. Thyroid hormones alter the transcription of mRNA in the target cell.

17. If calcium channels open in the plasma membrane, calcium ions enter the cell.

18. An amplifier enzyme catalyzes the synthesis of a second messenger.

19. In its active form, a G protein has a GDP bound to its alpha unit.

20. Generally, the nervous system is a more rapid means of communication than the endocrine system.

21. The site of communication between two neurons is called a synapse.

1. 2. Matching Questions

Match the chemical messenger with its correct description.

1. hormone
2. neurotransmitter
3. paracrine

1. 1. Diffuses to neighboring cells to exert an effect.

1. 2. Released from endocrine glands into the bloodstream.

1. 3. Released by a presynaptic cell.

Match the chemical property to the messenger.

1. lipophilic
2. lipophobic

1. 4. Catecholamines.

1. 5. Peptides/proteins.

1. 6. Steroids.

1. 7. Thyroid hormones.
   8. Eicosanoids.

Match the following enzymes with their functions.

1. tyrosine β-hydroxylase
2. phosphodiesterase
3. adenylate cyclase
4. phospholipase A2
5. tyrosine kinase
6. dopa decarboxylase
7. dopamine β-hydroxylase
8. phosphoprotein phosphatase
1. phospholipase C
10. phenylethanolamine N-methyl transferase
11. cyclooxygenase

1. 9. Catalyzes phosphorylation of a protein.

1. 10. Catalyzes synthesis and release of arachidonic acid.

1. 11. Catalyzes synthesis of epinephrine from norepinephrine.

1. 12. Catalyzes synthesis of cAMP.

1. 13. Catalyzes synthesis of prostaglandins and thromboxanes.

1. 14. Catalyzes dephosphorylation of a protein.

1. 15. Catalyzes synthesis of diacylglycerol and inositol triphosphate.

Match the following properties to the correct communication system.

1. endocrine system
2. nervous system

1. 16. Messenger is a hormone.

1. 17. Quick response time.

1. 18. Target cells limited to neurons, muscles, and glands.

1. 19. Effects tend to be long-lasting.

1. 3. Essay Questions

1. Describe the process whereby a polypeptide chain, which has been translated in the rough endoplasmic reticulum, is converted to an active protein hormone.

2. Describe how chemical messengers are transported to their target tissues.

3. Describe the factors that affect the magnitude of a target cell's response. Assume that there is a receptor on the cell for the ligand.

4. Describe the function of the fast channel-linked receptors, including the role of calcium in their response.

5. Describe G protein-linked receptors, including a discussion of the different enzyme pathways activated by G protein.

1. 4. Short Answer Questions

1. A target cell will respond to a chemical messenger once that molecule has bound to a(n)

                     .

2. A (paracrine / hormone) is transported in the bloodstream.

3. Histamine is an example of a (paracrine / hormone).

4. A neurohormone is (ADH / acetylcholine), which is released from the (kidney / pituitary gland).

5. Lipid soluble molecules are not only hydrophobic, but are also                                .

6. Catecholamines, such as dopamine, norepinephrine, and epinephrine, are derived from the amino acid      .

7. Identify the two enzymes involved in converting tyrosine into dopamine.
8. Eicosanoids are derived from what phospholipid?

9. Steroid messengers are derived from what precursor molecule?

10. Catecholamines are released from the secretory cell by (diffusion / exocytosis).

11. Steroids are released from the secretory cell by (diffusion / exocytosis).

12. Name a protein in the blood that is relatively non-specific with respect to its ability to bind and transport chemical messengers in the blood.

13. As free hormones bind to their receptors and no more hormone is released from their cell of origin, the concentration of hormone bound to carrier proteins will (increase / decrease).
14. The strength with which a ligand (chemical messenger) will bind with a receptor is referred to as its               .

15. Name a non-steroidal antiinflammatory drug.