Physiology Q5

Question 1

Which of the following is a characteristic of G protein–coupled receptors (GPCRs)?
* A. They work directly as enzymes.
* B. They consist of a single polypeptide chain that crosses the lipid bilayer seven times.
* C. They open ion channels directly.
* D. They phosphorylate proteins without intermediary complexes.

Answer 1

B. They consist of a single polypeptide chain that crosses the lipid bilayer seven times.

Question 2

What happens to the alpha subunit of the G-protein when a ligand binds to a GPCR?
* A. It binds GDP and becomes inactive.
* B. It remains in an inactive state bound to GTP.
* C. It binds GTP and becomes active.
* D. It dissociates from the G-protein and binds directly to the ligand.

Answer 2

C. It binds GTP and becomes active.

Question 3

Which second messenger is synthesized from ATP by adenylyl cyclase when GPCRs are activated?
* A. cGMP
* B. cAMP
* C. PIP2
* D. IP3

Answer 3

B. cAMP

Question 4

Cholera can be caused by the ADP ribosylation of which subunit of the G-protein?
* A. β-subunit
* B. γ-subunit
* C. α-subunit
* D. All subunits

Answer 4

C. α-subunit

Question 5

Which enzyme is activated by cAMP to exert its effects inside the cell?
* A. Protein kinase C
* B. Adenylyl cyclase
* C. Phospholipase C
* D. Protein kinase A (PKA)

Answer 5

D. Protein kinase A (PKA)

Question 6

What is the function of phospholipase C-β (PLCβ) in GPCR signaling?
* A. It activates adenylyl cyclase.
* B. It cleaves PIP2 into IP3 and diacylglycerol.
* C. It binds to GTP and activates downstream signaling.
* D. It dephosphorylates cAMP.

Answer 6

B. It cleaves PIP2 into IP3 and diacylglycerol.

Question 7

Which of the following is true about receptor tyrosine kinases (RTKs)?
* A. They use G-proteins to relay the signal.
* B. Ligand binding causes receptor chains to dimerize and undergo trans
autophosphorylation.
* C. They phosphorylate serine residues in downstream proteins.
* D. They degrade cAMP after signal transduction.

Answer 7

B. Ligand binding causes receptor chains to dimerize and undergo trans
autophosphorylation.

Question 8

Which signaling module is activated by Ras in receptor tyrosine kinase pathways?
* A. PLCβ
* B. MAP kinase module (Raf, Mek, Erk)
* C. Phosphodiesterase
* D. JAK/STAT pathway

Answer 8

B. MAP kinase module (Raf, Mek, Erk)

Question 9

The JAK/STAT signaling pathway is associated with which type of receptors?
* A. Ion-channel coupled receptors
* B. G-protein coupled receptors
* C. Tyrosine kinase-associated receptors
* D. Serine-Threonine kinase receptors

Answer 9

C. Tyrosine kinase-associated receptors

Question 10

Which receptor type is known for phosphorylating proteins on serine or threonine residues
instead of tyrosine residues?
* A. Receptor tyrosine kinases
* B. G-protein coupled receptors
* C. Serine-Threonine kinase receptors
* D. Receptor tyrosine phosphatases

Answer 10

C. Serine-Threonine kinase receptors

Question 11

What is the primary role of diacylglycerol (DAG) in GPCR signaling?
* A. It activates protein kinase A (PKA).
* B. It binds and opens calcium channels.
* C. It assists in prostaglandin synthesis and activates protein kinase C (PKC).
* D. It deactivates adenylyl cyclase.

Answer 11

C. It assists in prostaglandin synthesis and activates protein kinase C (PKC).

Question 12

Which of the following is responsible for raising calcium concentration in the cytosol
during GPCR signaling?
* A. Diacylglycerol (DAG)
* B. IP3-gated Ca2+ channels in the endoplasmic reticulum
* C. cAMP activation of Ca2+ pumps
* D. GTP hydrolysis by the alpha subunit of the G-protein

Answer 12

B. IP3-gated Ca2+ channels in the endoplasmic reticulum

Question 13

What type of receptor directly synthesizes cGMP after ligand binding?
* A. GPCRs
* B. Receptor tyrosine kinases (RTKs)
* C. Guanylyl cyclase receptors
* D. Tyrosine phosphatases

Answer 13

C. Guanylyl cyclase receptors

Question 14

The Ras protein belongs to which family of proteins?
* A. Serine-threonine kinases
* B. Tyrosine phosphatases
* C. GTPases
* D. Adenylyl cyclases

Answer 14

C. GTPases

Question 15

In the Ras-Raf-MAPK signaling pathway, what happens when Ras is bound to GTP?
* A. Ras remains inactive.
* B. Ras becomes active and initiates a signaling cascade.
* C. Ras dissociates from the receptor and inhibits downstream signaling.
* D. Ras binds to ATP and triggers phosphorylation.

Answer 15

B. Ras becomes active and initiates a signaling cascade.

Question 16

What is the result of “trans autophosphorylation” in receptor tyrosine kinases (RTKs)?
* A. The receptor activates the G-protein.
* B. The receptor chains phosphorylate each other on tyrosine residues.
* C. cAMP is produced by adenylyl cyclase.
* D. The ligand dissociates from the receptor.

Answer 16

B. The receptor chains phosphorylate each other on tyrosine residues.

Question 17

Which domain is essential for proteins to bind to the phosphorylated sites on receptor
tyrosine kinases (RTKs)?
* A. SH2/SH3 domain
* B. GTP-binding domain
* C. ATP-binding domain
* D. IP3-binding domain

Answer 17

A. SH2/SH3 domain

Question 18

Which of the following describes the JAK/STAT pathway?
* A. Ligand binding to the receptor activates Ras, which then activates MAPK.
* B. JAK phosphorylates the receptor and STAT proteins, which translocate to the nucleus.
* C. Adenylyl cyclase is activated, producing cAMP, which activates PKA.
* D. Phospholipase C is activated, generating DAG and IP3.

Answer 18

B. JAK phosphorylates the receptor and STAT proteins, which translocate to the nucleus.

Question 19

Receptor tyrosine phosphatases are characterized by which type of activity?
* A. They phosphorylate tyrosine residues on downstream proteins.
* B. They remove phosphate groups from tyrosine residues.
* C. They synthesize cGMP from GTP.
* D. They activate adenylyl cyclase.

Answer 19

B. They remove phosphate groups from tyrosine residues.

Question 20

Which receptor type is associated with SMAD signaling?
* A. G-protein coupled receptors
* B. Receptor tyrosine kinases (RTKs)
* C. Serine-Threonine kinase receptors
* D. Receptor tyrosine phosphatases

Answer 20

C. Serine-Threonine kinase receptors

Question 21

What happens when a ligand binds to a G-protein coupled receptor (GPCR)?
o A) The receptor directly opens an ion channel.
o B) The receptor activates a G-protein, which then activates or inactivates a
separate enzyme or channel.
o C) The receptor itself acts as an enzyme.
o D) The receptor undergoes trans autophosphorylation.

Answer 21

B) The receptor activates a G-protein, which then activates or inactivates a
separate enzyme or channel.

Question 22

Which of the following is NOT a major class of cell surface receptors?
o A) Ion-channel coupled receptors
o B) G-protein coupled receptors
o C) Enzyme-coupled receptors
o D) Nuclear receptors

Answer 22

D) Nuclear receptors

Question 23

What happens when a ligand binds to an enzyme-coupled receptor?
o A) The receptor directly opens an ion channel.
o B) The receptor activates a G-protein.
o C) The receptor itself acts as an enzyme or associates with an enzyme.
o D) The receptor undergoes trans autophosphorylation.

Answer 23

C) The receptor itself acts as an enzyme or associates with an enzyme.

Question 24

Which of the following is a secondary messenger involved in signal
transduction?
o A) ATP
o B) GTP
o C) cAMP
o D) GDP

Answer 24

C) cAMP

Question 25

What is the function of phosphodiesterases in cell signaling? o A) To synthesize cAMP from ATP. o B) To hydrolyze cGMP into GMP. o C) To activate protein kinase A (PKA). o D) To bind and open IP3 gated Ca2+ channels.

Answer 25

B) To hydrolyze cGMP into GMP.

Question 26

What is the role of protein kinases in intracellular signaling? o A) To remove phosphate groups from signaling proteins. o B) To add phosphate groups to signaling proteins. o C) To bind GTP to signaling proteins. o D) To hydrolyze GTP to GDP.

Answer 26

B) To add phosphate groups to signaling proteins.

Question 27

Which type of signaling involves direct cell-to-cell contact? o A) Paracrine signaling o B) Endocrine signaling o C) Autocrine signaling o D) Juxtacrine signaling

Answer 27

D) Juxtacrine signaling

Question 28

Which of the following molecules can diffuse through the plasma membrane and bind to intracellular receptors? o A) Peptide hormones o B) Amide hormones o C) Steroid hormones o D) None of the above

Answer 28

C) Steroid hormones

Question 29

Which of the following is NOT a secondary messenger? o A) cAMP o B) cGMP o C) Ca2+ o D) ATP

Answer 29

D) ATP

Question 30

Which type of signaling involves a cell acting on itself? o A) Paracrine signaling o B) Endocrine signaling o C) Autocrine signaling o D) Juxtacrine signaling

Answer 30

C) Autocrine signaling

Question 31

Which of the following is a characteristic of endocrine signaling? o A) It acts on neighboring cells. o B) It relies on diffusion and act on distant cells. o C) It involves direct cell-to-cell contact. o D) It acts on the same cell that produces the signal.

Answer 31

B) It relies on diffusion and act on distant cells.

Question 32

What type of receptor is the insulin receptor? o A) G-protein coupled receptor o B) Ion-channel coupled receptor o C) Receptor tyrosine kinase o D) Nuclear receptor

Answer 32

C) Receptor tyrosine kinase

Question 33

What is the primary function of nuclear receptors? o A) To bind to cell surface receptors o B) To act as transcription factors and regulate gene expression o C) To open ion channels in the plasma membrane o D) To activate G-proteins

Answer 33

B) To act as transcription factors and regulate gene expression

Question 34

What happens when a ligand binds to a nuclear receptor? o A) The receptor undergoes trans autophosphorylation. o B) The receptor activates a G-protein. o C) The receptor-ligand complex binds to DNA and regulates gene expression. o D) The receptor opens an ion channel.

Answer 34

C) The receptor-ligand complex binds to DNA and regulates gene expression.

Question 35

Which of the following is NOT a type of nuclear receptor? o A) Estrogen receptor o B) Androgen receptor o C) Insulin receptor o D) Thyroid hormone receptor

Answer 35

C) Insulin receptor

Question 36

What is the primary function of nitric oxide (NO) in the cardiovascular system? o A) To increase blood pressure o B) To mediate smooth muscle relaxation and vasodilation o C) To inhibit platelet aggregation o D) To activate G-proteins

Answer 36

B) To mediate smooth muscle relaxation and vasodilation

Question 37

Which enzyme is activated by NO to increase cGMP levels? o A) Soluble guanylyl cyclase (sGC) o B) Adenylyl cyclase o C) Protein kinase G (PKG) o D) Phosphodiesterase

Answer 37

A) Soluble guanylyl cyclase (sGC)

Question 38

Which of the following is a downstream effect of cGMP activation? o A) Increased gluconeogenesis o B) Smooth muscle contraction o C) Smooth muscle relaxation o D) Increased blood pressure

Answer 38

C) Smooth muscle relaxation

Question 39

What is the effect of NO on renal blood flow? o A) It decreases renal blood flow. o B) It has no effect on renal blood flow. o C) It increases renal blood flow. o D) It inhibits renal blood flow.

Answer 39

C) It increases renal blood flow.

Question 40

Once produced, nitric oxide (NO) can diffuse to neighboring cells * True * False

Answer 40

True

Question 41

You know that GTP-binding proteins are frequently used in signal transduction as On/off switches. Given that what you know about the mechanism of Vibrio Cholera toxin, what is likely happening in patients suffering with cholera? * G protein is GDP bound * Alpha subunit can no longer hydrolyze bound GTP * Adenylyl cyclase is in an unstimulated state * Prolonged cessation in cAMP concentration within intestinal cells

Answer 41

Alpha subunit can no longer hydrolyze bound GTP