PHAR 502 THYROID | QUESTIONS AND ANSWERS | WITH COMPLETE SOLUTION/NEWEST
UPDATE!!!
Question 1
What is the primary functional unit of the thyroid gland?
A) Thyroglobulin
B) Thyroid follicle
C) C-cells
D) Islets of Langerhans
E) Colloid cyst
Correct Answer: B) Thyroid follicle
Rationale: The thyroid follicle is the fundamental structural and functional unit of the
thyroid gland, consisting of a layer of follicular cells surrounding a central lumen filled
with colloid.
Question 2
Thyroid hormones T3 and T4 are synthesized from which amino acid precursor?
A) L-Tryptophan
B) L-Phenylalanine
C) L-Tyrosine
D) L-Histidine
E) L-Proline
Correct Answer: C) L-Tyrosine
Rationale: The synthesis of thyroid hormones begins with the iodination of tyrosine residues
on the protein thyroglobulin.
Question 3
In the chemical structure of thyroid hormones, what is the approximate bond angle between the
phenyl and tyrosyl groups?
A) 45 degrees
B) 120 degrees
C) 180 degrees
D) 90 degrees
E) 109.5 degrees
Correct Answer: D) 90 degrees
Rationale: The phenyl and tyrosyl rings are oriented perpendicular to one another, resulting
in a 90-degree bond angle.
Question 4
What is the pKa value of Triiodothyronine (T3)?
A) 6.73
B) 7.40
C) 8.47
D) 9.12
, Page 2
E) 10.5
Correct Answer: C) 8.47
Rationale: T3 has a pKa of 8.47, which influences its ionization state and protein binding
characteristics at physiological pH.
Question 5
What is the pKa value of Thyroxine (T4)?
A) 6.73
B) 8.47
C) 4.55
D) 7.20
E) 8.00
Correct Answer: A) 6.73
Rationale: T4 has a significantly lower pKa (6.73) than T3, making it more acidic and more
ionized at physiological pH.
Question 6
At a physiological pH of 7.4, approximately what percentage of T3 is ionized?
A) 10%
B) 50%
C) 80%
D) 99%
E) 5%
Correct Answer: A) 10%
Rationale: Because its pKa (8.47) is higher than the physiological pH (7.4), only a small
fraction (10%) of T3 exists in the ionized form.
Question 7
At a physiological pH of 7.4, approximately what percentage of T4 is ionized?
A) 10%
B) 25%
C) 50%
D) 80%
E) 95%
Correct Answer: D) 80%
Rationale: T4 has a pKa of 6.73; since this is lower than 7.4, the majority (80%) of the
molecule is ionized at physiological pH.
Question 8
Which of the following explains why T4 transports in the blood more effectively than T3?
A) T4 is smaller than T3
B) T4 is less ionized than T3
, Page 3
C) T4 is more ionized at physiological pH, leading to better protein binding
D) T4 has fewer iodine atoms
E) T4 is more lipophilic
Correct Answer: C) T4 is more ionized at physiological pH, leading to better protein binding
Rationale: Higher ionization of T4 at physiological pH (80%) allows it to bind more readily
to albumin and other transport proteins in the blood compared to T3.
Question 9
Which chemical characteristic of T3 makes its binding at nuclear target sites easiest?
A) Ionic bonding
B) Van der Waals forces
C) Ability to Hydrogen Bond
D) Covalent bonding
E) Lack of iodine
Correct Answer: C) Ability to Hydrogen Bond
Rationale: The specific structure of T3 allows for effective hydrogen bonding, which is the
primary interaction facilitating its binding to receptors at target sites.
Question 10
What is the clinically preferred method for treating most cases of hypothyroidism?
A) T3 dosing alone
B) T4 (Levothyroxine) dosing
C) Iodine supplementation only
D) Desiccated thyroid extract only
E) High protein diet
Correct Answer: B) T4 (Levothyroxine) dosing
Rationale: Levothyroxine (T4) is the drug of choice because it provides a stable reservoir
that the body can peripherally convert to the active T3 as needed.
Question 11
What is the specific function of Thyroid Peroxidase (TPO)?
A) Transport of iodide into the cell
B) Cleavage of TRH
C) Addition of iodide onto tyrosine attached to thyroglobulin
D) Conversion of T4 to reverse T3
E) Binding of TSH to its receptor
Correct Answer: C) Addition of iodide onto tyrosine attached to thyroglobulin
Rationale: TPO is the key enzyme that catalyzes the iodination of tyrosine residues and the
subsequent coupling to form thyroid hormones.
Question 12
What is the most common chemical form of iodine found in the body?
UPDATE!!!
Question 1
What is the primary functional unit of the thyroid gland?
A) Thyroglobulin
B) Thyroid follicle
C) C-cells
D) Islets of Langerhans
E) Colloid cyst
Correct Answer: B) Thyroid follicle
Rationale: The thyroid follicle is the fundamental structural and functional unit of the
thyroid gland, consisting of a layer of follicular cells surrounding a central lumen filled
with colloid.
Question 2
Thyroid hormones T3 and T4 are synthesized from which amino acid precursor?
A) L-Tryptophan
B) L-Phenylalanine
C) L-Tyrosine
D) L-Histidine
E) L-Proline
Correct Answer: C) L-Tyrosine
Rationale: The synthesis of thyroid hormones begins with the iodination of tyrosine residues
on the protein thyroglobulin.
Question 3
In the chemical structure of thyroid hormones, what is the approximate bond angle between the
phenyl and tyrosyl groups?
A) 45 degrees
B) 120 degrees
C) 180 degrees
D) 90 degrees
E) 109.5 degrees
Correct Answer: D) 90 degrees
Rationale: The phenyl and tyrosyl rings are oriented perpendicular to one another, resulting
in a 90-degree bond angle.
Question 4
What is the pKa value of Triiodothyronine (T3)?
A) 6.73
B) 7.40
C) 8.47
D) 9.12
, Page 2
E) 10.5
Correct Answer: C) 8.47
Rationale: T3 has a pKa of 8.47, which influences its ionization state and protein binding
characteristics at physiological pH.
Question 5
What is the pKa value of Thyroxine (T4)?
A) 6.73
B) 8.47
C) 4.55
D) 7.20
E) 8.00
Correct Answer: A) 6.73
Rationale: T4 has a significantly lower pKa (6.73) than T3, making it more acidic and more
ionized at physiological pH.
Question 6
At a physiological pH of 7.4, approximately what percentage of T3 is ionized?
A) 10%
B) 50%
C) 80%
D) 99%
E) 5%
Correct Answer: A) 10%
Rationale: Because its pKa (8.47) is higher than the physiological pH (7.4), only a small
fraction (10%) of T3 exists in the ionized form.
Question 7
At a physiological pH of 7.4, approximately what percentage of T4 is ionized?
A) 10%
B) 25%
C) 50%
D) 80%
E) 95%
Correct Answer: D) 80%
Rationale: T4 has a pKa of 6.73; since this is lower than 7.4, the majority (80%) of the
molecule is ionized at physiological pH.
Question 8
Which of the following explains why T4 transports in the blood more effectively than T3?
A) T4 is smaller than T3
B) T4 is less ionized than T3
, Page 3
C) T4 is more ionized at physiological pH, leading to better protein binding
D) T4 has fewer iodine atoms
E) T4 is more lipophilic
Correct Answer: C) T4 is more ionized at physiological pH, leading to better protein binding
Rationale: Higher ionization of T4 at physiological pH (80%) allows it to bind more readily
to albumin and other transport proteins in the blood compared to T3.
Question 9
Which chemical characteristic of T3 makes its binding at nuclear target sites easiest?
A) Ionic bonding
B) Van der Waals forces
C) Ability to Hydrogen Bond
D) Covalent bonding
E) Lack of iodine
Correct Answer: C) Ability to Hydrogen Bond
Rationale: The specific structure of T3 allows for effective hydrogen bonding, which is the
primary interaction facilitating its binding to receptors at target sites.
Question 10
What is the clinically preferred method for treating most cases of hypothyroidism?
A) T3 dosing alone
B) T4 (Levothyroxine) dosing
C) Iodine supplementation only
D) Desiccated thyroid extract only
E) High protein diet
Correct Answer: B) T4 (Levothyroxine) dosing
Rationale: Levothyroxine (T4) is the drug of choice because it provides a stable reservoir
that the body can peripherally convert to the active T3 as needed.
Question 11
What is the specific function of Thyroid Peroxidase (TPO)?
A) Transport of iodide into the cell
B) Cleavage of TRH
C) Addition of iodide onto tyrosine attached to thyroglobulin
D) Conversion of T4 to reverse T3
E) Binding of TSH to its receptor
Correct Answer: C) Addition of iodide onto tyrosine attached to thyroglobulin
Rationale: TPO is the key enzyme that catalyzes the iodination of tyrosine residues and the
subsequent coupling to form thyroid hormones.
Question 12
What is the most common chemical form of iodine found in the body?
