51. The following are true about DNA synthesis:
a. It requires DNA polymerase
b. Reverse transcriptase enzymes are involved
c. Moves in a 3′ → 5′ direction
d. The rate of error in DNA synthesis is 1 in 10⁵ base pairs
Correct answer: a. It requires DNA polymerase
DNA synthesis is catalyzed by DNA polymerase; it proceeds in the 5′ → 3′ direction, reverse transcriptase is not normally involved, and error rate is much lower than 1 in 10⁵.
52. With regard to DNA molecules:
a. They contain adenine, cytosine, guanine, and uracil
b. They can be detected with Western blotting
c. They can be detected with Southern blotting
d. None of these
Correct answer: c. They can be detected with Southern blotting
DNA contains thymine instead of uracil; Western blot detects proteins, whereas Southern blot detects DNA.
53. G-proteins:
a. Are activated by the binding of an extracellular ligand to a membrane receptor
b. Mediate the action of glucocorticoid hormone
c. They are inactivated by cholera toxins
d. None of these
Correct answer: a. Are activated by the binding of an extracellular ligand to a membrane receptor
Hormone-receptor interaction activates G-proteins; glucocorticoids act via intracellular receptors; cholera toxin activates, not inactivates, G-proteins.
54. The following is true about gluconeogenesis:
a. It occurs in liver
b. It occurs in kidney
c. It occurs in adipose tissue
d. Both (a) and (b)
Correct answer: d. Both (a) and (b)
Gluconeogenesis primarily occurs in the liver and to a lesser extent in the renal cortex.
55. With regard to membrane receptors for hormones:
a. They are often glycoproteins
b. They are important for hormones made up of steroid
c. Those for insulin exhibit intrinsic protein kinase activity
d. Both (a) and (c)
Correct answer: d. Both (a) and (c)
Membrane receptors are commonly glycoproteins; insulin receptors contain intrinsic tyrosine kinase activity; steroid hormones use intracellular receptors.
56. The following factors increase the rate of GFR:
a. Decreased albumin concentration in plasma
b. Vasodilation of the afferent arteriole
c. Vasoconstriction of the efferent arteriole
d. All are correct
Correct answer: d. All are correct
All three mechanisms increase glomerular filtration pressure and GFR.
57. Aldosterone secretion is not controlled by:
a. Plasma sodium concentration
b. Plasma calcium concentration
c. Plasma potassium concentration
d. Angiotensin II
Correct answer: b. Plasma calcium concentration
Calcium has no regulatory role; sodium, potassium, and angiotensin II regulate aldosterone release.
58. In pregnancy:
a. Lysozyme in tear film is increased
b. Intraocular pressure is lower
c. Accommodation is decreased
d. All above
Correct answer: d. All above
Pregnancy alters ocular physiology, increasing lysozyme, reducing IOP, and reducing accommodative ability.
59. The following may cause elevated blood urea:
a. Renal disease
b. Steroid therapy
c. Dehydration
d. All above
Correct answer: d. All above
Renal impairment, protein catabolism from steroids, and dehydration all elevate urea levels.
60. The following occur in response to major surgery:
a. Increased potassium loss
b. Increased protein breakdown
c. Sodium and water retention
d. All above
Correct answer: d. All above
Stress response to surgery induces catabolism, electrolyte changes, and fluid retention.
61. Hyperventilation causes:
a. An alkaline urine
b. A fall in plasma bicarbonate concentration
c. Increased cardiac output
d. All above
Correct answer: d. All above
Respiratory alkalosis increases urinary alkalinity, reduces bicarbonate, and increases cardiac output.
62. Bradycardia can occur in response to:
a. Elevated intraocular pressure
b. Ocular massage
c. Pulling of extraocular muscle
d. All above
Correct answer: d. All above
The oculocardiac reflex triggers vagal stimulation and bradycardia.
63. The prothrombin time:
a. Assesses the extrinsic pathway
b. Is prolonged in patients with fat malabsorption
c. Is increased by warfarin
d. All above
Correct answer: d. All above
PT measures the extrinsic pathway; vitamin K deficiency from fat malabsorption prolongs PT; warfarin also increases PT.
64. In human beings, hemorrhage causes:
a. Venous constriction
b. Decreased blood flow to skin
c. A fall in cardiac output
d. All above
Correct answer: d. All above
Compensatory mechanisms aim to preserve core perfusion while cardiac output drops due to volume loss.
65. The respiratory system exchanges gases between the ______ and the _______.
a. Blood vessels, tissue fluids
b. Air in lungs, blood
c. Air in lungs, air in organs
d. Tissue fluid, blood
Correct answer: b. Air in lungs, blood
Gas exchange occurs at the alveolar–capillary membrane.
66. In the lungs, _____ gas enters the blood and _____ gas exits the blood.
a. O₂, PO₄
b. CO₂, H₂O₄
c. CO₂, O₂
d. O₂, CO₂
Correct answer: d. O₂, CO₂
Oxygen diffuses into blood; carbon dioxide diffuses out of blood.
67. Gout:
a. Is characterized by hyperuricemia
b. Causes scleritis
c. Patients should avoid eating offal
d. All above
Correct answer: d. All above
Elevated uric acid defines gout; ocular inflammation can occur; purine-rich offal worsens the condition.
68. The following are true about cell-mediated immunity:
a. Antigen-specific function is the role of T-lymphocytes
b. Cell-mediated immunity can activate complement
c. It is responsible for delayed hypersensitivity reactions
d. Gamma interferon is an important mediator of B-cell activation
Correct answer: a. Antigen-specific function is the role of T-lymphocytes
T-cells mediate cell-mediated immunity and delayed hypersensitivity; complement activation is mainly antibody-mediated; gamma interferon primarily activates macrophages.
69. The following are useful in the diagnosis of HIV infection:
a. Polymerase chain reaction
b. Antibodies by ELISA
c. p24 protein assay
d. All above
Correct answer: d. All above
PCR detects viral RNA; ELISA detects antibodies; p24 antigen is an early infection marker.
70. The following are true about chemicals in allergic reactions:
a. Thromboxane – leukocyte activation
b. Prostaglandin D₂ – vasodilatation
c. Platelet-activating factor – leukocyte activation
d. Heparin – augments inactivation of prostaglandins
Correct answer: c. Platelet-activating factor – leukocyte activation
PAF strongly activates leukocytes; thromboxane causes vasoconstriction; prostaglandin D₂ causes vasodilation; heparin does not inactivate prostaglandins.
71. In AIDS, the following abnormalities are seen:
a. Persistent lymphopenia
b. Decreased interleukin-2 production
c. Impaired delayed cutaneous hypersensitivity
d. All above
Correct answer: d. All above
AIDS causes severe T-cell depletion, cytokine defects, and loss of cell-mediated immunity.
72. Purines:
a. Include guanine
b. Are metabolized to uric acid
c. Are mainly synthesized in the liver
d. All above
Correct answer: d. All above
Purines include adenine and guanine, are synthesized largely in the liver, and ultimately form uric acid.
73. Vitamin B12:
a. Is essential for folate metabolism
b. Is attached to a glycoprotein in circulation
c. Its deficiency causes hypersegmented neutrophils
d. All above
Correct answer: d. All above
B12 is required for folate activation, transported bound to transcobalamin, and deficiency produces megaloblastic changes.
74. Folic acid:
a. Is water-soluble
b. Is absorbed in the stomach
c. Deficiency leads to aplastic anemia
d. Deficiency occurs with methotrexate treatment
Correct answer: d. Deficiency occurs with methotrexate treatment
Folate is absorbed in the jejunum; deficiency causes megaloblastic anemia, not aplastic anemia; methotrexate inhibits folate metabolism.
75. Prostaglandins:
a. Contain 20 carbon atoms
b. Are unsaturated fatty acids with a cyclopentane ring
c. Classified according to the structure of the cyclopentane ring
d. All above
Correct answer: d. All above
Prostaglandins are 20-carbon eicosanoids with a cyclopentane ring and classification based on ring structure.