The enzyme that seals nicks in the sugar-phosphate backbone of DNA is:
A. Primase
B. Ligase
C. Helicase
D. DNA polymerase
Answer: Option B
Solution (By JKSSB Mock Tests)
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, sealing breaks in the DNA backbone. It is essential for joining Okazaki fragments on the lagging strand during replication and in DNA repair. Polymerase adds nucleotides, helicase unwinds, primase synthesizes RNA primer.
Consider statements about plant tissues: 1. Xylem transports water upwards. 2. Phloem transports food bidirectionally. 3. Cambium is a permanent tissue. Which are correct?
Explanation:
Xylem is responsible for the unidirectional upward transport of water and minerals from roots to shoots. Phloem transports organic nutrients (food) from sources to sinks, which can be bidirectional (up or down). Cambium (vascular and cork) is a lateral meristematic (dividing) tissue responsible for secondary growth, not a permanent tissue. Thus, statements 1 and 2 are correct.
Consider statements about human nutrition: 1. Calcium is essential for blood clotting. 2. Iron is a component of hemoglobin. 3. Iodine is required for thyroid hormone synthesis. Which are correct?
Explanation:
Calcium ions (Ca2+) are essential cofactors in the blood coagulation cascade, required for converting prothrombin to thrombin. Iron is the central atom in the heme group of hemoglobin, enabling oxygen transport in red blood cells. Iodine is an indispensable component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). All three statements are biologically accurate.
Explanation:
The Haldane effect describes how the oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of CO2. Conversely, deoxygenated blood in the tissues has an increased capacity to carry CO2. This is complementary to the Bohr effect. Exam tip: Bohr = CO2 affects O2; Haldane = O2 affects CO2.
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