The enzyme that adds nucleotides to the growing DNA strand during replication is:
A. Ligase
B. DNA polymerase
C. Primase
D. Helicase
Answer: Option B
Solution (By JKSSB Mock Tests)
DNA polymerase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, extending the new strand complementary to the template. Helicase unwinds DNA, ligase joins fragments, primase synthesizes RNA primer. In prokaryotes, DNA polymerase III is the main replicative enzyme.
Consider statements about angiosperms: 1. They have enclosed seeds. 2. They exhibit double fertilization. 3. All angiosperms are trees. Which are correct?
Explanation:
Angiosperms are flowering plants where seeds are enclosed within a mature ovary (fruit). They are characterized by double fertilization, where one male gamete fuses with the egg and the other with the secondary nucleus. They exhibit immense diversity in habit, ranging from tiny aquatic Wolffia to massive trees, so not all are trees. Statements 1 and 2 are correct.
Explanation:
Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during the pachytene stage of prophase I. The synaptonemal complex facilitates this. Chiasmata become visible in diplotene when the synaptonemal complex dissolves. Leptotene is chromosome condensation, zygotene is synapsis. This process is crucial for genetic variation.
Explanation:
Prokaryotic cells lack a true nucleus; their genetic material is located in a nucleoid region. They possess 70S ribosomes (50S+30S subunits), whereas eukaryotic cells have 80S ribosomes. Prokaryotes generally have a cell wall (except Mycoplasma) and circular DNA, not linear. Membrane-bound organelles like mitochondria, ER are absent. Examples: bacteria and blue-green algae. This distinction is fundamental in cell biology.
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