VNTR stands for Variable Number of Tandem Repeats, a class of satellite DNA used as a marker. Polymorphism is a variation in DNA sequence observed in a population at a frequency greater than 0.01 (1%). A Probe is a radioactive single-stranded DNA used to detect specific sequences. PCR (Polymerase Chain Reaction) is used to amplify small DNA samples to increase sensitivity.
Question 542 of 668
📘 CLASS XII
Match List-I with List-II.
List-I (Chromatin Structure)
List-II (Property)
A. Heterochromatin
I. Transcriptionally Active
B. Euchromatin
II. Beads-on-string structure
C. Nucleosome
III. Densely packed, Dark stain
D. Histones
IV. Positively charged proteins
Heterochromatin is the densely packed, dark-staining region of chromatin that is transcriptionally inactive. Euchromatin is the loosely packed, light-staining region that is transcriptionally active. The Nucleosome consists of DNA wrapped around a histone octamer, giving the appearance of "beads-on-string". Histones are the positively charged basic proteins that form the core of the nucleosome.
Question 543 of 668
📘 CLASS XII
Which isotope was used by Meselson and Stahl to distinguish between heavy and light DNA?
Meselson and Stahl used the heavy isotope of nitrogen (N-15) and the normal light isotope (N-14) to prove the semi-conservative nature of DNA replication. N-15 is not a radioisotope but a heavy isotope distinguishable by centrifugation.
Question 544 of 668
📘 CLASS XII
Taylor and colleagues used which radioactive molecule to prove semi-conservative replication in Vicia faba?
Taylor and his colleagues used radioactive thymidine to detect the distribution of newly synthesized DNA in the chromosomes of Vicia faba (faba beans), proving semi-conservative replication in eukaryotes.
Question 545 of 668
📘 CLASS XII
The enzyme responsible for relieving torsional strain (supercoiling) ahead of the replication fork is?
As Helicase unwinds the DNA, tension or supercoiling builds up ahead of the fork. Topoisomerase (specifically DNA Gyrase in prokaryotes) relieves this tension by cutting and resealing the DNA.
Question 546 of 668
📘 CLASS XII
In DNA replication, the primer used to initiate synthesis is chemically?
DNA polymerase cannot initiate synthesis on its own; it requires a free 3-prime OH group. This is provided by a short stretch of RNA called an RNA primer, synthesized by the enzyme Primase.
Question 547 of 668
📘 CLASS XII
Which enzyme removes the RNA primers after DNA replication in bacteria?
DNA Polymerase I is responsible for removing the RNA primers and filling the gaps with DNA nucleotides. DNA Polymerase III is the main replicating enzyme.
Question 548 of 668
📘 CLASS XII
The discontinuously synthesized DNA fragments on the lagging strand are known as?
The lagging strand is synthesized in short segments called Okazaki fragments because DNA polymerase can only synthesize in the 5-prime to 3-prime direction, moving away from the replication fork on this strand.
Question 549 of 668
📘 CLASS XII
Which enzyme acts as the "molecular glue" to join DNA fragments?
DNA Ligase joins the discontinuous Okazaki fragments on the lagging strand by forming phosphodiester bonds, acting as a molecular glue.
Question 550 of 668
📘 CLASS XII
The energy required for adding nucleotides during DNA replication is provided by?
The substrates for replication are dNTPs (like dATP, dGTP, etc.). They serve a dual purpose: acting as substrates and providing energy through the breakdown of their two terminal phosphates.
