Molecular Biology MCQ on DNA Replication
(Molecular Biology MCQ-07)
(Biology / Life Sciences MCQ: Multiple Choice Questions in Molecular Biology)
(Sample/Model/Practice Questions for CSIR JRF/NET Life Science Examination, ICMR JRF Exam, DBT BET JRF Exam, GATE BT and XL Exam, ICAR JRF NE Exam, PG Entrance Exam, JAM Exam, GS Biology Exam and Medical Entrance Exam)
Different Types of DNA Conformations
(A-DNA, B-DNA and Z-DNA: A Comparison Table)
DNA, the genetic information carrier molecule of the cell, is a long polymer of nucleotides and can adopt different types of structural conformations. The various types of conformations that the DNA can adopt depend on different factors such as:
1. Hydration level
2. Salt concentration
3. DNA sequence
4. Quantity and direction of super-coiling
5. Presence of chemically modified bases
6. Different types of metal ions and its concentrations
7. Presence of polyamines in solution.
The most common types of structural conformations of DNA are named as:
Among these three types, the most abundant type of DNA is B-DNA, commonly known as Watson-Crick Model of DNA double helix. The present post describes the structural features of A, B and Z forms of DNA in a comparative manner. We will also discuss the similarities and differences between A-DNA, B-DNA and Z-DNA.
A-DNA is a rare type of structural conformation that a DNA can adopt under dehydrating conditions. A-DNA is a double stranded helical structure almost similar to B-DNA but with a shorter and more compact structural organization. A-DNA was discovered by Rosalind Franklin and the credit for the naming of A-DNA and B-DNA was also accounted to her. Important structural features of A-DNA are given below:
Ø A-DNA is formed from B-DNA under dehydrating condition.
Ø A-DNA is much wider and flatter than B-DNA.
Ø Similar to B-DNA, the A-DNA is also a right handed helix.
Ø The helix diameter of A-DNA is 26 Å.