Types of DNA MCQ - Practice Questions with Answers

• Different forms of DNA can be defined as the different structural configuration of DNA, which shows distinct change both in structure and physiology at relative pH and ionic strength of the solution. 
• There are many different forms of DNA like B, A, and Z that are revealed after the X-ray diffraction analysis of DNA crystals at atomic resolution.

B-DNA:

• It is the most common form of DNA, which exists as right-handed double-helical DNA, given by Watson and Crick.
• This structure of DNA is formed under the normal physiology conditions like 92% relative humidity and in low ionic strength.
• The diameter of the B-form helix is 20Å. 
• A single turn in B-form comprises 10 base pairs perpendicular to the helical axis.

A-DNA:

• It is the second most common form of DNA made up of right-handed double-helix.
• It is formed under 75% relative humidity and in the presence of sodium, potassium and caesium ions.
• The diameter of the A-form helix is 23Å.
• A single turn in A-form comprises 11 base pairs perpendicular to the helical axis.
• In A-form, the major groove becomes narrower and more profound, whereas the minor groove becomes wider and flattened.

Z-DNA:

• It exists as left-handed double-helical DNA.
• It is formed under very high salt concentration.
• The coiling of Z-form is in a left-handed and zig-zag pattern.
• The diameter of the Z-form helix is 18Å.
• A single turn in Z-form comprises of 12 base pairs