DNA as an acidic substance present in the nucleus was first identified by _______

[Molecular-Basis-of-Inheritance] [class-xii ]

• Watson and Crick
• Friedrich Miescher
• Wilkins and Franklin
• Chargaff
Correct Option: B  [ Friedrich Miescher ]

Remark: Friedrich Miescher identified DNA in 1869 and named it Nuclein.

Based on X-ray diffraction data, _______ and _______ proposed the Double Helix model.

[Molecular-Basis-of-Inheritance] [class-xii ]

• Meselson and Stahl
• Watson and Crick
• Hershey and Chase
• Griffith and Avery
Correct Option: B  [ Watson and Crick ]

Remark: James Watson and Francis Crick proposed the double helix model in 1953.

Erwin Chargaff observed that for a double-stranded DNA, the ratio between Adenine and Thymine is _______

[Molecular-Basis-of-Inheritance] [class-xii ]

• Variable
• Constant and equals one
• Dependent on species
• Zero
Correct Option: B  [ Constant and equals one ]

Remark: Chargaff's rule states A=T and G=C, so the ratio is one.

The two chains of DNA have _______ polarity.

[Molecular-Basis-of-Inheritance] [class-xii ]

• Parallel
• Antiparallel
• Identical
• Variable
Correct Option: B  [ Antiparallel ]

Remark: One strand runs 5'->3' and the other 3'->5'.

Adenine forms _______ hydrogen bonds with Thymine.

[Molecular-Basis-of-Inheritance] [class-xii ]

• One
• Two
• Three
• Four
Correct Option: B  [ Two ]

Remark: Adenine pairs with Thymine via two hydrogen bonds.

Guanine is bonded with Cytosine with _______ hydrogen bonds.

[Molecular-Basis-of-Inheritance] [class-xii ]

• One
• Two
• Three
• Four
Correct Option: C  [ Three ]

Remark: Guanine and Cytosine are connected by three hydrogen bonds.

The pitch of the DNA helix is _______ nm.

[Molecular-Basis-of-Inheritance] [class-xii ]

• 0.34
• 3.4
• 20
• 34
Correct Option: B  [ 3.4 ]

Remark: The pitch (one complete turn) of the B-DNA helix is 3.4 nm.

There are roughly _______ base pairs in each turn of the helix.

[Molecular-Basis-of-Inheritance] [class-xii ]

• 5
• 10
• 20
• 15
Correct Option: B  [ 10 ]

Remark: One turn of the helix contains approximately 10 base pairs.

The distance between a base pair in a helix is approximately _______ nm.

[Molecular-Basis-of-Inheritance] [class-xii ]

• 3.4
• 0.34
• 2.0
• 20
Correct Option: B  [ 0.34 ]

Remark: The rise per base pair is 0.34 nm.

In DNA, a purine always comes opposite to a _______

[Molecular-Basis-of-Inheritance] [class-xii ]

• Purine
• Pyrimidine
• Sugar
• Phosphate
Correct Option: B  [ Pyrimidine ]

Remark: Purine pairing with pyrimidine ensures a uniform distance between strands.