Which scientist is credited with the term "Nuclein" after isolating it from pus cells?

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

• Friedrich Miescher
• Altmann
• Watson and Crick
• Gregor Mendel
Correct Option: A  [ Friedrich Miescher ]

Remark: Friedrich Miescher identified a substance inside the nucleus of pus cells from surgical bandages and named it Nuclein. This was the first isolation of what we now know as genetic material.

Who renamed "Nuclein" to "Nucleic Acid" due to its acidic nature?

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

• Friedrich Miescher
• Altmann
• Griffith
• Hershey
Correct Option: B  [ Altmann ]

Remark: While Friedrich Miescher discovered Nuclein, it was Altmann who later observed its acidic properties (due to phosphoric acid) and renamed it Nucleic Acid.

In a DNA double helix, the two strands are coiled in which direction?

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

• Left-handed
• Right-handed
• Zig-zag
• Random
Correct Option: B  [ Right-handed ]

Remark: The standard B-form of DNA described by Watson and Crick is a right-handed helix, meaning it turns clockwise as it moves forward.

Which form of DNA is considered the most common and dominant form in living organisms?

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

• A-DNA
• B-DNA
• Z-DNA
• C-DNA
Correct Option: B  [ B-DNA ]

Remark: B-DNA is the most common form of DNA found in nature and is the structure described by the Watson and Crick double helix model.

The distance between two adjacent base pairs in a B-DNA helix is approximately?

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

• 0.34 nm
• 3.4 nm
• 2.0 nm
• 20 nm
Correct Option: A  [ 0.34 nm ]

Remark: In B-DNA, the rise per base pair is 0.34 nanometers (or 3.4 Angstroms). Since there are 10 base pairs per turn, the total pitch is 3.4 nm.

How many base pairs are present in one complete turn (pitch) of the B-DNA helix?

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

• 5
• 10
• 12
• 20
Correct Option: B  [ 10 ]

Remark: One complete 360-degree turn of the B-DNA helix contains 10 base pairs. This results in a pitch length of 34 Angstroms or 3.4 nm.

The constant distance (diameter) between the two strands of the DNA double helix is?

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

• 34 Angstrom
• 20 Angstrom
• 3.4 Angstrom
• 10 Angstrom
Correct Option: B  [ 20 Angstrom ]

Remark: The diameter of the DNA double helix is approximately 20 Angstroms (2 nm). This uniform width is maintained because a purine (double ring) always pairs with a pyrimidine (single ring).

What ensures the uniform diameter of the DNA double helix?

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

• Purine pairing with Purine
• Pyrimidine pairing with Pyrimidine
• Purine pairing with Pyrimidine
• Sugar-Phosphate backbone
Correct Option: C  [ Purine pairing with Pyrimidine ]

Remark: The pairing of a double-ring purine with a single-ring pyrimidine ensures that the distance between the two strands remains constant at approximately 20 Angstroms throughout the helix.

Which bond provides additional stability to the DNA double helix by interactions between stacked base pairs?

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

• Hydrogen bond
• Stacking interactions
• Phosphodiester bond
• Glycosidic bond
Correct Option: B  [ Stacking interactions ]

Remark: Besides hydrogen bonds between opposite bases, the plane of one base pair stacks over the other, creating stacking interactions (hydrophobic interactions) that confer additional stability to the helical structure.

Which bacteriophage has single-stranded DNA?

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

• Lambda phage
• T4 phage
• Phi X 174
• E. coli
Correct Option: C  [ Phi X 174 ]

Remark: Bacteriophage Phi X 174 is unique because it contains single-stranded DNA comprising 5386 nucleotides, unlike most other organisms which have double-stranded DNA.