Which of the following is considered the central dogma of molecular biology?

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

• Protein -> RNA -> DNA
• DNA -> Protein -> RNA
• DNA -> RNA -> Protein
• RNA -> DNA -> Protein
Correct Option: C  [ DNA -> RNA -> Protein ]

Remark: The central dogma of molecular biology describes the flow of genetic information within a biological system. It states that DNA replicates itself, DNA is transcribed into RNA, and RNA is then translated into proteins. This flow is unidirectional in most organisms, although exceptions like reverse transcription exist in retroviruses.

Which component is NOT found in a nucleoside?

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

• Phosphate group
• Nitrogenous base
• Pentose sugar
• Heterocyclic ring
Correct Option: A  [ Phosphate group ]

Remark: A nucleoside consists only of a nitrogenous base attached to a pentose sugar via an N-glycosidic bond. When a phosphate group is added to the 5-prime carbon of the sugar in a nucleoside, it becomes a nucleotide. Therefore, the phosphate group is the distinguishing component between a nucleoside and a nucleotide.

The bond formed between the pentose sugar and the nitrogenous base in a nucleotide is known as?

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

• Phosphodiester bond
• N-glycosidic bond
• Hydrogen bond
• Peptide bond
Correct Option: B  [ N-glycosidic bond ]

Remark: The nitrogenous base is linked to the pentose sugar through an N-glycosidic bond. This bond connects the first carbon of the sugar to a nitrogen atom of the base (N1 in pyrimidines or N9 in purines). This linkage forms a nucleoside.

Which of the following nitrogenous bases is a purine?

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

• Cytosine
• Thymine
• Uracil
• Adenine
Correct Option: D  [ Adenine ]

Remark: Nitrogenous bases are categorized into purines and pyrimidines. Purines, such as Adenine and Guanine, are characterized by a double-ring structure consisting of a nine-membered ring. Pyrimidines, like Cytosine, Thymine, and Uracil, have a single six-membered ring structure.

In DNA, Adenine pairs with Thymine through how many hydrogen bonds?

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

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

Remark: According to the base-pairing rules derived from the double helix model, Adenine pairs specifically with Thymine in DNA. These two bases are held together by two hydrogen bonds. In contrast, Cytosine pairs with Guanine via three hydrogen bonds.

What is the length of one complete turn (pitch) of the DNA helix?

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

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

Remark: The B-form DNA helix makes a complete 360-degree turn every 3.4 nanometers (or 34 Angstroms). Since there are roughly 10 base pairs per turn, the distance between adjacent base pairs is approximately 0.34 nanometers.

Which histone protein acts as a linker, connecting two nucleosomes?

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

• H2A
• H2B
• H3
• H1
Correct Option: D  [ H1 ]

Remark: The nucleosome core particle consists of an octamer of histones (two each of H2A, H2B, H3, and H4). The H1 histone is not part of this core octamer; instead, it binds to the DNA as it enters and exits the nucleosome, acting as a linker or plug that stabilizes the chromatin structure.

Histones are rich in which basic amino acids?

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

• Valine and Leucine
• Lysine and Arginine
• Aspartic acid and Glutamic acid
• Phenylalanine and Tyrosine
Correct Option: B  [ Lysine and Arginine ]

Remark: Histones are positively charged, basic proteins because they are rich in basic amino acid residues, specifically Lysine and Arginine. These positive charges allow histones to bind tightly to the negatively charged phosphate backbone of DNA.

The transcriptionally active and loosely packed region of chromatin is called?

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

• Heterochromatin
• Nucleosome
• Euchromatin
• Chromatid
Correct Option: C  [ Euchromatin ]

Remark: Chromatin exists in two forms. Euchromatin is loosely packed, stains lightly, and is transcriptionally active, meaning it allows for RNA synthesis. Heterochromatin is densely packed, stains darkly, and is generally transcriptionally inactive.

Which scientist(s) provided the unequivocal proof that DNA is the genetic material?

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

• Griffith
• Avery, MacLeod, and McCarty
• Hershey and Chase
• Watson and Crick
Correct Option: C  [ Hershey and Chase ]

Remark: While Griffith and Avery et al. provided early evidence, the unequivocal proof that DNA is the genetic material came from Alfred Hershey and Martha Chase in 1952. They used radioactive phosphorus to label DNA and radioactive sulfur to label proteins in bacteriophages, showing that only DNA entered the bacterial cell to direct viral reproduction.