If a DNA sample has 20% Adenine, what is the percentage of Cytosine?

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

• 20%
• 30%
• 40%
• 80%
Correct Option: B  [ 30% ]

Remark: According to Chargaff’s rule, A=T and G=C. If A=20%, then T=20%. A+T=40%. The remaining 60% must be G+C. Since G=C, Cytosine will be half of 60%, which is 30%.

The core enzyme of RNA polymerase requires which factor for termination?

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

• Sigma
• Rho
• Alpha
• Beta
Correct Option: B  [ Rho ]

Remark: While the Sigma factor is needed for initiation, the Rho factor binds to the RNA polymerase to terminate the transcription process in prokaryotes.

Which of the following is true for the genetic code?

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

• It is ambiguous
• It is overlapping
• It is nearly universal
• It has punctuation
Correct Option: C  [ It is nearly universal ]

Remark: The genetic code is nearly universal, meaning a specific codon codes for the same amino acid in almost all organisms, from bacteria to humans, with very few exceptions (e.g., in mitochondria).

Which scientist proposed the Double Helix model of DNA?

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

• Wilkins and Franklin
• Watson and Crick
• Meselson and Stahl
• Chargaff
Correct Option: B  [ Watson and Crick ]

Remark: James Watson and Francis Crick proposed the famous double helix model of DNA structure in 1953, utilizing X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin.

How many base pairs are present in a typical nucleosome?

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

• 100
• 146
• 200
• 400
Correct Option: C  [ 200 ]

Remark: A nucleosome core particle plus the linker DNA associated with it typically comprises about 200 base pairs of DNA.

In a polyribosome (polysome), multiple ribosomes are attached to?

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

• A single tRNA
• A single mRNA
• A single DNA
• A single rRNA
Correct Option: B  [ A single mRNA ]

Remark: A polysome consists of several ribosomes translating a single mRNA strand simultaneously. This increases the efficiency of protein synthesis, producing multiple copies of the protein from one template.

The DNA dependent DNA polymerase catalyzes polymerization in?

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

• 5-prime to 3-prime direction
• 3-prime to 5-prime direction
• Both directions
• Random direction
Correct Option: A  [ 5-prime to 3-prime direction ]

Remark: All known DNA polymerases synthesize DNA in the 5-prime to 3-prime direction, adding nucleotides to the 3-prime end of the growing strand.

Identify the palindromic sequence used by restriction enzymes.

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

• 5-GAATTC-3 / 3-CTTAAG-5
• 5-GATACC-3 / 3-CCTAGG-5
• 5-CCTTAA-3 / 3-GAATTG-5
• 5-ATCGAT-3 / 3-TAGCTA-5
Correct Option: A  [ 5-GAATTC-3 / 3-CTTAAG-5 ]

Remark: A palindromic sequence reads the same forwards and backwards on complementary strands. 5-GAATTC-3 is the recognition site for EcoRI, and its complement read 5 to 3 is also GAATTC.

The distance between two consecutive base pairs in DNA is?

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

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

Remark: The rise per base pair in B-DNA is 0.34 nanometers. This is derived from the pitch of the helix (3.4 nm) divided by the number of base pairs per turn (10).

Which carbon of the pentose sugar carries the OH group in RNA but not in DNA?

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

• 1-prime
• 2-prime
• 3-prime
• 5-prime
Correct Option: B  [ 2-prime ]

Remark: The sugar in RNA is ribose, which has a hydroxyl (-OH) group at the 2-prime position. In DNA (deoxyribose), this oxygen is missing, leaving just a hydrogen, which contributes to DNA`s stability.