Which bond connects the phosphate group to the sugar in a nucleotide?

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

• Phosphoester bond
• Hydrogen bond
• Glycosidic bond
• Peptide bond
Correct Option: A  [ Phosphoester bond ]

Remark: A phosphoester bond connects the phosphate group to the 5-prime carbon of the pentose sugar. In a DNA strand, the linkage between two nucleotides involves two such bonds, forming a phosphodiester linkage.

Uracil is present in RNA instead of which base found in DNA?

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

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

Remark: In RNA, Uracil replaces Thymine. Both Uracil and Thymine are pyrimidines that pair with Adenine. Thymine is essentially 5-methyl uracil, making it chemically more stable for DNA storage.

According to Chargaff’s rule, in a double-stranded DNA?

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

• A=C and G=T
• A=G and C=T
• A+G = C+T
• A+T = G+C
Correct Option: C  [ A+G = C+T ]

Remark: Chargaff’s rule states that in double-stranded DNA, the ratio of purines to pyrimidines is 1:1. This means the amount of Adenine plus Guanine (Purines) equals the amount of Cytosine plus Thymine (Pyrimidines). Also, A=T and G=C.

The negatively charged DNA is wrapped around a positively charged histone octamer to form a?

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

• Chromatin fiber
• Nucleosome
• Chromosome
• Solenoid
Correct Option: B  [ Nucleosome ]

Remark: The fundamental unit of chromatin packaging is the nucleosome. It consists of negatively charged DNA wrapped approximately 1.75 times around a positively charged histone octamer core, resembling "beads on a string".

A typical nucleosome contains how many base pairs of DNA helix?

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

• 100 bp
• 200 bp
• 300 bp
• 400 bp
Correct Option: B  [ 200 bp ]

Remark: A typical nucleosome contains approximately 200 base pairs of DNA helix wrapped around the histone octamer. This packaging compacts the DNA significantly.

Which organism has approximately 4.6 x 10^6 base pairs?

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

• Bacteriophage lambda
• E. coli
• Human (haploid)
• Phi X 174
Correct Option: B  [ E. coli ]

Remark: Escherichia coli (E. coli) has a genome size of approximately 4.6 million base pairs (4.6 x 10^6 bp). In comparison, the human haploid genome is much larger at 3.3 x 10^9 bp.

In the Griffith experiment, which strain of Streptococcus pneumoniae was virulent?

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

• R-strain
• S-strain
• Heat-killed S-strain
• Both R and S strains
Correct Option: B  [ S-strain ]

Remark: The S-strain (Smooth) was virulent because it possessed a polysaccharide mucous coat that protected it from the host immune system, causing pneumonia. The R-strain (Rough) lacked this coat and was non-virulent.

Biochemical characterization of the transforming principle showed that transformation was inhibited by?

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

• Protease
• RNase
• DNase
• Lipase
Correct Option: C  [ DNase ]

Remark: Avery, MacLeod, and McCarty showed that adding DNase (an enzyme that degrades DNA) to the heat-killed S-strain extract stopped the transformation of R-strain bacteria. This proved that DNA was the substance causing transformation.

RNA is considered the first genetic material because?

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

• It is more stable than DNA
• It acts as both genetic material and catalyst
• It is double stranded
• It contains Thymine
Correct Option: B  [ It acts as both genetic material and catalyst ]

Remark: The "RNA World" hypothesis suggests RNA was the first genetic material because it can store genetic information (like DNA) and catalyze chemical reactions (like proteins/enzymes, e.g., Ribozymes). DNA evolved later as a more stable storage molecule.

The discontinuously synthesized fragments on the lagging strand are called?

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

• Leading fragments
• Okazaki fragments
• Sigma fragments
• Klenow fragments
Correct Option: B  [ Okazaki fragments ]

Remark: Because DNA polymerase can only synthesize in the 5-to-3 direction and the two DNA strands are antiparallel, one strand (lagging strand) must be synthesized in short, backward bursts. These short segments are called Okazaki fragments.