Which bond is broken by the enzyme Helicase?

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

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

Remark: Helicase separates the two DNA strands by breaking the hydrogen bonds holding the nitrogenous bases together.

The leading strand is synthesized in which direction?

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

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

Remark: The leading strand is synthesized continuously in the 5-prime to 3-prime direction, moving towards the replication fork.

Which mutation results in the change of a single base pair?

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

• Point mutation
• Frameshift mutation
• Deletion
• Duplication
Correct Option: A  [ Point mutation ]

Remark: A point mutation involves the substitution of a single base pair, as seen in Sickle Cell Anemia.

Frameshift mutations are caused by?

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

• Insertion or Deletion of bases
• Substitution of bases
• Methylation of bases
• Replication errors
Correct Option: A  [ Insertion or Deletion of bases ]

Remark: Insertions or deletions of nucleotides (not in multiples of 3) shift the reading frame of the genetic code.

The initiator tRNA in prokaryotes carries which amino acid?

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

• Formyl-methionine
• Methionine
• Valine
• Lysine
Correct Option: A  [ Formyl-methionine ]

Remark: In prokaryotes, the initiator tRNA is charged with N-formylmethionine (fMet). In eukaryotes, it is Methionine.

Which site on the ribosome accepts the new incoming aminoacyl-tRNA?

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

• A-site
• P-site
• E-site
• M-site
Correct Option: A  [ A-site ]

Remark: The A-site (Aminoacyl site) is where the new tRNA carrying an amino acid enters the ribosome.

During translation, the polypeptide chain is held at which site?

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

• P-site
• A-site
• E-site
• O-site
Correct Option: A  [ P-site ]

Remark: The P-site (Peptidyl site) holds the tRNA carrying the growing polypeptide chain.

Termination of translation occurs when the ribosome encounters?

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

• A Stop Codon
• A Start Codon
• A Promoter
• An Intron
Correct Option: A  [ A Stop Codon ]

Remark: When a stop codon (UAA, UAG, UGA) reaches the A-site, no tRNA binds; instead, Release Factors bind to terminate translation.

Which scientist proved that DNA replication is semi-conservative using Nitrogen isotopes?

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

• Meselson and Stahl
• Hershey and Chase
• Taylor
• Griffith
Correct Option: A  [ Meselson and Stahl ]

Remark: Meselson and Stahl used N-15 and N-14 isotopes to prove the semi-conservative mode of replication.

What is the function of the enzyme Permease in the Lac Operon?

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

• Transport lactose into the cell
• Hydrolyze lactose
• Transfer acetyl group
• Bind repressor
Correct Option: A  [ Transport lactose into the cell ]

Remark: Permease facilitates the entry of lactose into the bacterial cell.