Which molecule serves as the structural component of ribosomes?

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

• mRNA
• tRNA
• rRNA
• DNA
Correct Option: C  [ rRNA ]

Remark: Ribosomal RNA (rRNA) combines with proteins to form the structural units of the ribosome (both large and small subunits) and also has catalytic activity.

In the Lac operon, lactose is hydrolyzed into?

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

• Glucose + Glucose
• Glucose + Fructose
• Glucose + Galactose
• Galactose + Galactose
Correct Option: C  [ Glucose + Galactose ]

Remark: The enzyme beta-galactosidase hydrolyzes the disaccharide lactose into two monosaccharides: glucose and galactose.

The probe used in DNA fingerprinting is usually?

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

• Double stranded DNA
• Single stranded radioactive DNA
• Protein
• RNA
Correct Option: B  [ Single stranded radioactive DNA ]

Remark: Probes are single-stranded DNA or RNA molecules tagged with radioactive isotopes that hybridize to complementary sequences (VNTRs) on the membrane.

Polycistronic mRNA is characteristic of?

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

• Prokaryotes
• Eukaryotes
• Viruses
• Humans
Correct Option: A  [ Prokaryotes ]

Remark: Prokaryotic mRNA is often polycistronic, meaning it carries coding information for several proteins (genes) that are translated together (e.g., Lac operon). Eukaryotic mRNA is typically monocistronic.

The first amino acid added during translation in prokaryotes is?

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

• Methionine
• Formyl-methionine
• Valine
• Glycine
Correct Option: B  [ Formyl-methionine ]

Remark: In prokaryotes, the initiator tRNA carries a modified methionine called N-formylmethionine (fMet). In eukaryotes, it is unmodified methionine.

Which site of the ribosome holds the tRNA carrying the growing polypeptide chain?

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

• A site
• P site
• E site
• Binding site
Correct Option: B  [ P site ]

Remark: The P (Peptidyl) site holds the tRNA attached to the growing polypeptide chain. The A site holds the incoming amino acid, and the E site is for exit.

Select the correct complementary base pairing rule.

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

• Purine pairs with Purine
• Pyrimidine pairs with Pyrimidine
• Purine pairs with Pyrimidine
• None
Correct Option: C  [ Purine pairs with Pyrimidine ]

Remark: To maintain a uniform distance between the two strands of the double helix, a large purine (A or G) always pairs with a small pyrimidine (T or C).

The net electric charge of DNA is?

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

• Positive
• Negative
• Neutral
• Variable
Correct Option: B  [ Negative ]

Remark: DNA is negatively charged at physiological pH due to the phosphate groups in the backbone, which release protons.

Which of the following is required for the initiation of transcription in E. coli?

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

• Rho factor
• Sigma factor
• AUG codon
• Primer
Correct Option: B  [ Sigma factor ]

Remark: The Sigma factor is essential for the RNA polymerase holoenzyme to recognize and bind to the promoter region to initiate transcription.

A terminator sequence is involved in?

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

• Starting replication
• Stopping replication
• Starting transcription
• Stopping transcription
Correct Option: D  [ Stopping transcription ]

Remark: The terminator is a DNA sequence that signals the RNA polymerase to stop transcription and release the RNA transcript.