Molecular Basis of Inheritance MCQs

In prokaryotes, the RNA polymerase core enzyme is capable of elongation but cannot initiate transcription specifically at the promoter. It requires the Sigma factor to recognize the promoter region and initiate the transcription process.

Eukaryotes have three distinct RNA polymerases. RNA Polymerase II is responsible for transcribing the precursor to mRNA, known as heterogeneous nuclear RNA (hnRNA), which undergoes processing to become mature mRNA.

Eukaryotic genes are often split genes, containing coding regions (exons) and non-coding regions (introns). Splicing is the process in which the non-coding introns are removed from the primary RNA transcript, and the exons are joined together to form functional mRNA.

During post-transcriptional processing in eukaryotes, a specialized nucleotide cap made of 7-methylguanosine is added to the 5-prime end of the hnRNA. This cap protects the RNA from degradation and assists in ribosome binding during translation.

Polyadenylation, or tailing, involves adding a sequence of 200-300 adenylate residues to the 3-prime end of the RNA transcript. This Poly-A tail protects the mRNA from enzymatic degradation and aids in its transport out of the nucleus.

The genetic code is degenerate, meaning there are 64 codons for only 20 amino acids. Consequently, some amino acids are coded for by more than one triplet codon (e.g., Serine is coded by 6 different codons).

AUG is the start or initiator codon. It has a dual function: it signals the start of translation and also codes for the amino acid Methionine. The other options (UAA, UAG, UGA) are stop codons.

Har Gobind Khorana synthesized RNA molecules with defined combinations of bases (homopolymers and copolymers) to help decipher the genetic code. Marshall Nirenberg’s cell-free system was also crucial in this discovery.

Transfer RNA (tRNA) acts as an adapter molecule. It has an anticodon loop that reads the genetic code on the mRNA and an acceptor end that binds to a specific amino acid, thus bridging the gap between the nucleotide sequence and the amino acid sequence.

The clover-leaf model represents the secondary structure of tRNA, showing its loops and stems. However, in its actual three-dimensional (tertiary) form, tRNA looks like an inverted "L".