Molecular Genetics

3' → 5' and is called the template strand

Step 1: In transcription, RNA polymerase reads the DNA template and synthesizes RNA in the 5'→3' direction. Step 2: To synthesize RNA in 5'→3' direction, it must read the template DNA in the 3'→5' direction (antiparallel rule). Step 3: Therefore, the template strand (also called antisense strand) has polarity 3'→5'. Step 4: The other strand (5'→3') has the same sequence as the RNA produced (except T is replaced by U) and is called the coding strand (sense strand). Step 5: Option A is wrong — the coding strand is 5'→3' but is NOT the template. Option C is wrong — a 5'→3' strand is not the templ

AUG acts only as a start codon and does NOT code for any amino acid

Step 1: AUG is a special codon — it has dual functions. Step 2: AUG acts as the START/initiator codon (beginning of translation). Step 3: Additionally, AUG also codes for the amino acid Methionine (Met). So it does BOTH — it is an initiator AND codes for methionine. Step 4: Therefore, the statement 'AUG does NOT code for any amino acid' is INCORRECT. This makes option B the wrong statement. Step 5: Options A (degeneracy — e.g., GUU, GUC, GUA, GUG all code for valine), C (UAA, UAG, UGA are stop codons), and D (polarity 5'→3') are all correct features of the genetic code.

Introns are removed by splicing, methyl guanosine cap added at 5' end, and poly-A tail added at 3' end

Step 1: Eukaryotic genes have coding sequences (exons) interrupted by non-coding sequences (introns). Step 2: The primary transcript (hnRNA) contains both exons and introns. Step 3: Processing involves three key steps: (a) Splicing — introns are removed and exons are joined together. (b) Capping — an unusual nucleotide, methyl guanosine triphosphate (7-methylguanosine), is added at the 5' end. (c) Tailing — about 200-300 adenylate residues (Poly-A tail) are added at the 3' end. Step 4: This processed mRNA is then transported out of the nucleus for translation. Step 5: Options A and B are wrong

A site (Aminoacyl site)

Step 1: The ribosome has three sites — A (Aminoacyl), P (Peptidyl), and E (Exit). Step 2: During initiation, the initiator tRNA carrying methionine (fMet in prokaryotes) binds to the P site at the AUG start codon — this is a special exception. Step 3: During elongation, each new incoming aminoacyl-tRNA (charged tRNA) enters at the A site, where its anticodon base-pairs with the mRNA codon. Step 4: Peptide bond formation occurs between the amino acid at the A site and the growing peptide chain at the P site (catalysed by peptidyl transferase). Step 5: The uncharged tRNA then moves from P site t