Molecular Basis of Inheritance MCQs

In eukaryotes, RNA Polymerase I transcribes large rRNAs (28S, 18S, 5.8S). RNA Polymerase II transcribes hnRNA (heterogeneous nuclear RNA), which processes into mRNA. RNA Polymerase III transcribes tRNA, 5S rRNA, and snRNAs. A mnemonic is RMT (I->rRNA, II->mRNA, III->tRNA).

Capping involves adding a 7-methylguanosine cap to the 5-prime end of hnRNA. Tailing involves adding a Poly-A tail (Adenylate residues) to the 3-prime end. Splicing is the removal of non-coding Introns. Exons are the coding sequences that are joined together to form the mature mRNA.

Degenerate means that some amino acids are coded by more than one codon (redundancy). Unambiguous means a specific codon always codes for the same specific amino acid. Universal means the code applies to nearly all organisms. Comma-less means the code is read continuously without pauses or punctuation.

The Anticodon loop contains bases complementary to the mRNA codon. The 3-prime Acceptor Arm binds to the specific amino acid. The 2D secondary structure resembles a Clover-leaf. The actual 3D tertiary structure resembles an Inverted L.

Aminoacyl-tRNA Synthetase activates amino acids and links them to tRNA (charging). The 23S rRNA in bacteria acts as a Ribozyme (Peptidyl transferase) to form peptide bonds. Release Factors bind to stop codons to terminate the process. UTRs are regions before the start and after the stop codon that improve the efficiency of translation.

The i gene codes for the Repressor protein. The z gene codes for Beta-galactosidase (breaks down lactose). The y gene codes for Permease (transports lactose into cell). The a gene codes for Transacetylase.

Lactose acts as the Inducer by binding to the Repressor and inactivating it. The Repressor protein normally binds to the Operator region to physically block transcription. The Operator is the specific DNA sequence where the Repressor binds. The Promoter is the sequence where RNA Polymerase binds to initiate transcription.

Expressed Sequence Tags (ESTs) involve sequencing only the genes that are expressed as RNA. Sequence Annotation involves sequencing the whole genome (coding and non-coding) and assigning functions later. BAC (Bacterial Artificial Chromosome) and YAC (Yeast Artificial Chromosome) are vectors used to clone large DNA fragments. The Sanger Method is the principle behind automated DNA sequencing.

The human haploid genome contains approximately 3.3 billion base pairs (specifically 3.1647 billion). Less than 2% of the genome codes for proteins. The largest known human gene is Dystrophin, spanning 2.4 million bases. Chromosome 1 has the highest number of genes (2968).

Digestion refers to cutting DNA into fragments using restriction enzymes. Gel Electrophoresis separates these fragments based on size (smaller fragments move faster). Southern Blotting is the transfer of these separated fragments onto a synthetic membrane like nitrocellulose. Hybridization involves binding radioactive VNTR probes to specific complementary DNA sequences on the membrane.