Molecular Basis of Inheritance MCQs

DNA Polymerase III is the primary enzyme responsible for the polymerization of nucleotides during DNA replication in E. coli. It adds nucleotides to the growing chain with high speed and accuracy.

DNA polymerases can only add nucleotides to the 3-prime hydroxyl group of a growing strand. Therefore, the direction of synthesis (polymerization) is always 5-prime to 3-prime.

The promoter is a specific DNA sequence located upstream of the structural gene. It provides a binding site for RNA polymerase and defines where transcription of a gene begins.

The coding strand has the same sequence as the mRNA (except T is replaced by U) because the mRNA is complementary to the template strand (which is complementary to the coding strand). So, 5-ATGC-3 becomes 5-AUGC-3 in mRNA.

In prokaryotes, there is no nucleus to separate the genetic material from the cytoplasm. Therefore, ribosomes can attach to the mRNA and begin translation even before transcription is fully complete, coupling the two processes.

Introns are non-coding sequences found within eukaryotic genes. They are transcribed into the primary RNA transcript but are removed (spliced out) before the mRNA is translated into protein.

In eukaryotes, RNA Polymerase III is responsible for transcribing transfer RNA (tRNA), 5S rRNA, and small nuclear RNAs (snRNAs). Mnemonic: RMT (I-rRNA, II-mRNA, III-tRNA).

There are 64 possible codons in the genetic code. However, 3 of them are stop codons (UAA, UAG, UGA) which do not code for any amino acid. Therefore, only 61 codons code for the 20 amino acids.

Sickle cell anemia is caused by a point mutation (substitution) in the beta-globin gene. A single base change (GAG to GUG) results in the substitution of Glutamic acid with Valine, altering the protein structure.

The genetic code is read in triplets. Inserting or deleting one or two bases shifts the reading frame from that point onward, altering all subsequent amino acids. This is called a frameshift mutation.