Molecular Basis Of Inheritance 5 - From Past 28 Years Questions Free MCQ

Genetic code is the relationship of amino acid sequence in a polypeptide chain and base sequence of mRNA. It includes adenine, guanine, cytosine and thymine.

In semi conservative replication of DNA in each replica one half is the old strand and the other half is a new strand synthesized over it.

Genetic code is triplet coding for one amino acid in a polypeptide chain. There are four different types of nucleotides - A,T,G, and C. Since a code is a triplet thus 64 (4×4×4) distinct triplet of bases determine the 20 amino acids. But out of 64 only 61 code for 20 amino acids. Three codons that do not code for any amino acids are terminator non sense codons (UAG, UGA and UAA). Still in 61 triplet codons there is an excess 41 codons and therefore more than one codon codes for same amino acid.

Nucleotide is a unit of DNA , which is formed of nitrogenous bases (urines & Pyrimidines), sugar (Pentose) & phosphate.

Central dogma of protein synthesis explains a unidirectional or one way flow of information from DNA to RNA (transcription) and from RNA to polypeptide (translation).

After one generation in 14N medium DNA of bacteria settled at a level intermediate between heavy and light bands due to semi conservative DNA replication.

Hargonind Khurana first deciphered the triplet codon of cysteine and valine.

Messelson and Stahl (1958) raised Escherichia coli on ammonium chloride having heavy isotope of nitrogen for several generations to study semiconservative replication of DNA.

In 1953 Wilkins obtained very fine X-ray crystallographic pictures of DNA from which Watson and Crick developed the double helix model of DNA.

A single strand of DNA would not possess complementary base pairs. Hence nitrogenous bases are unequal in number.

Protein synthesis occurs over ribosomes which are also referred to as protein factories.

Unwindase or helicase takes par t in separation of two DNA strands. In prokaryotes, helicase or unwindase is assisted by gyrase in this function.

All amino acids are specified by more than one codon (except Tryptophan and Methionine). Hence they are degenerate.

Hershey and Chase (1952) worked on Escherichia coli and conclusively proved that DNA is the genetic material.

The transforming chemical discovered by Griffith in his experiments with Pneumococcus, was confirmed as DNA by Avery, McLeod and McCarty.

The initiation codon is the codon which initiates the protein synthesis. They are AUG for methionine and GUG for valine.

DNA gyrase participates in the unwinding of DNA helix during replication.

Protein synthesis stops when a nonsense codon (UAA, UGA or UAG) reaches the amino acyl or A site.

During transcription, from the DNA template complementary mRNA is formed and thymine is replaced by uracil.

Lac operon is an inducible operon system which regulates genetic material. The genetic material remains switched off normally but becomes operational in the presence of inducer lactose.

The phenomenon of making DNA over RNA genome through enzyme reverse transcriptase is called reverse transcription or teminism.

Codons are 6 in number. Each codon possess 3 bases, each of which can undergo transition and transversion. (1 × 32 = 549)

The tautomer forms of nitrogen bases are immuno-tautomer instead of amino group (e.g. cytosine, adenine) or enol instead of the keto group (e.g. thymine, guanine).
Tautomers are organic compounds that are interconvertible by a chemical reaction called tautomerization. The concept of tautomers that are interconvertible by tautomerizations is called tautomerism. Tautomerism is a special case of structural isomerism and can play an important role in noncanonical base pairing in DNA and especially RNA molecules. 

If Escherichia coli bacteria grow in normal glucose medium and when transferred to a medium containing lactose, then the lac operon is induced.

The region of a gene, which becomes part of m-RNA and code for different regions of the proteins are called exons.