Molecular Basis of Inheritance MCQs for NEET — Botany Questions with Answers

The general features of genetic code are:-

(i) The genetic code is written in linear form, using the ribonucleotide bases that compose mRNA molecule as letters.

(ii) Each word of codon consists of three letters, i.e, the codon is triplet.

(iii) The genetic code inside the cell medium is said to be non-ambiguous.

(iv) The code is degenerate, i.e, a given amino acid can be Specified by more than one codons.

(v) The codon contains ‘start’ and ‘stop’ signals.

(vi) The code is said to be commaless.

(vii) The code is non-overlapping.

In DNA molecule the adjacent deoxy ribonucleotides are joined in a chain by phosphodiester bridges or bonds, which link the 5’ carbon of deoxyribose of one mononucleotide unit with 3’ carbon of deoxyribose of next mononucleotide unit. According to Watson and Crick DNA molecule consists of two such polynucleotide chains wrapped helically around each other, with the sugar phosphate chain on the outside and purine and pyrimidine on the inside of helix. The two strands run antiparallely, ie, one strand has phosphodiester linkage in 5’ → 3’ direction while other strand has phosphodiester linkage in 5’ → 3’ direction. Chargaff (1950) suggested that despite wide compositional variations exhibited by different types of DNA the total amount of purines equaled the total amount of pyrimidines (A + G = T + C).

The group of nucleotides that specifies one amino acid is a code word or codon. The nucleotides of mRNA are arranged as a linear sequence of codons, each codon consisting of three successive nitrogenous bases. Three codons UAG, UAA and UGA are the chain stop or termination codons. They do not code for any of the amino acids.

In most organisms AUG codon is the start or initiation codon, ie, the polypeptide chain starts either with methionine or N-formylmethionine.

Leucine – UUA, UUG, CUU, CUC, CUA, CUG

Alanine – GUC, GCC, GCA, GCG

GUU – Valine

UCA – Serine

Telomeres are ends of chromosome, have repetitive DNA sequences and are stable and resistant to exonuclease digestion hence, essential for chromosome stability.

Transcription factor is molecular basis of organ differentiation.

In eukaryotic cells, DNA accommodated by super-coiling in nucleosomes.

TATA box is present in eukaryotic promoter region. It has a resemblance with pribnow box of prokaryotes. TATA box was identified by Dr. Hogness and so, it is called as Hogness box. It is a 7 bp long region located 20 bp upstream to the start point. During the process of transcription the RNA polymerase (a holoenzyme which has a core unit and a sigma factor for proper initiation of transcription) binds to TATA box due to which DNA assumes a saddle like structure at this place.

Differentiation of organs and tissues in a developing organism, is associated with differential expression of genes. In regulation of gene expression the chromosomal proteins play important role. The chromosomal proteins are of two types histones and non-histones. The regulation of gene expression involves an interaction between histones and non-histones.

In 1953 James Watson and Francis Crick suggested that in a DNA molecule there are two polynucleotide chains arranged antiparallel or in opposite directions.

The steroid hormone receptor protein complex activate transcription of target gene by binding to specific DNA sequence.