NEET Practice Questions (MCQs) with Answers & Solutions

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

Haploid plants can be produced in large number by anther and ovary cultures. Haploids may be useful for isolation of mutants, since, even recessive mutant alleles will be expressed in the mutagen treated generation itself. Desirable mutants may be selected at the haploid level and their chromosome number may be doubled to obtain homozygous mutant lines in a single generation.

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.

Tetracycline inhibits the interaction between tRNA and mRNA. Thus, prevents protein systhesis.