Molecular Basis of Inheritance

Key idea Genetic code is a sequence of nucleotides in nucleic acid (DNA or RNA) that determine the amino acid sequence during protein synthesis.

Genetic codes for arginine are CGU, CGC, CGA and CGG.

CAU and CAC code for histidine. CAA and CAG code for glutamine. AGU and AGC code for serine. AAC codes for asparagine. GAU, GAC code for Aspartic acid. GAA code for glutamic acid.

Key idea The content of the human genome is commonly divided into coding and non-coding DNA sequences. Coding DNA are those sequences that can be transcribed into mRNA and translated into protein, they occupy only a small fraction of genome. Non-coding DNA sequences do not encode proteins.

Statement in option (b) is wrong. The correct form of statement is "less than $2 \%$ of the genome codes for protein".

Note In most of organisms more than $98 \%$ of human genome is composed of non-coding DNA (or Junk DNA).

Gene library or DNA library has collection of cDNA only. It is a cloned/copy DNA of cells/tissues, organs of an organism in a preserved form for future use.

Key idea The synthesis of RNA (transcription) in prokaryotes utilises a DNA dependent RNA polymerase to catalyse the bacterial RNA's. It complete in three steps - 1. Initiation 2. Elongation 3. Termination.

In prokaryotes, transcription of all types of bacterial RNA is catalysed by a single DNA dependent RNA polymerase in three steps.

Initiation It involves binding of RNA polymerase with the promoter site by associating with a initiation or sigma factor.

Elongation This step involves elongation of RNA chain as the RNA polymerase travel in $5^{\prime} \rightarrow 3^{\prime}$ direction. This step is characterised by dissociation of '$\sigma$' initiation factor from RNA polymerase.

Termination In this step, RNA polymerase on reaching termination region separates and RNA falls off from transcription unit. This step is characterised by binding of termination or rho ($\rho$) factor with RNA polymerase, which marks termination of transcription.

Both the assertion and reason are true, but reason is not the correct explanation of assertion. In eukaryotes, transcription, i.e. synthesis of RNA from DNA, occurs inside nucleus, because the genetic material DNA is enclosed inside the nuclear membrane in eukaryotes whereas, in the prokaryotes like bacteria, their genetic material-DNA remains suspended within the cytoplasm, thus in prokaryotes the process of transcription and translation occurs in cytoplasm.

The codons of glycine are GGU, GGC, GGA, GGG. A genetic code is the smallest unit to code one amino acid. This genetic code is defined as nucleotide sequence of nitrogenous bases, which specifies the amino acid sequence in a polypeptide molecule.