Biology : Molecular Basis of Inheritance

Transfer RNA (t-RNA) constitute about 10-20% of total cellular RNA. Since t-RNA are difficult to be separated by ultra- centrifugation, they are also called as soluble RNA (s-RNA).

Uracil is absent in DNA. It is present in RNA, instead of thymine. 

In DNA, adenine and guanine are purines and thymine and cytosine are pyrimidines.

In RNA, uracil and cytosine makes pyrimidine.

DNA is made up of double helix of two complementary strands. Both the strands get seperated during replication. Each strand of the original DNA molecule then serves as a template for the production of its counterpart, hence, a process is known as semi- conservative replication.

DNA synthesis or replication always proceeds in 5' $\to$3' direction because DNA polymerase acts on the 3'- OH of the existing strand for adding the free nucleotides.

DNA replication is the process of forming a copy of DNA. Transcription is the formation of RNA over DNA template. They both occur in nucleus as the required material DNA and RNA are present in the nucleus.

Translation is the process of protein synthesis. It is separated from transcription in both space and time. It prevents the intermixing of raw materials, protect DNA from respiratory enzymes and ribosomal machinery from nuclease.

Mutation is present in dominant condition because dominant mutant gene can express in both homozygous and heterozygous condition. While recessive gene can express only in homozygous condition.

Uracil is absent in DNA. It is present in RNA, instead of thymine. 

In DNA, adenine and guanine are purines and thymine and cytosine are pyrimidines.

In RNA, uracil and cytosine makes pyrimidine.

G.W. Beadle and E.L. Tatum demonstrated by the biochemical mutation experiment in Neurospora that genes express themselves through synthesis of enzymes. They proposed a concept called "one gene-one enzyme hypothesis".

Intrans are DNA sequence lying within a coding sequence, i.e. Exons but not usually encoding cell product and resulting so called split genes cistron is a segment of linear DNA encoding a specific and functional product, usually protein.

There are following three types of cellular RNA

(1) Transfer RNA or soluble RNA

(2) Messnger RNA or template RNA

(3) Ribosomal RNA

Transfer RNA (t-RNA) and messenger RNA (m-RNA) are synthesized on DNA template of chromosomes while ribosomal RNA (r-RNA) is derived from nucleolale DNA.

DNA has deoxy ribose pentose sugar and four nitrogenous bases i.e. Adenine (A), Guanine (G), both are purines; Cytosine (C) and Thymine (T), both are pyrimidines. 

RNA has ribose pentose sugar and four nitrogenous bases as in DNA except Uracil (U) in place of Thymine (T).