Bio and chemistry

 RNA(Ribonucleic Acid) It is a single stranded polynucleotide.  By the action of RNA polymerase it is made in nucleus from one strand of DNA. protein synthesis is the primary function of RNA. RNA consists of nitrogenous bases, either purine (adenine or guanine) or pyrimidine (cytosine or uracil), sugar. (ribose) and phosphoric acid. Thymine (pyrimidine) is never pres- ent in RNA. There are three kinds of RNA 1.e. messenger  RNA (mRNA), transfer RNA (tRNA) and  ribosomal RNA (rRNA). mRNA takes the message from DNA to tRNA. Just one strand of DNA serves as a tem- plate for the synthesis of mRNA. tRNA also called soluble RNA (sRNA) reads the message and transfers amino  acids to the proper site on the rRNA. rRNA in ribosome of the endoplasmic  reticulum, synthesize protein from the  amino acids brought by tRNA.

 DNA(Deoxyribonucleic Acid) is a double stranded (double helix) polynucleotide. DNA consists of nitrogenous bases both, purines (adenine and guanine) and pyrimidines (cytosine and thyminc), sugar (deoxyribose) and phosphoric acid. • Uracil (pyrimidine) is not present in DNA. • In DNA the two strands are joined together through out the whole length of the molecule. DNA strands are complementary to cach other but run in opposite directions.The joining between the two strands Always Occurs between purines and pyrimidines and not between purines themselves or pyrimidines themselves. There is a rule, known as "the pairing rule" according to which adenine always joins thymine through three hydrogen bonds (A=T)) and guanine always join cytosine through three hydrogen bonds(G=C). A purine and a pyrimidine, which joins together to form DNA, is known as complementary pair of bases. Therefore adenine (A) and thymine (T) form one complementary pair and guanine (G) and cytosine (C) form t...