C ∫ G XII XII - - - - as complementary base pairing. The DNA double helix or duplex is held together by two forces, a ) Hydrogen bonding between complementary base pairs b ) Base-stacking interactions The complementary between the DNA strands is attributable to the hydrogen bonding between base pairs but the base stacking interactions are largely non-specific, make the major contribution to the stability of the double helix. . .
Types of RNA molecules Ribonucleic acids are similar to DNA. Cells contain up to eight times high quantity of RNA than DNA. RNA is found in large amount in the cytoplasm and a lesser amount in the nucleus. In the cytoplasm it is mainly found in ribosomes and in the nucleus, it is found in nucleolus.
RNA molecules are classified according to their structure and function into three major types i. Ribosomal RNA (rRNA) ii. Messenger RNA (mRNA) iii. Transfer RNA (tRNA) rRNA rRNA is mainly found in cytoplasm and in ribosomes, which contain % RNA and % protein.
Ribosomes are the sites at which protein synthesis takes place. tRNA tRNA molecules have lowest molecular weight of all nucleic acids. They consist of – nucleotides in a single chain. The function of tRNA is to carry amino acids to the sites of protein synthesis on ribosomes.
mRNA mRNA is present in small quantity and very short lived. They are single stranded, and their synthesis takes place on DNA. The synthesis of mRNA from DNA strand is called transcription. mRNA carries genetic information from DNA to the ribosomes for protein synthesis.
This process is known as translation Table . Difference between DNA and RNA DNA RNA It is mainly present in nucleus, mitochondria and chloroplast It is mainly present in cytoplasm, nucleolus and ribosomes It contains deoxyribose sugar It contains ribose sugar Base pair A = T. G ≡ C Base pair A = U. C ≡ G Double stranded molecules Single stranded molecules It's life time is high It is Short lived It is stable and not hydrolysed easily by