DNA and RNA are nucleic acids. They form polynucleotide chains with a sugar – phosphate backbone, these are nucleotides that act as monomers and are joined together each nucleotide consists of a phosphate, pentose sugar and an organic nitrogenous base. The phosphate condenses with the pentose sugar by a phospdodiester bond, building up the chain. The bases stick out along the side, and since there are different types of nucleotides the bases can be in any order along the chain.
The nucleotides join together to form a polynucleotide chain
The structure of DNA
We have just learnt about nucleotides and well DNA is made up of four types that have different bases:
In DNA there are two strands of polynucleotide chains that are linked by Hydrogen bonds this occurs between the bases. Adenine pairs with Thymine forming two hydrogen bonds, and Cytosine pairs with Guanine forming three hydrogen bonds.
Adenine and Guanine are know as Purines which are double ring structures
Cytosine and Thymine are know as Pyrimidines which are single ring structures
The two strand are now twisted into a double helix, it is the arrangement of the bases and the bonds that form between them that makes DNA so stable. It is very important ar DNA’s function is to store genetic information. Because they are in a double helix with the bases attached to each other they are protected from most damage. In addition a purine must pair with a pyrimidine due to their sizes, so a small base will need to pair with a large bases to keep the same distance apart in the DNA strand.
Structure of RNA
Just like in DNA, RNA is made up of four nucleotide bases, adenine and guanine ( purines) and uracil and cytosine (pyrimidine), as you can see it is very similar to DNA the only difference it that uracil replaces thymine.
They produce single polynucleotide chains
There are three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA.
Messenger RNA ( mRNA) this is formed in the nucleus, and its a single chain twisted into a helix , its length and sequence varys. It is involved in protein synthesis
Transfer RNA (tRNA) this single chain is folded into a clover leaf shape. Involved in protein synthesis
Ribosomal RNA (rRNA) it is produced in the nucleolus and forms over half the mass of ribosomes.