Introduction

NUCLEIC ACIDS

     PYRIMIDINES AND PURINES BASE

• Pyrimidines

Thymine and Cytosine are the smallest of the 4 bases. With only 1 ring in their structure.

Point to Remember!

*** In RNA, Thymine is replaced by Uracil ***

• Purines

Adenosine and Guanine are the biggest of the 4 bases. Their structure contains a pyrimidine ring + a smaller 5 sided ring. Therefore making a 2 ringed structure.

·      NUCLEOSIDE

•   A nucleoside consists of a nitrogenous base covalently attached to a sugar by glycosidic bond (ribose or deoxyribose) but without the phosphate group.
•  Nucleoside = Sugar + Base

NAME OF NUCLEOSIDES

·       NUCLEOTIDE

•  A nucleotide consists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups.
•   Nucleotide = Sugar + Base + Phosphate
•   A nucleotide is the basic unit that makes up DNA.
•    A singular nucleotide is made up of 3 components:

             1. A base (1 of 4 molecules = A, T, C or G)

             2. Five Carbon sugar (deoxyribose = DNA or ribose = RNA)

             3. Phosphate group (forms a bond between the sugar molecules in a 

                 DNA chain =  phosphodiester bond)

DEOXYRIBONUCLEIC ACID (DNA)

DNA 1° STRUCTURE

• Primary Structure: the sequence of bases along the pentose-phosphodiester backbone of a DNA molecule.
• Base sequence is read from the 5’ end to the 3’ end
• System of notation single letter (A, G, C, T)

DNA 2° STRUCTURE

            ·       Two anti-parallel polynucleotide chains wound around the same axis.

•       Sugar-phosphate chain wrap around the periphery.
•            Bases (A, T, G and C) occupy the core, forming complementary A-T and G-C (Watson-Crick base pair)
•         A-T are weaker than G-C because A-T comprised of 2 hydrogen bond, while G-C comprised of 3 hydrogen bond.

   
DNA 3° STRUCTURE

            ·    The three-dimensional arrangement of all atoms of a nucleic acid (supercoiling-further coiling and twisting of DNA helix).

•       Circular DNA: a type of double-stranded DNA in which the 5’ and 3’ ends of each stand are joined by phosphodiester bonds. 

      DNA 4° STRUCTURE

• ·       DNA double helical structures coil round histones.
• ·       DNA bound to histones forms nucleosome (10nm fibre)
• ·       Nucleosome contains 146 nucleotides
• ·       Nucleosome: any of the repeating globular subunits of chromatin consist of a complex of DNA and complex.
• ·       Histone: a protein, found associated with eukaryotic DNA.
• ·       Chromatin: DNA molecules wound around particles of histones in a beadlike structure.

     

       DENATURATION OF DNA 

•       Double helix unwinds when DNA is denatured.
• ·       Can be re-formed with slow cooling and annealing.

      RNA STRUCTURE

•       Typically single stranded and contains ribose as its pentose sugar and the pyrimidine uracil instead of thymine. An RNA strand can undergo significant intramolecular base pairing to take on a three-dimensional structure.
•       There are three main types of RNA, all involved in protein synthesis.
•        Although RNA is not used for long-term genetic information in cells, many viruses do use  RNA as their genetic material.