Deoxyribonucleic acid (DNA): nucleotides building blocks (AGCT) stringed together.
4 types of nucleotides building blocks AGCT: Adenine, Guanine, Cytosine and Thymine.
A and G are purines (bigger), T and C are pyrimidines.
DNA double-helix: 2 strings of poly nucleotide chains.
The two chains are complimentary to each other, where an A always pairs with a T (and vice versa) in the other string, and a C paris with a G (and vice versa).
The two chains form a twisted double-helix shape (like a revolving ladder), where each step is an A-T or C-G pair.
A-T pairs are connected via 2 hydrogen bonds, where as C-G forms 3 hydrogen bonds.
5’ and 3’ end: each chain has a direction
One end of the chain has an unreacted phosphate group at carbon 5 of the nucleotide, called 5’end.
The other end has an unreacted -OH group at carbon 3 of the nucleotide, called 3’ end.
DNA sequence is written from 5’ to 3’- a positive or + strand. Its reverse compliment generate the sequence of the paired chain - the negative strand (also from 5’ to 3’).