WHY DOUBLE HELIX?
Sugar and phosphate groups form the backbone of the strand. The nitrogenous base of the two chains project inward pointed towards each other. The bases of the 2 chains are linked in the middle of the molecule by hydrogen bonds (like 2 lines of people holding hands). The key to understanding why DNA is a double helix is revealed by looking at the bases: only 2 base pairs are possible. In every DNA double helix, adenine (A) is paired with thymine (T) and guanine (G) is paired with cytosine (C). A cannot pair with C and G cannot pair with T because they cannot form proper hydrogen bonds (because the electron sharing atom are not pointed to each other). Example: A–H–T T–H–A T–H–A G–H–C C–H–G A–H–T T–H–A 1st 2nd strand strand H- hydrogen bond 2. RIBONUCLEIC ACID – long, single strand of nucleotides and is used by cells in making proteins using genetic instructions within DNA. In RNA, URACIL replaces thymine in pairing with adenine. V. VITAMINS – any organic compound required b
