DNA Structure

The human cell has 2 sets of 23 chromosomes, in total 46 chromosomes.

Before cell division, DNA duplicates and you have two sister chromatids attached by a centromere.

DNA Structure

• Structure of DNA discovered by James Watson and Francis Crick
• Rosalind Franklin used X-ray diffraction to help determine structure of DNA
• DNA is composed of nitrogenous bases, deoxribose sugar and phosphate=nucleotide
• Sugar and phosphates form the backbone of the helix (spine of the ladder)
• Nitrogenous bases from one side of the ladder bond to nitrogenous bases on the other side
• They are bonded by hydrogen bonds which are weak bones between a positive hydrogen molecule and a negative charge on an electronegative nitrogen or oxygen molecule
• The four nucleotides are adenosine, guanine (purines) and cytosine and thymine (pyrimidines).
• Adenosine complimentary bonds to Thymine
  
• Guanine complimentary bonds to cytosine