1. DNA
Chapter 12

2. What is dna? A long molecule found in the nucleus of the cell
A type of nucleic acid
is made up of smaller subunits called nucleotides
joined into long strands by covalent bonds
Nucleotides are made up of:
5-carbon sugar (deoxyribose)
a phosphate group
A nitrogenous base (adenine, guanine, cytosine, thymine)

3. The nucleotides are joined together by covalent bonds formed between the sugar of one nucleotide and the phosphate group of the next.
The nucleotides can be joined in any order

4. Erwin Chargaff’s rule
Percentages of:
Adenine (A) = thymine (T)
Guanine (g) = Cytosine (C)
This rule was obeyed In all organisms.

5. Rosalind Franklin’s X-rays
Used a technique called x-ray diffraction
showed strands of DNA twisted around each other (in a helix)
Showed Dna is made up of 2 strands
Gave clues the nitrogenous bases are near the center of the DNA molecule

6. Watson and Crick: Double Helix Model
Double helix = twisted ladder or spiral staircase
Confirms Chargaff’s rule and Franklin’s X pattern
Explains that the two strands are held together by weak hydrogen bonds between nitrogenous bases
Antiparallel strands run in opposite directions
Nitrogenous bases only formed bonds with specific nitrogenous bonds (A-T and G-C). This is known as Base pairing