1. DNA function and structure

2. History Francis Crick and James Watson first described the structure of DNA in 1953. They received the Nobel Prize for this discovery.

3. DNA has to be packed tightly DNA is very long – 1.8 meters per cell To fit in nucleus must be wound tightly Histones – “packing protein” – DNA winds around like thread on spool – Also involved in gene regulation

4. Chromosomes in nucleus - nucleus protects genetic information Two strands linked together by hydrogen bonds DNA coils and folds To shorten into chromosomes A gene is a specific sequence of nucleotides located in a particular position on a particular chromosome that contains the information for specific proteins

5. DNA Stores and transmits genetic info that tells cells which proteins to make and when to make them Long chain of nucleotides Sequence of nucleotides different in every species Sequence of nucleotides “code” for the amino acid sequence for making proteins What is a gene?

6. DNA sequence of every species is different! Human karyotype Mouse karyotype

7. Structure of DNA a long string of nucleotides Many monomers linked together monomer = nucleotide Nucleotide consists of 3 parts 1. deoxyribose (5 carbon sugar) 2. phosphate group 3. nitrogen-containing base

9. Nitrogen base May be one of four – Adenine, A – Guanine, G – Cytosine, C – Thymine, T adenineguanine cytosine thymine Purines 2 Carbon rings Pyrimidines 1 carbon ring Phosphate group deoxyribose

10. DNA shape Double Helix Like a twisted rope ladder or spiral staircase The stairway's railings are composed of sugars and phosphates (THE BACKBONE) hydrophilic interacts with aqueous environment of cell The rungs contain the base pairs:

11. Base Paring Rules Nitrogen bases of each strand form bonds to keep strands together – Hydrogen bonds ALWAYS FOLLOW THIS PATTERN A-T (2 hydrogen bonds) C-G (3 hydrogen bonds) purine always bonds with pyrimidine (so equal length between strands)

12. COMPLEMENTARY STRANDS One strand of DNA is the mirror image of the other Base pairs are described as being complementary

13. Anti parallel strands Strands run in opposite directions. 5’ end (free phosphate) 3’ end (free sugar)