2. Molecular Genetics

3. DNA STRUCTURE

4. I) DNA Structure DNA Structure according to the model proposed by Watson and Crick  DNA consist of two strands of nucleotides  each nucleotide contains a: deoxyribose sugar phosphate group nitrogen base  all are covalently bonded together A) DNA STRUCTURE

5. I) DNA Structure each strand of DNA has a backbone of sugar and phosphates groups.  the nitrogenous bases stick out from the backbone of each DNA strand the two strands of DNA form a structure that resembles a twisted ladder.  the base pairs are the rungs of the ladder  the sugar-phosphate backbone are the struts.  the twisted ladder is called a double helix the double helix twists in a clockwise direction A) DNA STRUCTURE

7. Side Note: Chargaff's Rule of Base Pairing A) DNA STRUCTURE

8. Side Note: Chargaff's Rule of Base Pairing whatever the amount of adenine (A) in the DNA of an organism, the amount of thymine (T) is the same  similarly, whatever the amount of guanine (G), the amount of cytosine (C) is the same. the C+G : A+T ratio varies from organism to organism among the prokaryotes),  within the limits of experimental error: A = T and C = G. Relative Proportions (%) of Bases in DNA OrganismATGC Human30.929.419.919.8 Chicken28.829.220.521.5 Grasshopper29.3 20.520.7 Sea Urchin32.832.117.717.3 Wheat27.327.122.722.8 Yeast31.332.918.717.1 E. coli24.723.626.025.7 A) DNA STRUCTURE

9. I) DNA Structure in the DNA molecule, the bases of one DNA strand are paired with bases in the other strand.  a purine is always paired with a pyrimidine adenine (a purine) is always paired with thymine (pyrimidine) guanine (a purine) is always paired with cytosine (a pyrimidine)  this type of pairing is called complementary base pairing  hydrogen bonds (between A-T and G-C) hold the double helix together.  hydrogen bonds are weak but because there is a lot of them the double helix is very stable A) DNA STRUCTURE

10. Important! T and A go together C and G go together Never any other combo, this is consistent between all species A) DNA STRUCTURE

12. I) DNA Structure the sequence of bases on any one strand of DNA can vary greatly between species.  the opposite strand will always have the complementary sequence of bases.  the two strands of nucleotides are antiparallel. they run in parallel but in opposite directions to one another.  one strand will have a 5’ carbon and phosphate group at one end and a 3’ carbon and the hydroxyl group of a deoxyribose sugar at its other end.  the antiparallel strand will have the opposite. A) DNA STRUCTURE

13. 12 DNA by the numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun.

14. I) DNA Structure Question: What is the complementary strand? 5’-ATGCCGTTA-3’ 3’-TACGGCAAT-5’ A) DNA STRUCTURE

15. Phylogeny The proposed evolutionary history of a group of organisms or species by looking at mutations in DNA mitochondrial DNA (mtDNA) can be used to trace inheritance through the maternal line in mammals since the egg is only source of mitochondria. Research has lead to two interesting models about Homo Sapiens

16. Multiregional model This proposes that the different ethnic groups observed worldwide today would have begun their evolution between 1-2 million years ago. The groups interbred to some degree, so they didn’t form different species.

17. Monogenesis Model This proposes that Homo species moved out of Africa twice,first as Homo erectus and second as Homo sapiens between 100 000 and 200 000 years ago. Modern ethnic groups are all descendants of the second migration.

18. And the winner is... Currently there is more support for monogenesis model. mtDNA analysis support this more The greatest variety of mtDNA mutations exist in African ethnic groups  The population that has exist the longest will accumulate more mutations over time  Additionally, mtDNA from ethnic groups on other continents were traced back to Africa rather than each other.