1. Molecular Genetics

2. What is this stuff? Simply: DNA contains the instructions for making proteins in a cell DNA = Deoxyribonucleic Acid The genetic/hereditary material Referred to as a “blueprint” for life More of a “recipe”

3. DNA – The Genetic Material DNA contains our genes: Gene: A segment of DNA that codes for a specific protein DNA is packaged with proteins to form chromosomes DNA wraps around 8 histone proteins  nucleosomes Nucleosomes  large, coiled loops, held by scaffolding proteins Loops interact  Chromosomes

4. Why Study DNA? Medical purposes Producing better crops Controversial, downsides DNA Forensics Evolutionary relationships Many, many more........

5. A Brief History of DNA Hershey and Chase (1952) Bacteriophages: attach to cell and inject own genetic material Cell uses genetic material to make more viruses Labelled bacteriophage: Protein coat with 35 S DNA with 32 P Infect cells Agitate cells in a blender (shakes off bacteriophages) Centrifuge cells to separate from phage particles Only 32 P found in cells, not 35 S Conclusion: The active component of the bacteriophage that transmits the infective characteristic is the DNA. There is a clear correlation between DNA and genetic information.

6. DNA Review! Has shape of helix or corkscrew Is about 2 nm in diameter 2m of it in a nucleus!! Makes a complete helical turn ever 3.4 nm An awesome interactive review... http://learn.genetics.utah.edu/content/begin/tour/

7. The Structure of DNA DNA molecules consist of two polynucleotide chains The two chains, or strands, are twisted and arranged in a double-helix Ladder-like arrangement We will look at a single strand first

8. A Single Strand Composed of nucleotide building blocks Three main components A pentose sugar: deoxyribose A phosphate A nitrogenous base

9. Turn up the Base(s)!

10. Structure of deoxyribose

11. A Single Strand Composed of an alternating sugar- phosphate backbone: legs of ladder The bases stick into the middle:rungs of ladder The phosphate end is referred to as the 5’ (five prime) end Attached to Carbon 5 The opposite end is referred to as the 3’ (three prime) end (Carbon 3) Consists of millions of nucleotides

12. DNA Is Double Stranded Recall the double helix The legs of the ladder = sugar-phosphate backbone The rungs = bases How do single strands stick together?

13. 4 Types of Nitrogenous Bases DNA has 4 kinds of nitrogenous bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T) 2 Categories: 1)Purines: Two carbon rings Adenine and Guanine 2)Pyrimidines: One carbon ring Thymine and Cytosine

14. Bases are attracted to each other by hydrogen bonds Weak, but millions of them in a DNA molecule This is what holds the strands together When bonds form: Guanine always pairs with Cytosine – 3 bonds Adenine always pairs with Thymine – 2 bonds Base pairing is complimentary DNA Is Double Stranded – Hydrogen Bonds Hydrogen bonding between base pairs

15. DNA Is Double Stranded Chargaff’s Rule 1950 - Erwin Chargaff looked at percentages of bases in DNA samples 1:1 ratio of purines to pyrimidines Amount of G = C  They always pair Amount of A = T  They always pair

16. DNA Is Double Stranded Base pairing is complimentary: use one strand to predict the other Strands are anti-parallel: run in opposite directions The 3 ’ end terminates with the hydroxyl group of the deoxyribose sugar. The 5 ’ end terminates with a phosphate group

18. Finding the code... 5 ’ - ATGCCGTTA - 3 ’ 3 ’ - TACGGCAAT - 5’ By convention, only the 5’ to 3’ strand is written since the complementary strand can easily be deduced... Try this one... 5 ’ - TGGACGCTT - 3 ’ 3 ’ - ACCTGCGAA - 5’

19. DNA Shape: The Double Helix We use the analogy of a ladder that has been twisted into a helix Right Handed Helix: B-DNA, type generally found Left-Handed Helix: Z-DNA

21. 0.34 nm distance between base pairs (10 base pairs in 1 helical turn – 3.4 nm) width: 2nm Each cell has about 2 m of DNA. How does all this DNA fit into the tiny nucleus?

22. the DNA helix is coiled and long segments (200 nucleotides long) are wrapped around a complex of 8 histones (proteins) this bead-like structure is called a nucleosome DNA is negative (phosphate groups) and so is attracted to the positively charged histones the histones protect the DNA from breaking and tangling

23. nucleosomes are packed as a solenoid, a 30 nm fiber that has at least 5 nucleosomes strands together wound helically this arrangement of DNA (chromatin) makes it more compact and easier to accommodate in the relatively small nucleus

24. DNA (and protein) fibers are then further coiled (supercoiling) to form chromosomes a chromosome is one unbroken double-stranded DNA helix (only seen when they condense during cell division) Just before mitosis, 2 identical copies (sister chromatids) are visible, attached at a region called the centromere Packaging of DNA

25. V6/ Ending on a cooler note 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.

26. That’s it!

27. Homework... Answer DNA Handout Questions, Complete Build a DNA molecule Lab questions **DNA Extraction Lab Friday – Prelab questions p 230 of textbook.