1. Chapter 12 DNA: The Molecule of Heredity

2. Objectives Analyze the structure of DNA Determine how the structure of DNA enables it to reproduce itself accurately.

3. What is DNA? Genetic material Necessary for protein synthesis Determines an organism’s traits

4. Structure of DNA DNA is a polymer made of repeating subunits called nucleotides. Nucleotides:  Phosphate group  Simple sugar  A nitrogenous base: Purines:Pyrimidines:  Guanine (G) Cytosine (C)  Adenine (A) Thymine (T)

6. Watson and Crick DNA is made of two chains of nucleotides held together by nitrogenous bases Nitrogenous bases form hydrogen bonds  Complementary base pairs: A bonds with T C bonds with G The shape of DNA is called a double helix  Two strands twisted together

7. Nucleotide sequences Nucleotide arrange to form unique genetic sequences The more similar sequence the closer relation between organisms Used to determine evolutionary relationships

8. Nucleotides composed of  Pentose sugar  Phosphate  Nitrogenous base (A,T,C,G) Phosphates bond to the 3’ and 5’ carbons,… Nitrogenous bases bond to the 1’ carbon. Nucleotide Structure Review (Ch. 12)

9. Nucleotides – a simpler diagram Nitrogen bases 5-carbon sugar Phosphate group(s) Adenine Deoxyribose

10. Deoxyribose gives its name to DNA, ribose (shown on right) to RNA Ribose, C 5 H 10 O 5 Oxygens and hydrogens have been omitted... The carbons are numbered clockwise from the oxygen atom: Deoxyribose = a Sugar

11. Nitrogenous Bases Pyrimidines = single-ring structure  Thymine (T) & Cytosine (C) Purines = double-ring structure  Adenine (A) & Guanine (G)

12. What about Uracil Uracil - Similar in structure to thymine. Is nitrogenous base for RNA (ribonucleic acid)

13. Nitrogenous Base Pairing Purines are always paired with pyrimidines and vice versa. Each base has side groups that H bond with one another:  A is complementary to T (2 H bonds)  C is complementary to G (3 H bonds) These findings explain Chargaff’s earlier findings concerning equal amounts of Adenine and Thymine in DNA samples.

14. Chargaff measured the amount of each of the nucleotides in various tissues and organs... Pairing of Nucleotides: Chargaff’s Data Note the amount of adenine and thymine in each sample… Similarly, the amount of guanine and cytosine...

15. Two nucleotides: adenine and thymine Two hydrogen bonds between them... Adenine & Thymine

16. Cytosine and guanine are also connected by three hydrogen bonds Cytosine & Guanine

17. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BasePairing.gif

18. DNA Structure DNA structure similar to that of a ladder: Sugar phosphate backbone = sides of ladder Nitrogenous bases = rungs of ladder.

19. Note that the complementary strands are upside with respect to each other (antiparallel).

20. DNA is a polymer, made of nucleotide monomers DNA forms a double helix, two molecules spiraled DNA replicates itself with the help of polymerase enzymes DNA Replication

21. Nucleotides

23. DNA Replication A portion of the double helix is unwound by the enzyme helicase. DNA polymerase binds to one strand of the DNA and begins moving along 3' to 5' direction forming a new double helix  Forms the leading strand

24. DNA Replication DNA synthesis can only occur in the 5' to 3' direction. A second type of DNA polymerase binds to the other template strand as the double helix opens  Discontinuous segments (Okazaki fragments) DNA ligase I then stitches these together new strand  Forms the lagging strand

25. DNA Replication Results:  Chromosomes copied  Formation of two DNA molecules  New DNA strand is identical to the original DNA strand DNA replicates in interphase prior to mitosis and meiosis