1. DNA: The Genetic Material
Chapter 14

2. Frederick Griffith (1928)

3. Avery, MacLeod & McCarty (1944)

4. Hershey & Chase (1962)

5. Rosalind Franklin & Maurice Wilkins

6. Erwin Chargaff

7. James Watson & Francis Crick

8. Messelson & Stahl

9. Messelson & Stahl

10. DNA Structure DNA is a nucleic acid
building blocks of DNA are nucleotides
deoxyribose (5-carbon sugar with –OH at the 3’ C)
phosphate group (PO4) attached to the 5’ C
nitrogenous base attached to the 1’ carbon
adenine, guanine, thymine, cytosine
A, G = purines
T, C = pyrimidines

13. DNA Structure Nucleotides bond together to form a chain
called phosphodiester bond
btwn the PO4 of one nucleotide and the 3’ –OH of the next nucleotide
chain of nucleotides has a 5’ to 3’ orientation

15. DNA Structure DNA double helix consists of:
2 sugar-phosphate backbones
nitrogenous bases toward the inside
bases form H bonds with complementary bases on opposite sugar-phosphate backbone

17. DNA Structure The two strands are antiparallel to each other
one is oriented 5’ to 3’, the other 3’ to 5’
strands wrap around each other to create the helical shape

19. DNA Replication Occurs during S phase
Mechanism of DNA replication is the semiconservative model
each strand of DNA acts as a template for the synthesis of a new strand

21. DNA Replication Overview

22. DNA Replication Includes: Initiation Elongation Termination
begins at an origin of replication
Elongation
new strands of DNA are synthesized
Termination
different in proks and euks

23. Prok vs. Euk DNA Replication
Chromosome of a prokaryote is a circular molecule of DNA
replication begins at 1 origin of replication and proceeds in both directions around the chromosome
Euk chromosomes are larger
replicated from multiple origins of replication

25. DNA Replication Enzymes helicase unwinds helix
DNA gyrase relieves torsional strain
single-stranded binding prots. (ssb’s) hold the unwound helix open
DNA primase creates RNA primer
DNA polymerase III (pol III) adds nucleotides to the 3’ end of new DNA behind primer

27. DNA Replication DNA replication is semidiscontinuous
DNA pol III only adds nts to the 3’ end of the growing strand strand
leading strand is synthesized continuously
lagging strand is synthesized discontinuously creating Okazaki fragments

29. DNA Replication DNA polymerase I (pol I) replaces RNA primers
DNA ligase links Okazaki fragments on lagging strand

31. Eukaryotic DNA Replication
Synthesizing the ends of euk chromosomes is difficult because of lack of a primer
With each round of DNA replication, the linear euk chromosome becomes shorter

33. Eukaryotic DNA Replication
8) telomerase
produces telomeres (repeated DNA sequence on the ends of euk chromosomes)
contains an RNA region that is used as a template so a DNA primer can be produced

35. DNA Replication Review

36. DNA Repair
Mistakes during DNA replication can lead to changes in the DNA (DNA damage)
damaged often caused by chemical or physical agents called mutagens
repair mechanisms may be used to correct these problems

37. DNA Repair

38. DNA Repair Mechanisms can be: specific
targeting a particular type of DNA damage
Ex: thymine dimers & photorepair

40. DNA Repair non-specific
able to repair many different kinds of DNA damage
excision repair to correct damaged or mismatched nitrogenous bases