1. Ch. 16 Warm-Up Draw and label a nucleotide.
Explain the semiconservative model of DNA replication.
What is the complementary DNA strand to:
DNA: A T C C G T A T G A A C

2. Chargaff’s Rules: If cytosine makes up 21% of the nucleotides, then adenine would make up ___ % ?
42%
58%
29%

3. THE MOLECULAR BASIS OF INHERITANCE
Chapter 16

4. What you must know The structure of DNA.
The major steps to replication.
The difference between replication, transcription, and translation.
The general differences between the bacterial chromosome and eukaryotic chromosomes.
How DNA is packaged into a chromosome.

5. Edwin Chargaff (1947) Chargaff’s Rules:
DNA composition varies between species
Ratios:
%A = %T and %G = %C

6. Rosalind Franklin (1950’s)
Worked with Maurice Wilkins
X-ray crystallography = images of DNA
Provided measurements on chemistry of DNA

7. James Watson & Francis Crick (1953)
Discovered the double helix by building models to conform to Franklin’s X-ray data and Chargaff’s Rules.

8. Structure of DNA DNA = double helix “Backbone” = sugar + phosphate
“Rungs” = nitrogenous bases

9. Structure of DNA Nitrogenous Bases Pairing: Adenine (A) Guanine (G)
Thymine (T)
Cytosine (C)
Pairing:
purine + pyrimidine
A = T
G Ξ C
purine
pyrimidine

10. In analyzing a number of different bases in a DNA sample, which result would be consistent with base pairing rules?
A=G
A+G=C+T
A+T=G+T
A=C
G=T

11. Structure of DNA
Hydrogen bonds between base pairs of the two strands hold the molecule together like a zipper.

12. Structure of DNA
Antiparallel: one strand (5’ 3’), other strand runs in opposite, upside-down direction (3’  5’)

15. DNA Comparison Double-stranded Circular One chromosome In cytoplasm
Prokaryotic DNA
Eukaryotic DNA
Double-stranded
Circular
One chromosome
In cytoplasm
No histones
Supercoiled DNA
Double-stranded
Linear
Usually 1+ chromosomes
In nucleus
DNA wrapped around histones (proteins)
Forms chromatin

16. Problem:
How does DNA replicate?

17. Replication: Making DNA from existing DNA
3 alternative models of DNA replication

18. Replication is semiconservative

19. DNA Replication Video
&feature=related

21. DNA polymerase DNA ligase Nucelotides Okazaki fragments primase
A biochemist isolates and purifies the molecules needed for DNA replication. When she adds some DNA, replication occurs, but each DNA molecule is a normal strand paired with segments of DNA a few hundred nucleotides long. What has she probably forgotten?
DNA polymerase
DNA ligase
Nucelotides
Okazaki fragments
primase

22. Major Steps of Replication:
Helicase: unwinds DNA at origins of replication
Initiation proteins separate 2 strands  forms replication bubble
Primase: puts down RNA primer to start replication
DNA polymerase III: adds complimentary bases to leading strand (new DNA is made 5’  3’)
Lagging strand grows in 3’5’ direction by the addition of Okazaki fragments
DNA polymerase I: replaces RNA primers with DNA
DNA ligase: seals fragments together

23. 1. Helicase unwinds DNA at origins of replication and creates replication forks

24. 3. Primase adds RNA primer

25. 4. DNA polymerase III adds nucleotides in 5’3’ direction on leading strand

26. Replication on leading strand

27. Elongation of the leading strand during DNA synthesis…
Progresses away from the replication fork
Occurs in the 3’ 5’ direction
Produces Okazaki fragments
Depends on DNA polymerase
Does not require a template strand

28. Leading strand vs. Lagging strand

30. BioFlix: DNA Replication
io/bioflix/bioflix.htm?8apdnarep