1. DNA: Discovery & Replication

2. Does DNA = genes?
DNA is in the nucleus DNA is in the nucleus of all species looked at each species has it’s own ‘amount’ of DNA Somatic cells have twice the DNA as gametes

3. Rosalind Franklin:
July 25, 1920 – April 16, 1958
Maurice Wilkins:
December 15, 1916 – October 5, 2004

4. Figure 14.3 The DNA Double Helix and Its Building Blocks
A nucleotide consists of three types of chemical groups: a phosphate, a sugar, and a nitrogen-containing base. DNA contains four types of nucleotides, varying only in the type of base found in them. DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase. The two strands are held together by hydrogen bonds between their complementary bases. (Inset) James Watson (left) and Francis Crick, with a model of the DNA double helix.

5. Figure 14.3 The DNA Double Helix and Its Building Blocks
A nucleotide consists of three types of chemical groups: a phosphate, a sugar, and a nitrogen-containing base. DNA contains four types of nucleotides, varying only in the type of base found in them. DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase. The two strands are held together by hydrogen bonds between their complementary bases.

6. Figure 14.3 The DNA Double Helix and Its Building Blocks
A nucleotide consists of three types of chemical groups: a phosphate, a sugar, and a nitrogen-containing base. DNA contains four types of nucleotides, varying only in the type of base found in them. DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase. The two strands are held together by hydrogen bonds between their complementary bases.

7. Figure 10.3C
Figure 10.3C A rope ladder model for the double helix
Twist 7

8. Figure 14.3 The DNA Double Helix and Its Building Blocks
A nucleotide consists of three types of chemical groups: a phosphate, a sugar, and a nitrogen-containing base. DNA contains four types of nucleotides, varying only in the type of base found in them. DNA consists of two complementary strands of nucleotides that are twisted into a spiral around an imaginary axis, rather like the winding of a spiral staircase. The two strands are held together by hydrogen bonds between their complementary bases.

9. Partial chemical structure
Figure 10.3D_2
Hydrogen bond
G C
T A
A T
Figure 10.3D_2 Three representations of DNA (part 2)
C G
Partial chemical structure 9

10. 5 end 3 end P HO A T C G OH 5 4 3 2 1 1 Figure 10.5B
Figure 10.5B The opposite orientations of DNA strands 10

11. 3C 5C 5C 3C

12. A parental molecule of DNA
Figure 10.4A_s1
A T
C G
G C
A T
T A
A parental molecule of DNA
Figure 10.4A_s1 A template model for DNA replication (step 1) 12

13. A parental molecule of DNA
Figure 10.4A_s2
A T T A A T
C G C G G C
G C G C C A
A T A T
Free nucleotides
T A T A
A parental molecule of DNA
The parental strands separate and serve as templates
Figure 10.4A_s2 A template model for DNA replication (step 2) 13

14. A parental molecule of DNA
Figure 10.4A_s3
A T T A A T
A T
A T
C G C G G
C G
C G C
G C G C C
G C
G C A
A T A T
A T
A T
Free nucleotides
T A T A
T A
T A
A parental molecule of DNA
The parental strands separate and serve as templates
Two identical daughter molecules of DNA are formed
Figure 10.4A-s3 A template model for DNA replication (step 3) 14

15. Figure 14.5 The Replication of DNA Is Semiconservative
In this overview of DNA replication, the template DNA strands are blue, and the newly synthesized strands are orange. One strand (blue) from the parent double helix is conserved in each newly made daughter double helix (blue and orange).

16. DNA polymerase molecule
Figure 10.5C 3
DNA polymerase molecule
This daughter strand is synthesized continuously 5
Parental DNA 5 3
Replication fork
This daughter strand is synthesized in pieces 3 5
Figure 10.5C How daughter DNA strands are synthesized 5 3
DNA ligase
Overall direction of replication 16

17. . helicase-unwinds DNA, req. ATP
b. single-stranded binding proteins-keep DNA from rebinding to self
c. origin of replication (1 in proks, multi in euks)
d. primase-synthesiaex RNA primer-short strand-where DNA polymerase attaches to strand
e. DNA polymerase III-open right hand: palm = active site; fingers = recognize bases
f. DNA polymerase I-knocks off RNA/makes DNA (lagging strand)
g. DNA ligase-makes phosphodiester bond-joins sugar phosphate backbone together at gaps (lagging strand)
Build-new DNA built off of template 3` end toward 5` end-only one strand has this orientation = leading strand
other strand = lagging strand= thread thru, add primer and work back toward earlier primer-okazaki fragments