1. Chapter 12: DNA

2. ∗ DNA has 3 functions:
∗ Storing information
∗ Copying information
∗ Transmitting information
12.1 The Role of DNA

3. ∗ DNA – deoxyribonucleic acid
∗ Nucleotides – monomers that make up a DNA
molecule
∗ 3 parts:
∗ 5 Carbon sugar (deoxyribose)
∗ Phosphate group
∗ Nitrogenous base
∗ Adenine (A)
∗ Guanine (G)
∗ Cytosine (C)
∗ Thymine (T)
12.2 The Structure of DNA

4. ∗Edwin Chargaff (1949)
∗Chargaff’s Rule
∗[A]=[T]
∗[C]=[G]
Solving the Structure of DNA
Adenine Thymine Guanine Cytosine
35%
45%

5. ∗ Rosiland Franklin used X-ray diffraction to visualize
DNA structure (1952).

6. ∗ Watson and Crick were the
first to model DNA as a
double helix in 1953.

7. ∗ All the previous discoveries show us the structure of
DNA and how DNA can function as a carrier of genetic
information.
∗ Characteristics of the double helix model:
∗ Antiparallel strands
∗ Hydrogen Bonding
∗ Base Pairing
The Double Helix Model

8. Antiparallel Strands
∗Run in opposite directions
Base Pairing
∗Bases are held together by
hydrogen bonds.
Base Pairing
∗A bonds with T, and C bonds
with G
∗ Complimentary base pairs
hydrogen bond covalent bond

9. ∗ If the sequence of bases on one strand of a DNA
molecule is TCGAACTGA, the sequence on the other
(complimentary) strand is:
Practice Base Pairing

10. ∗ Why does DNA replicate?
(Hint: Think back to Mitosis)
∗ DNA is replicated in the S phase of the cell cycle, before
the cell divides.
12.3 DNA Replication

11. ∗ Step 1
∗ The DNA double helix
unwinds
∗ DNA helicase (enzyme).
∗ breaks the H bonds
between the bases.
∗ The areas where the
double helix separates are
called replication forks.
Copying the Code

12. ∗ Step 2
∗ DNA polymerase (enzyme)
moves along each DNA strand
adding complimentary bases
according to the base pairing
rules.
∗ DNA polymerase also
proofreads the DNA molecule
to reduce errors.

13. ∗ Step 3
∗ The process continues until
all of the DNA has been
copied.
∗ DNA polymerase detaches.

14. ∗ This process produces two DNA molecules each
composed of one new and one original strand.
∗ Both DNA molecules produced are identical to each
other.
∗ DNA replication takes place at many points on a
eukaryotic chromosome.
∗ Allows replication to happen more quickly.