DNA has three main functions: storing genetic information, copying that information during cell division, and transmitting the information from parent to offspring. DNA is made up of nucleotides containing a sugar, phosphate, and one of four nitrogenous bases: adenine, guanine, cytosine, and thymine. The structure of DNA was discovered to be a double helix with the bases on each strand bonding with their complement on the other strand (A pairs with T and C pairs with G). DNA replication copies the DNA through unwinding of the helix, addition of complementary bases by DNA polymerase, and production of two identical DNA molecules, each with one original and one new strand.

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.