DNA Structure
(“transforming principle”)
Human Genetics
Chp. 9
DNA Structure

A gene is a long
section of a DNA
molecule whose
sequence of building
blocks specifies the
sequence of amino
acids in a particular
protein.


Genes combine to
form amino acids as
letters combine to
form words.
Amino acids make
proteins
DNA Structure

DNA shape is a double helix

View from the side

Partially unwound double helix so you can see components
Views from the top
Model
X-Ray
Photo-51
DNA Structure (Where are they?)
DNA composed of
nucleotides
1. Sugar (deoxyribose)
2. Phosphate group
3. Nitrogenous bases
1. Purines
1. Guanine (G)
2. Adenine (A)
2. Pyrimidines
1. Cytosine (C)
2. Thymine (T)
DNA Structure



A 5 C sugar and a
phosphate group form
the backbone
DNA is directional
Antiparallelism

the head to tail
arrangement of the 2
entwined chains of DNA
double helix
DNA Structure

Nitrogenous bases
 A,
T, C, & G
 make up the rungs on
the ladder
Complementary Base Pairing


Bases held together with
Hydrogen bonds
Guanine pairs with Cytosine


Triple bond
Adenine pairs with Thymine

Double bond
DNA Structure
 Minor
Groove
 Major Groove
 binding
proteins
interact with
DNA in the
major groove b/c
backbone isn’t in
the way
DNA Structure

Chromosomes – not just DNA!
1/3 DNA
 Histone proteins
 Other DNA binding proteins
 also a small amount of RNA


All together the chromosome material is called
Chromatin
DNA Structure
3D Video Clip (Click next 4 times)



A single molecule
of DNA can be 1
in. long
How does it fit
into a space that
is 1 millionth that
size?
Histones

proteins that
DNA coils
around
DNA Structure
1. 8 Histones
2. DNA
3. “linking” histone

Nucleosome
A unit of the chromatic
structure
GREAT DIAGRAM
(FIG. 9.11) ON PG 179
Clicker ?’s 7-13
DNA ReplicationPreserves genetic information
?
S phase of Interphase
 Gives each new cell a complete set of operating
instructions
 5’ to 3’ direction only
 3 Hypothesized mechanisms for DNA
Replication

DNA Replication (cont.)
Semiconservative
Conservative
Dispersive
Each new molecule
conserves half of
the original double
helix
One double helix
specifies creation of
a second double
helix
Double helix
shatters into pieces
that then synthesize
new DNA
Proved by Meselson
and Stahl
Marked DNA with
14N
2nd generation DNA
had ½ 14N and ½ 15N
Replication Technology

PCR- Polymerase Chain Reaction
Uses DNA Polymerase to rapidly produce millions of
copies of a specific DNA sequence of interest.
 Perhaps the most successful technology to ever
emerge from LIFE SCIENCE!!!
 Many Uses

 Forensics
blood, convict, exonerate false accusations
 Agriculture,

Vet., Medicine, Env. Sci.,
Microorganisms, viruses, parasites…