Download DNA PPT - McKinney ISD Staff Sites

In 1953, Watson and
Crick recognize that DNA
is a double-helix.
X-ray crystallography
image from Franklin
that provides clue
to DNA structure
The Components and Structure of DNA
•
DNA is in the shape of a twisted ladder,
called a double helix.
– The sides of the DNA are
made up of
1. Deoxyribose (sugar)
2. Phosphate group (links the
deoxyribose together)
– The “rungs” of DNA are made
up of bases
1.
2.
3.
4.
Adenine
Cytosine
Guanine
Thymine
Nucleotides always
“Base Pairs”
pair together. Purines
Pyrimidines
In 1949,
Chargaff
determined
that their were
equal parts A
and T, and
equal parts of
G and C
Adenine
Guanine
Thymine
Cytosine
Base Pairing
DNA Replication
• Helicase “Hacks” the
two strands open at
the hydrogen bonds.
• The DNA molecule
separates into two
strands
• DNA Polymerase
“pastes” matching
nucleotides on each
half of the “unzipped”
DNA.
2. DNA Polymerase
“reads” the
nucleotide base
sequence and
“pastes” the
correct nucleotide
to the growing
strand.
1. Helicase
“Hacks” the DNA
strands apart by
breaking the
hydrogen bonds
between the
nitrogen bases.
Old Strand
Old Strand
DNA replication is “SemiConservative.” DNA has one
old strand and one new strand
after replication is complete.
New Strands
• Amount of DNA varies per organism
– Bacteria have ~600,000 base pairs their
genomes. (A genome is an organism’s
complete set of DNA.)
– Humans have ~3,000,000,000 base pairs in
our genome.
– http://en.wikipedia.org/wiki/Genome
• Each human chromosome contains 50250 million base pairs.
This single-celled organism, Amoeba
dubia, has a larger genome than you do.
Chromosome Structure
• DNA is long.
– E. coli bacterium is about 2 μm
in length, yet it contains about
1.6 m of DNA.
– A single human cell contains
~1.8m of DNA!
(There is enough DNA in your body to
stretch from here to the moon and
back 70 times!!)
• Chromosomes are supercoils of DNA
– Double-stranded DNA coils around histone
proteins, called chromatin
– Chromatin forms coils, and then those coils
form coils again - supercoils
Genes
• Genes are the regions of DNA that are
instructions for making proteins (a few
make RNA).
• Humans have 20,000-25,000 genes.
• Only about 2% of our DNA is genes
– The noncoding regions function to provide
chromosomal structural integrity and to
regulate where, when, and in what quantity
proteins are made.
• Compare genes:
http://en.wikipedia.org/wiki/Gene