 Double
helix
 Nucleotide
 Semiconservative replication
 DNA polymerase
 Chromatin
 Deoxyribonucleic
acid
(DNA) is a nucleic acid
 Composed of two
strands of DNA
 Shape is a DOUBLE
HELIX

Twisted ladder shape
formed by two strands
of DNA twisted around
each other
made up of
subunits called
NUCLEOTIDES
 Building blocks of
nucleic acids
 Three parts of
every DNA
nucleotide
Nitrogen base
 DNA
a five-sided sugar
(deoxyribose)
 a phosphate group
 a nitrogen base

phosphate
group
deoxyribose
Nitrogen base
phosphate
group
deoxyribose
 Four




nitrogenous bases
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
 Sugar
and phosphate
group stay the same,
nitro base changes
 Nitro bases form base
pairs


A-T
G-C
 Chargaff’s
Rule states
that the amount of
each G=C and A=T
Sugar and phosphate form “backbone” of DNA
and nitro bases form rungs of the ladder
 Hydrogen bonds join the bases in the center
 Strands run in opposite directions (antiparallel)


One runs 3’- 5’, other 5’- 3’
SEMICONSERVATIVE
REPLICATION: Parental
strands of DNA separate,
serve as templates, and
produce DNA molecules
that have one strand of
parental DNA and one
new strand
 DNA unwound and
unzipped by enzymes,
exposing the genetic
code
 Forms a replication fork

 DNA
POLYMERASE:
Enzyme responsible for
adding appropriate
nucleotides to the
growing strands of DNA


Enzyme reads A, places T
opposite it
Forms complimentary
strands on parent strands

Complimentary means
opposite
 For
eukaryotes,
multiple
replication sites
on DNA

We have multiple
strands of DNA that
is open-ended,
having a definite
beginning and end
 For
prokaryotes,
which have a
circular
chromosome, one
replication site
 CHROMATIN:
Relaxed
form of DNA in the
nucleus


DNA is wrapped around a
protein at multiple sites
Chromatin condenses to
form a chromosome
 From
unpacked to
packed



DNA
Chromatin (DNA +
protein)
Chromosome
Why “move”?
 Used for cell growth,
replacement, and sexual
reproduction
 Ensures that all cells
receive the exact amount
of chromosomes
 DNA itself is the
“instructions for proteins”

The Discovery of DNA
Rosalind
Franklin, 1951
 Took
an x-ray
diffraction photo of
DNA molecule to
understand it’s
structure
 James
Watson and
Francis Crick, 1953



Published a paper stating
that the structure of DNA
was a DOUBLE HELIX
Used Rosalind’s image to
discover shape
Won Nobel prize
 When
do we need new cells? Why would DNA
need to be replicated?
 What are the three parts of every nucleotide?
What makes DNA nucleotides different from each
other?
 What is the name of the sugar in a DNA
nucleotide?
 Form a complimentary strand for the following
parent strands:
1.
2.
ACGTTACCCCCATGGATG
CCTGACTTTACTTGGAAC
 Why
is DNA packed so tightly?
 How
is a prokaryotic chromosome different
from a eukaryotic chromosome?
 In your own words, explain Chargaff’s rule.
 Describe the structure of DNA using the
appropriate terms.