2.6 & 7.1 DNA & RNA
Structure Notes
IB Biology HL 1
Mrs. Peters
Spring 2015
DNA
 DNA: deoxyribonucleic
acid
 Molecular basis of
inheritance, genetic
material
DNA
 Structure discovered by
James Watson and
Francis Crick in April
1953
 their model was based
on Rosalind Franklin’s
x-ray data and Edwin
Chargaff’s nucleotide
data
RNA
 RNA: ribonucleic acid
 DNA “photocopy”
 leaves nucleus to make proteins
U1. Nucleic Acids


Ibbiologyhelp.com
Nucleic Acids: type of
macromolecule made up
of nucleotides
(monomers)
Two types:
 DNA:
Deoxyribonucleic Acid
 RNA: Ribonucleic
Acid
U1. Nucleotide Structure
 Nucleotide Structure


Phosphate group
Pentose Sugar



Nitrogen base



Ibbiologyhelp.com
DNA: deoxyribose
RNA: ribose
DNA (A,C,G,T)
RNA (A,C,G,U)
Held together by
covalent bonds
S1. Nucleotide Structure Diagrams
 Nucleotide Structure
 Draw and label a
nucleotide (in class)
Ibbiologyhelp.com
U2. DNA vs. RNA (In Class)
Feature
DNA
RNA
Strand
Double helix
Single strand
Pentose Sugar
Deoxyribose
Ribose
Nitrogen Bases
A, C, G, T
A, C, G, U
Nucleus only
Nucleus and
cytoplasm
Location
U3. DNA Structure
 Nitrogen Bases
 Purines: adenine (A),
guanine (G)
 Two rings
 Pyrmidines: cytosine
(C), thymine(T)
 One ring
U3. DNA Structure
 Complementary Base
Pairing:


A and T bonded by two
H bonds
C and G bonded by
three H bonds
U3. DNA Structure
 Two nucleotides are
bonded together in the
center by hydrogen
bonds forming a double
helix
 Sugar and phosphate
are covalently bonded,
forming the “backbone”
of each strand
U3. DNA Structure
 Double helix is made of
two separate strands
which are antiparallel




5’- 3’
3’-5’ (upside down)
5’ end: phosphate
group (PO43-)
3’ end hydroxide
group (–OH) attached
to sugar
U3. DNA Structure
 Draw and label a
diagram of the
molecular structure of
DNA
DNA Structure
Describe what is meant by the statement: “The
structure of DNA is described as a twisted
ladder.”
7.1 U2. Nucleosomes
Nucleosomes help to
supercoil DNA
8 histone proteins (octomer)
with DNA wrapped around
twice
H1(specific histone protein)
attaches the DNA to the
octomer
Linker DNA- short segment
of DNA connects one
nucleosome to another
Beyondthedish.wordpress.com
7.1 S1. Hershey and Chase
 1950’s Alfred Hershey and Martha Chase
studied viruses to determine if genetic
material was protein or DNA
 DNA contains phosphorous, proteins contain
sulfur
 Used radioactive isotopes of phosphorous-32
and sulfur-35 in T2 bacteriophages (virus)
which were injected into E. coli (bacteria)
7.1 S1. Hershey and Chase
Trial 1:
 Injected bacteria with T2 viruses that
contained sulfur-35 in protein coats (on the
outside) and normal DNA
 Used blender the gently shake the virus off
the bacteria
 Bacteria produced no radioactivity, virus had
the radioactive isotopes still attached
7.1 S1. Hershey and Chase
Trial 2:
 Injected bacteria with T2 viruses that
contained phosphorous-32 in DNA, normal
protein coats
 Used blender to gently shake virus off
bacteria
 Bacteria produced radioactive DNA
7.1 S1. Hershey and Chase
Conclusion:
DNA is the genetic material because the virus
DNA had radioactive phosphorous which
became present in the bacteria’s DNA
7.1 S1. Hershey and Chase
7.1 A1: Franklin and Wilkins
Rosalind Franklin was a research associate in
biophysics unit at King’s College in London.
Became skilled in techniques of
crystallography and X-ray diffraction while
researching other carbon compounds.
Created the sharpest X-ray diffraction images
of DNA in existence
Through rigorous analysis of the patterns, she
calculated the dimensions of the DNA helix
7.1 A1: Franklin and Wilkins
Maurice Wilkins worked in the biophysics unit at
King’s College also.
He also used X-ray diffraction to look at DNA
Shared Franklin’s diffraction pattern and
calculations to Watson, without Franklin’s
knowledge or permission, before she could
publish her findings.
7.1 A1. Franklin and Wilkins
Deductions made by
Franklin:
• Cross in the center
indicated a helix shape
• Angle of the cross
shape showed the
pitch of the helix
• Distance between
horizontal bars shows
the turn (3.4 nm apart)
Undsci.berkeley.edu
7.1 A1. Franklin and Wilkins
Deductions made by
Franklin:
• Distance between
middle of pattern and
top shows repeating
structure
• Distance is 0.34 nm
between repeats
DNA Structure Review
 What are the components of DNA?
 How is 6 ft of DNA stored in every cell?