Download Chapter 13 PowerPoint Notes (DNA)

Honors Biology
Chapter 13
DNA Structure and
Function
Modified By: R. LeBlanc
10/’11
Early scientific discoveries. . .

Johann Friedrich Miescher (1868) discovered
“nuclein” later to be named DNA. Biologists
ignored his discovery for 75 years.

P.A. Levene (1920) discovered that there were 4
nitrogen base molecules found in DNA.

Fred Griffith (1928) while trying to find a vaccine
for pneumonia, he discovered the process of
transformation. He used two strains of pneumonia
bacteria: A harmless strain (R) with a “rough”
surface and a deadly strain (S) with a “smooth”
surface.
Griffith’s Experiment
What was the conclusion from this
experiment?
How was this possible? Could
it be TRANSFORMATION?
A Summary of Griffith’s
Experiment
This experiment clearly
demonstrated the presence of a
hereditary material & its ability
to be transferred from one
organism to another!
Which Substance (DNA or Protein)
Carried the Hereditary Information?

Oswald Avery (1944)
added proteindigesting enzymes to
cells, but
transformation
occurred anyway.
 DNA-destroying
enzymes stopped
transformation.
 So, what did Avery’s
experiment prove?

Most biochemists
ignored Avery’s work,
claiming that his
results probably only
applied to bacteria.
 Proteins were still
believed to be the
carriers of hereditary
information.
What runs the cell, DNA or proteins?

Researchers like
Delbruck, Hershey, &
Luria in the 1950’s
began using viruses
called bacteriophages
to study the transfer of
genetic information.
 These are made of
only two things:
• DNA
• Protein.
Bacteriophages: Valuable Tools in Finding the
Identity of the Hereditary Substance.
–genetic material
–viral coat
–sheath
–base plate
–tail fiber
bacterial
cell wall
plasma
membrane
cytoplasm
In the electron
microscope image
above, bacteriophages
are infecting an E. coli
bacterium.
Confirmation of DNA Function
virus particle
labeled with 35S
virus particle
labeled with 32P
bacterial cell (cutaway view)

Alfred
Hershey and
Martha Chase
(1952) used
radioisotope
tracers on
viruses.

label outside cell
label inside cell
What did
this
prove?
(see the next slide)
Chapter Hershey
10
and Chase’s
Experiments
The Search for DNA’s Structure

Linus Pauling (1951)
discovered the 3-D
structure of proteins, &
the presence of 20
essential amino acids.
 What were the 3D
structures of proteins?
 Following his discovery,
scientists began to believe
that the three-dimensional
structure of DNA could
also be discovered.
3D Model of hemoglobin
The Base Pairing Rule
–In 1949, Erwin Chargaff disclosed 2 important clues
to DNA’s structure: (1) The amount of adenine relative
to guanine differs from one species to the next, (2) the
amount of adenine in a DNA molecule is always equal
to the amount of thymine & the amount of guanine is
always equal to the amount of cytosine!

Base pairing between
the two nucleotide
strands in DNA is
constant for all species
(A with T and C with G).

one base pair
The sequence of bases
is different from
species to species.
DNA - a spiral double helix

Rosalind Franklin (left) - A
crystallographer who
identified the helical shape
of DNA by using x-ray
defraction.
 A picture of a DNA
refraction----------->
–Her work provided the
evidence needed to solve
the mystery of DNA
structure.
Rosalind Franklin’s X-ray of DNA
CAN YOU
SEE THE
X IN THE
MODEL
TO THE
RIGHT??
Can you see the steps of
the twisted ladder (helix)
in the photograph? Why
is the 4th step smeared?
Finally, in 1953,
James Watson &
Francis Crick
(left) solved the
mystery of the
structure of the
DNA molecule.
For this
achievement
they were
awarded the
Nobel Prize.
The Structure of DNA


The DNA molecule is made up of smaller
units known as nucleotides (shown below).
A nucleotide is composed of three parts:
• A five-carbon deoxyribose sugar…
• A phosphate group…
• One of four nitrogen-containing bases:
•
•
•
•
Adenine
Guanine
Cytosine
Thymine

DNA - chains (2 strands)
of nucleotides joined by
hydrogen bonds between
bases.
 A “twisted ladder” shape
known as a “double
helix” is formed.







A. DNA Replication:
Each organism has its
own unique nucleotide
sequence in its DNA.
DNA must be copied
for cell division
( replication).
The sides of the
DNA ladder are
made of sugars &
phosphate groups.
The “rungs” of the
ladder are made of
nitrogenous bases.
DNA Replication
Chapter
10
Comparing
DNA and RNA
DNA Replication

DNA polymerases
attach free nucleotides
to the unzipped
strands.
 DNA ligases seal new
short stretches of
nucleotides into one
continuous strand.
 In which direction is a
DNA molecule built?
 5’ to 3’
DNA Organization in Chromosomes




Each chromosome
consists of one DNA
molecule.
Proteins keep all the
DNA from becoming a
tangled mess.
Histones are like spools
for winding up small
stretches of DNA.
A nucleosome is a DNAprotein spool.