12-1: DNA
Biology 2
Introduction
• In the mid 1900’s biologists
wondered:
• How do genes work?
• What are they made of?
• How do they determine
characteristics?
• Are they single molecules?
Introduction
• Biologists needed to discover
the chemical nature of genes
• If they could figure out how
genes carried genetic
information, could understand
how genes control
characteristics of living things
Griffith
and
Transformation
• 1928: Frederick Griffith was trying
to figure out what type of
pneumonia made people sick
• Found 2 different types: smooth
and rough
– Smooth was deadly; Rough was
not
• Gave mice shots with different
types
– Smooth (alone) killed mice
– Rough (alone) did not kill mice
– Smooth and Rough together killed
mice
Griffith
and
Transformation
• Figured out that rough was
transformed into smooth when
together
• TRANSFORMATION: process in
which one strain of bacteria is
changed by a gene or genes
from another strain of bacteria
• Griffith discovered that the
ability to cause disease was
inherited by a gene
Avery
and DNA
• 1944: Oswald Avery wanted to
repeat Griffith’s experiment
• Created a “juice” from heatkilled bacteria
• Used enzyme that would
destroy DNA
• Transformation did not
happen!
• Avery discovered that DNA
stores/transmits genetic info
HerseyChase
Experiment
• 1952: Alfred Hersey and Martha
Chase were interested in which
part of a virus could infect cells
• Used bacteriophages for
experiment to study infection
• BACTERIOPHAGE: virus that
infects bacteria
• Used radioactive markers on
outside protein coat and DNA
• Discovered genetic material of
bateriophage was DNA (not
outside protein coat)
Components
and
Structure of
DNA
• DNA had to be able to:
1. Genes had to carry
information to next
generation
2. Had to determine
characteristics that can be
inherited
3. Be easy to copy each time cell
divides
Components
and
Structure of
DNA
• DNA is made of building blocks
called nucleotides
• NUCLEOTIDES: monomer of
nucleic acids made up of a 5carbon sugar, a phosphate
group, and a nitrogenous base
• Can have 4 different types of
base:
– Adenine
– Guanine
– Thymine
– Cytosine
Components
and
Structure of
DNA
• Backbone of DNA is sugar and
phosphate groups
• FORM THE OUTSIDE OF THE
“LADDER”
• Bases bond together to
connect inside
• FORM THE INSIDE (STEPS) OF
THE LADDER
PHOSPHATE
SUGAR
BASE
Components
and
Structure of
DNA
• Shape of DNA is called “Double
Helix”
– Looks like a twisted ladder!
• Discovered by Francis Crick and
James Watson in 1953
• Chargaff’s Rule says that base
pairs will always have equal
numbers
– Adenine = Thymine
– Cytosine = Guanine
Section Assessment
1. ___________: process in which one strain
of bacteria is changed by a gene or genes
from another strain of bacteria
2. DNA can have 4 different types of bases:
___________, ___________, ___________,
___________
3. Shape of DNA is called “___________”
4. Chargaff’s Rule says that ___________ will
always have ___________