Download Biology CP- Ch. 11 DNA- 11.1

DNA –The Language Of
Life
Chapter 11
11.1 What is the chemical
in genes?
• Computer keyboard analogy.
– > 100 keys ; correct order.
• Students in the classroom.
– Same parts-arms,legs, eyes etc.
– All people have the same chemicals.
– It’s the combination of chemicals that
produces the many different
characteristics.
• Just as letters form sentences,
chemicals form DNA.
DNA is the chemical of genes
• In the cell cycleDNA replicates
DNA divides in mitosis/meiosis.
• Each cell has genetic
blueprint instructions.
The story of how we learned
DNA was the genetic material:
• Experiments- Griffith- Transforming
Factor.
– Pneumonia- caused by Streptococcus
pneumoniae.
– 2 Strains of bacteria.
• Smooth strain- capsule.
– Caused pneumonia in mice.
• Rough strain - no capsule.
– Did not cause pneumonia in mice.
– Heat killed smooth strain.
• Did not cause pneumonia in mice.
– Combined heat-killed smooth strain and
rough strain bacteria.
• Caused disease in mice .
Griffith’s Experiment
•
Figure 11-1 Griffith showed that although a deadly strain of bacteria could be
made harmless by heating it, some factor in that strain is still able to change other
harmless bacteria into deadly ones. He called this the "transforming factor."
What happened?
• Griffith examined the blood of
the dead mice and found
smooth strains of bacteria.
• The Rough strain was
transformed to become smooth.
• All descendents of the
transformed bacteria were also
smooth and caused disease.
• Griffith called the substance
“transforming factor”.
Experiments to identify the
“transforming factor”
• Scientists knew chromosomes
were involved in inheritance.
• Chromosomes are made up of
proteins and DNA.
• Most scientists thought the
hereditary material was in
protein rather than DNA.
Avery’s Experiment
• Avery used enzymes.
• After protein destroying enzymes
were used on Griffith’s heat treated
and live rough mixture.
– rough bacteria were transformed
showing that protein was not the
transforming factor.
• Then DNA destroying enzymes were
used.
– rough bacteria were not transformed.
• DNA was the transforming factor.
Hershey and Chase Bacteriophage
Experiment
•
Hershey & Chase’s Bacteriophage
Experiment
Proves DNA is the genetic material
• Viruses are not cells.
– nucleic acid wrapped in a protein coat.
– only reproduce by infecting a living cell.
– viral genetic material directs host cell to
make more virus copies.
• Bacteriophage -viruses that attack
bacteria.
• Bacteriophage of Hershey &Chase.
– outer coat of protein; inner core of DNA.
• Radioactive isotope of sulfur labels
phage protein coat only.
• Radioactive isotope of phosphorous
labels phage DNA only.
• When only phage protein coats were
labeled, radioactivity was detected
outside of the cell.
• When phage DNA was labeled
radioactivity was detected inside the
cell.
• Conclusion : phage DNA enters the
bacterial cell , NOT protein.
• DNA is the genetic material !
11.2 Structure of DNA
pp 229-231
Nucleic Acids• Function - store and transmit genetic
information.
• Nucleic Acids- made up of many
units of nucleotides(monomers)
• Nucleotides are the building blocks.
• DNA- Deoxyribonucleic Acid
– 4 different nucleotides.
•
•
•
•
A=adenine
G=guanine
C=cytosine
T=thymine
NUCLEOTIDE STRUCTURE
3 PARTS OF A NUCLEOTIDE:
1. Deoxyribose - 5 Carbon sugar
2. Phosphate GroupPhosphorous atom with 4
atoms of oxygen
3. Nitrogenous base.
• Single or double stranded
rings of carbon and
nitrogen
The 4 nucleotides of DNA:
• The nitrogenous base is the difference.
Pyrimidines- single-ring structures.
• Thymine- T.
• Cytosine- C.
Purines- double-ring structures.
• Adenine- A.
• Guanine- G.
• The letters T,C,A,G are used to represent
the bases and also the nucleotides that
contain them.
Sugar-phosphate DNA backbone
Double helix (ladder )model
• Outside of the ladder
– Repeating pattern
– Sugar of one nucleotide is
connected to the phosphate group
of the next.
• Attached nitrogenous bases are
on the inside (rungs)of the
double helix model.
• Nucleotide chains can vary in length.
• Nucleotides can combine in many
different sequences represented by
the letter symbols.
– CTAGCCTTGAC
Nitrogenous Base Pairing:
A=T ( by 2 hydrogen bonds)
G=C (by 3 hydrogen bonds)
Called Complimentary Base Pairing.
Base-pairing rule- each base must pair up
with its complementary base.
Double Helix Structure
• 1950s- Franklin- X-ray
crystallography.
– Showed basic shape to be a helix
• 1953- Watson and Crick model
– Used Franklin’s photos
– Twisting shape-double helix ; 2
nucleotides twist around each other.
– Sugar-phosphate backbone on outside
– Nitrogenous bases on the inside joined
by hydrogen bonds.
process of copying a DNA
molecule.
• The cell uses a “negative” as a copy
to make more DNA.
• Template mechanism.
– 2 strands of the double helix separate.
– A series of enzymes are involved.
– The enzymes “unzip” the molecule of
DNA, breaking the hydrogen bonds
between the base pairs.
– Each strand acts as a negative template
for a new, complementary strand to
form.
– Base-pairing rules are followed.
DNA Replication Continued
• DNA polymerases- the principal
enyme
– enzymes that make the bonds between
the nucleotides of the new DNA strand.
– They also “proof-read” each new DNA.
• DNA replication begins at specific
sites called points of origin.
• Replication proceeds in outward
directions from the points of origin
resulting in replicating bubbles.
• The parent DNA strands open up as
new daughter strands grow.
Result of DNA
replication:
• Result- 2 double stranded DNA
molecules; each one has an old
and complementary new strand.
• DNA replication occurs before a
cell divides.