Download 7 DNA

DNA
Reading Assignment:
• Read pages 287-290 and prepare to
discuss.
• If you complete that before we are
ready to discuss, please read through
the rest of the section, page 294.
Questions:
• What organelle is known as the “control center” of
the cell?
▫ Nucleus
• What structures are found in the nucleus?
▫ Chromosomes (Chromatin, DNA)
• What are located on chromosomes?
▫ Genes
• What are chromosomes composed of?
▫ DNA (wound around proteins)
• How do genes and chromosomes control the activity
of a cell?
▫ By producing proteins that regulate the cellular
functions or become part of the cell structure.
Vocabulary
• Transformation
• Bacteriophage
• Nucleotide
• Base pairing
What was Griffith trying to do?
• Trying to learn whether or not a toxin produced
by the bacteria was the cause of pneumonia.
• What are some questions he could ask?
Look at figure 12-2, page 288
• What was Griffith trying to learn when he set up this
experiment?
▫ How bacteria caused pneumonia
• How did Griffith show that the disease-causing
bacteria were killed by the heat?
▫ He tried to grow them in a petri dish. If the bacteria
didn’t grow, then he knew he had killed it.
• What result was Griffith expecting when he
injected the mixture of live harmless bacteria and
the heat-killed disease-causing bacteria?
▫ The mouse to live.
Immunizations
• How many of you remember getting
immunizations?
• How do immunizations work?
▫ Immunizations are toxoids or inactivated toxins
from the toxins that are produced by the bacteria
that make us sick.
• Why do you think it’s important to learn how
bacteria cause disease?
▫ To find a cure for the disease, or a means to
prevent it.
• This was what Griffith was doing!
• He was showing how a toxin that is produced by
the bacteria causes pneumonia.
• Then Avery expanded upon his work… He
wanted to know what was most important for
this transformation to occur.
▫ He isolated items and destroyed them, till he
found the one item, that when destroyed ….
Transformation no longer occurred.
▫ What was that item?
 DNA
Hershey-Chase Experiment
• A Bacteriophage is a virus
that infects and kills a
bacteria.
Hershey-Chase Experiment
How did they get the parts of the
Bacteriophage radioactive?
• They soaked the bacteriophages in the
radioactive isotopes – Because DNA has
Phosphorus already, it incorporated the
radioactive Phosphorus.
• They did the same with another set of
bacteriophages with ulfur, and because the
protein coat already contains sulfur, it
incorporated the radioactive sulfur.
DNA History
• Griffith –
▫ Experiment: Using mice, he observed
transformation – Live harmless bacteria
transformed into disease causing bacteria.
▫ Live, Disease Causing Bacteria
▫ Live, Harmless Bacteria
▫ Dead (Heat Killed) Disease Causing Bacteria
▫ Dead (Heat Killed) Disease Causing Bacteria
mixed with Live Harmless Bacteria
Griffith Experiment
(Pneumonia)
More DNA History
• Avery–
• Experiment: Concluded that the genetic
material in bacteria was DNA not proteins
▫ Repeated Griffith’s experiments with enzymes
•
•
•
•
•
Destroy proteins
Destroy lipids
Destroy carbohydrates
Destroy RNA
Destroy DNA
• Hershey - Chase–
▫ Experiment: Used Bacteriophages to show that
DNA is what stores and transmits the genetic
information from one generation to the next.
▫ P32 (Phosphorus 32)
 Radioactive marker attached to DNA inside of
Bacteriophage
▫ S35 (Sulfur 35)
 Radioactive marker attached to protein coat of
Bacteriophage
The Discovery of DNA
• Rosalind Franklin – made x-ray of DNA
• J. Watson & F. Crick – made the 1st model of the
structure of DNA! (using R. Franklin’s x-ray)
Watson & Crick
DNA
Watson & Crick –
created the double helix model for DNA.
Structure of DNA
• DNA is a long molecule made up of units called
nucleotides.
• Each nucleotide is made up of three parts:
▫ a 5-carbon sugar called deoxyribose,
▫ a phosphate group, and
▫ a nitrogenous base (Nitrogen Containing).
• The backbone of DNA: sugar and phosphate
groups
• The nitrogenous base stick out from the sides
and can be joined together in any order,
meaning that any sequence of bases is possible.
Nitrogenous Bases
• There are four kinds of nitrogenous bases.
• They are divided into two classes: purines and
pyrmidines
▫ Purines – Adenine and Guanine
▫ Pyrimidines – Cytosine and Thymine
Structure of DNA
Shape = Double Helix
Made up of nucleotides:
deoxyribose, phosphate group, and a
nitrogenous base (A, T, C, or G)
Chargaff’s Rules
• Chargaff discovered
how the nitrogenous
bases bond together.
• He discovered that
Adenine always
bonds with Thymine
and that Cytosine
always bonds with
Guanine.
Double
Ring
Single
Ring
The Nucleotides
Phosphate – sugar
“backbone”
The sugars also attach to
the bases.
Bases attach to each
other by a weak
hydrogen bond.
The 2 strands are
“complementary” to
each other. (base pair
rule!!!)
What is the base pair rule?
Adenine (purine)
connects to Thymine
(pyrimidine)
A-T
Guanine(purine)
connects to Cytosine
(pyrimidine)
G-C
Prokaryotes & DNA
• In prokaryotes,
DNA molecules are
located in the
cytoplasm of the
cell.
• Most prokaryotic
DNA is a single
circular molecule
that contains nearly
all the cell’s genetic
information.
Eukaryotes & DNA
• Many eukaryotes
have 1000 times as
much DNA as
prokaryotes.
• DNA is located in the
nucleus in the form of
chromosomes.
• Chromosomes are
DNA wound tightly
around proteins
called histones.
DNA Length
• E. Coli have about 4,639,221 base pairs. It is
about 1.6mm in length. This sounds small until
you realize the bacteria is only 1.6µm in
diameter.
• Thus DNA must be wrapped tightly to fit
into cells. Imagine fitting 900 yards (300m) of
rope into a backpack.
DNA replication……
• Occurs during S
phase of
Interphase during
the cell cycle.
• Makes an exact
copy of all DNA.
DNA replication……
• Is “semiconservative” – 1
strand is “old” & the
other strand is “new”.
DNA Replication
• The DNA molecule separates
into two strands
• Then produces two new
complimentary strands
following the rules of base
pairing (Chargaff Rules).
• Each strand of double helix of
DNA serves as a template, or
model, for the new strand.
How It Occurs
• DNA replication is carried out
by a series of enzymes.
• The enzymes unzip the DNA
molecule creating two strands
that serve as templates.
• Complimentary bases are
added to the strands
▫ Example: ATTCGAG
.
TAAGCTC.
What is needed for
replication?
• Replication requires
enzymes:
1) Helicase – unwinds
.
DNA
2) DNA polymerase
.
– puts new nucleotides
.
in place & proofreads
Replication Review
• Each new DNA molecule has one new strand
and one strand from the original molecule.
▫ What is this called?
▫ Semi-conservative
• The enzyme DNA polymerase, the principal
enzyme, “proofreads” the new DNA strands,
helping to maximize the odds that each molecule
is a perfect copy of the original.
▫ This is what I call: “The Police”
The process of DNA replication
1)
DNA unwinds &
unzips – uses
Helicase
2) Replication fork forms
(area where 2 strands
separate)
* there are
several replication
forks at the same
time.
3) DNA polymerase
adds new nucleotides
to each DNA strand,
following the base pair
rule!