Download Chapter 9. Pg 189 DNA: The Genetic Material

A quick review! AKA: What you
SHOULD know by now.
The structure of
chromosomes: A
chromosome consist of
DNA tightly coiled around
proteins.
What is a gene? A
segment of DNA that
codes for a protein or
RNA molecule.
DNA is copied
during the S
phase of the cell
cycle.
Changes in DNA are called Mutations.
Original DNA strand: ABCDEFG
Types of mutations:
1)Deletion: ABCEFG – a nucleotide is missing
2) Substitution: ABKEFG – a nucleotide is substituted (K for C).
3) Insertion: ABGCDEFG – a nucleotide is inserted (G). All other
nucleotides are present.
4) Translocation: ABCDJEFG – a nucleotide is brought in that is not in
the original strand at all.
5) Replication: ABBCDEFG – a nucleotide is repeated.
And, last but not least- don’t forget Mendel’s Theory of
Heredity:
1) For each inherited character, an individual has 2 copies of the
gene- one from each parent.
2) There are alternative versions of genes.
3) When two different alleles occur together, one of them may be
completely expressed, while the other may have no observable
effect on the organism’s appearance.
4) When gametes are formed, the alleles for each gene in an
individual separate independently of one another.
Chapter 9. Pg 189
DNA: The Genetic Material
Section 1 Key Terms:
QUIZ TOMORROW ON
THESE TERMS.
Vaccine: a substance that is prepared from killed or
weakened disease-causing agents, including certain bacteria.
Virulent: Describes an organism that is able to cause disease.
Transformation: A change in genotype caused when cells
take up foreign genetic material.
Bacteriophage: AKA ‘phage’; it is a virus that infects bacteria.
A Little History
Frederick Griffith was researching a vaccine for pneumonia and
discovered that genes could be changed when cells take up
foreign material. This change in genetic material is called
transformation.
•In order to find a vaccine, he used two strains of bacteria.
•The two strains were called Steptococcus pneumonia or S. pneumoniae.
•One strain was enclosed in a capsule made of polysaccharides that protected it from the
immune system.
•This characteristic, helped make this strain be able to cause pneumonia.
•This ability to cause disease makes an organism virulent.
•This strain was virulent.
•The capsule around strain one strain
causes the bacteria to grow with smooth
edged colonies in a petri-dish.
•This is call the “S bacteria” or Smooth
strain.
•Mice infected with the S bacteria died.
•The second strain did not have a polysaccharide
coat, so it was unable to cause disease.
•In a petri-dish, this bacteria causes round edged
colonies.
•It is referred to as the‘Rough Strain’ or ‘R-strain’.
•Mice infected with the R bacteria did not die.
S. pneumonia
This is what he knew, but he didn’t know why it happened.
•Griffith wanted to know what was causing
the death.
•He knew the only difference between the
two strains was the presence of a capsule on
the S strain.
•So, he injected dead S strain into the mice.
This left only the capsule alive in the mice.
•But, the mice did not die.
____________________________________
•Next, he made a vaccine of weakened S
strain bacteria, by raising their temperature.
• This produced “heat-killed” bacteria.
•Heat killing bacteria allows bacteria to stay
alive, but prevents them from being able to
reproduce.
•The mice still lived.
___________________________________
•This meant that the capsule was not the
cause of death.
•Next, he mixed the harmless R strain
bacteria with the harmless heat killed
bacteria.
•This mixture killed the mice.
•When he examined the dead mice, he
found that the harmless R strain had
acquired capsules and became harmful S
bacteria while in the mice.
•This change is called transformation, but
he didn’t know how it had occurred.
•100 years later, Oswald Avery and his team
discovered that DNA was the source of this
transformation, not proteins.
•His experiments showed
that DNA contained the
instructions of making the
capsule around the
bacteria.
Viral Genes & DNA
•Although Avery had shown that DNA was responsible, many scientists still
believed protein was responsible.
•They knew protein had many important responsibilities in a cell but, they
didn’t know much about DNA.
• 1952: Alfred Hershey & Martha Chase .
•At this time, it was known that viruses were
made of DNA or RNA and were surrounded by
a protective protein coat.
•These are called bacteriaphages or phages.
They are viruses that infect bacterial cells.
Once inside the cell, they
reproduce and create more viruses. The
bacteria cell ruptures and the new viruses
are released.
•Hershey & Chase
concluded that the DNA
of viruses is injected into
the bacterial cells, while
most of the viral proteins
remain outside.
• The injected DNA
molecules causes the
bacterial cells to produce
more viral DNA and
proteins.
Homework: DUE TUESDAY
•Page 193 # 1 and # 6.
NOW
•Section 1 Vocabulary quiz.
Section 1 Bellwork Quiz
Take out one sheet of paper. Match the terms with the correct
definition.
A)
B)
C)
D)
Vaccine
Virulent
Transformation
Bacteriaphage
1) This describes a microorganism or virus that causes disease and that
is highly infectious.
2) A virus that infects a bacteria.
3) A substance prepared from killed or weakened pathogens and
introduced into a body to produce immunity.
4) The transfer of genetic material in the form of DNA fragments from
one cell to another or from one organism to another.
Section 1 Scientist Bellwork
Answer the following questions using the choices below.
Write the correct letter.
1) Who discovered transformation?
2) Who performed the first experiment that correctly
identified the molecule that carries genetic info as DNA
and not proteins?
Choices:
A) Oswald Avery
B) Martha Chase
C) Frederick Griffith
D) Alfred Hershey
Section 2: The structure of DNA
Key Terms:
1. Double Helix
2. Nucleotide
3. Deoxyribose
4. Base-Pairing Rules
5. Complementary Base Pair
Quiz
tomorrow
on these
terms.
Watson and Crick
•Found the model of DNA. This model showed how DNA was able to
serve as the genetic model.
•They discovered:
•
-That a DNA molecule is a double
helix.
•
-That each strand is made up of
linked nucleotides.
•
-Each nucleotide is made up
of three parts:
1) A phosphate group (same for each
nucleotide in a molecule of DNA).
2) A 5-carbon sugar molecule
(deoxyribose- same for each nucleotide
in a molecule).
3) A nitrogen-containing base (may be
adenosine, guanine, thymine, or cytosine).
DNA Nitrogen Bases: There are 2
groups and 4 bases.
Purines are nucleotides that
are bulky and double-ringed.
Pyrimidines are nucleotides
that are small and singleringed.
The nitrogen base in a
nucleotide can be Thymine,
Cytosine, Adenine, or
Guanine.
Pyrimidines
Purines
Base Pairing Rules
• Purines (Adenosine or Guanine) are always paired with pyrimidines (Thymine or
Cytosine).
• An Adenosine base on one strand always pairs with the Thymine base on the
opposite strand with 2 hydrogen bonds.
• A Guanine base on one strand always
pairs with the Cytosine base on the
opposite strand with 3 hydrogen bonds.
• This pairing is due to the structure and
size of the nitrogen bases.
• The hydrogen bonds keep the two
strands of DNA together.
• The strictness of base pairing rules results in
two strands of DNA that contain complementary
base pairs. This means that the sequence of
bases on one strand will determine the
sequence of bases on the other strand.
Who discovered this stuff?
Chargaff: 1948, Erwin Chargaff discovered
that for each organism he studies, the
amount of adenine always equaled the
amount of thymine and that the amount
of guanine always equaled the amount of
cytosine. Now, we know why.
Wilkins and Franklin: Developed high X-ray
diffraction photographs of strands of DNA.
These photos suggested that DNA
resembled a tightly coiled helix and was
composed of three chains of nucleotides.
Watson and Crick: They took this info and
their knowledge of chemical bonding and
determined the structure of DNA.
Homework
Study Section 2 terms and end of section questions
(pg 197 #1,4,5,6). Be ready for a Bellwork Quiz on
vocabulary.
Section 2 Vocab Quiz
Take out one sheet of paper. Number your paper 1-5. Match the terms
(the correct letter) with the correct definition.
1. Double helix
2. Nucleotide
3. Deoxyribose
4. Base-Pairing Rules
5. Complementary Base Pairing
a. The rules stating that cytosine pairs with guanine and adenine pairs
with thymine in DNA, and that adenine pairs with Uracil in RNA.
b. In a nucleic-acid chain, a subunit that consists of a sugar, a phosphate,
and a nitrogenous base.
c. A characteristic of nucleic acids in which the sequence of bases on
one strand is paired to the sequence of bases on the other.
d. The spiral staircase structure characteristic of the DNA molecule.
e. A five-carbon sugar that is a component of DNA nucleotides.
Sec 3: The Replication of DNA
DNA Replication: the process of making a
copy of DNA.
Steps of DNA Replication:
1) An enzyme called DNA helicase breaks
the hydrogen bonds that link the two DNA
strands together. The double helix unwinds
and the two original DNA strands separate. Once the two strands
are separated, additional proteins attach to each strand in order to
hold them apart and keep them from wrapping back together. The
areas where the strands are held apart are called replication forks.
2) At the replication fork, DNA polymerases add complementary
nucleotides to each strand, according to the base pairing rules.
3) Two DNA molecules form that are identical to the original DNA
molecule.
1) DNA helicases
separate the two
original DNA
strands.
2) DNA polymerases
add
complementary
nucleotides to
each strand.
3) Two DNA
molecules form
that are identical
to the original
DNA molecule.
Checking For Errors
• If an error occurs and the wrong nucleotide is added to the
strand, this is corrected with DNA polymerases.
• As DNA polymerases are adding nucleotides, they can only
move on to the next one if the previous one is correctly
paired to its complementary base. If there is a mismatch,
then the DNA polymerases can move backwards and make
the correction.
• This “proofreading” reduces errors in DNA replication to
about one error per 1 billion nucleotides.
The Rate of Replication
•In prokaryotes, DNA molecules are circular. So, there are two
replication forks that form at a single point and replicate DNA by moving
away from each other until they meet on the other side of the DNA
circle.
• If eukaryotes
(humans) were
done in this same
way, it could take 33
days to replicate a
strand of DNA.
•Each human chromosome is replicated in about 100
sections that are 100,000 nucleotides long, each section
have its own starting point.
•Since this means that multiple replication forks are
working at the same time, an entire human chromosome
can be replicated in 8 hours.
This process
occurs at
multiple places
throughout the
strand of DNA,
until replication
is complete.