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GENETICS 2:
DNA
STRUCTURE
AND
FUNCTION
1.Explain how DNA was
discovered:
In 1868, Miescher found
DNA in pus cells and fish
sperm, but he didn’t know
what it was.
2.What organisms did Fred
Griffith experiment with?
S – strain of pneumonia causing
bacteria that caused pneumonia
and a R – strain that did not
cause pneumonia.
3. Compare and contrast the
organisms used by Griffith:
.
The S – strain and the R – strain are
the same bacteria except that the s –
strain has a sticky outer capsule to
stick to its host and the R – strain has
no capsule.
4.What is BACTERIAL
TRANSFORMATION?
When one bacteria comes into
contact with another bacteria. It
will take a portion of the other
bacteria’s DNA and gain new traits.
5. Summarize the Fred Griffith experiments that led
to the accidental discovery of bacterial
transformation:
He injected mice with R cells, and the mice lived.
He then injected mice with S cells and the mice
died, live s cells found in the mouse blood.
S – cells were heated, then injected into the mice,
and the mice lived.
Dead S cells and live R cells were injected into the
mice. Mice died. Live S cells found in the
mouse blood.
6. What were the final results of the
Fred Griffith Experiments?
.
Some unknown transformation factor
had changed the harmless R cells into
deadly S cells that caused pneumonia.
7.What new characteristic had
been gained by the bacteria
in the Griffith experiments?
The R cells began to develop a
sticky outer capsule.
.8. What two substances were
suspected of causing the bacterial
transformation ?
PROTEIN and NUCLEIC ACID
.
.
9.Who was the first scientist to
claim that DNA was the one
responsible for the
transformation?
OSWALD AVERY
10. Who were Hershey and Chase?
.
Two scientist who run a series of
experiments with viruses and bacteria
that proved that DNA was the part
responsible for bacterial
transformation.
11.What is a bacteriophage and why was it
chosen for the Hershey and Chase
experiments?
The bacteriophage is a virus that invades
bacteria cells.
The bacteriophage was selected because it is
only made up of a strain of DNA and a
protein coat.
.12. Explain the
Hershey and Chase
experiments: (4)
(a)The outer protein coat of the virus was labeled
with radioactive sulfur.
(b)The nucleic acid was labeled with radioactive
phosphorus.
(c)The radioactively tagged virus was observed
invading a bacteria cell.
(d)It was noticed that the sulfur labeled protein
stayed outside the cell and the phosphorus
tagged nucleic acid went inside and took over the
cell.
13. What did the Hershey and Chase
experiments prove?
.
The Hershey and Chase experiment
proved that it was the nucleic acid
that was the transforming factor.
14.What is a nucleotide?
The sub unit that DNA is made of.
Chains of nucleotides make up a
DNA molecule.
15. Describe a nucleotide (structure)
.
It contains:
(a)A five carbon sugar
(b)A phosphate group
(c)One of four nitrogen bases:
A = Adenine
T = Thymine
G = Guanine
C = Cytosine
16. What makes one nucleotide different
from the others?
T and C are single ringed
pyrimidines and
A and G are double ringed
purines..
.
Double ring structures
Single ringed structures
17.What did Edwin Chargaff observe about
these nucleotides?
(a)All animal species have the same nitrogen
bases in their DNA, but in different
amounts.
(b)In all animal species, “A” always bonded
with “T” and “C” always bonded with “G”.
18
State the techniques used by Rosalind Franklin
in studying DNA and list her discoveries:
Technique: Franklin used X-Ray diffraction to
produce images of DNA..
Discoveries:
(a)DNA exist as a long thin molecule of uniform
diameter.
(b)The DNA structure tends to repeat itself.
(c)DNA is helical.
19.Who were Watson and Crick?
College students who won the
Nobel prize for creating the first
true model of the DNA
molecule.
20.How did Watson and Crick get
the data needed for their model?
They collected data from the work
of earlier scientist.
.21. State the three things that were demonstrated
in the Watson and Crick Model:
(a)“A” always bonds with “T” and “G” always
bonds with “C”.
(b)The backbone (or sides of the ladder) were made
of chains of sugar – phosphate linkages.
(c)The molecule was double stranded and looked
like a twisted ladder.
22.What makes one species
genetically different from other
species?
The sequences of bases are different.
23. Draw, color and label a simple version of the Watson and Crick
Model.
COLOR ALL IDENTICAL SOMPONENTS THE SAME COLOR,
DIFFERENT ITEMS DIFFERENT COLORS.
.24. What holds one side of the
DNA “ladder” to the other side of
the DNA “ladder”?
Hydrogen bonding between the
base pairs.
.25.
Explain DNA replication:
(a)An enzyme called DNA helicase breaks the
hydrogen bonds between the base pairs and
UNZIPS the ladder.
(b)DNA polymerase brings in free floating
nucleotides from the cytoplasm and
attaches them to the exposed bases.
(c)DNA ligase seals the new nucleotides to
the growing strand.
.26. Why is DNA replication
considered “semi-conservative”
replication?
Each replicated chromosome contains
one old side and one new side.
.27.
Do wrong base pairs ever connect
together? If so, what would happen? How is
this prevented?
Yes it happens.
The chromosome would not function
properly.
The replicate is proof read by DNA
polymerase and the incorrect bases are
replaced by the correct ones.
28.What prevents the DNA from tangling up
as it forms human chromosomes?
(a)Histones spool up the DNA into units
called nucleosomes.
(b)Another histone stabilizes the DNA into
loops.
(c)Another histone arranges the loops into
“domains”.
.That’s all until next time.
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