C & C P. 229
1. Explain why neither cyclins nor kinases alone can cause a
cell to progress through the cell cycle.
Interaction of cyclins and kinases is required for regulation
2. How do controls on the cell cycle protect multicellular
organisms from accumulating large numbers of damaged or
defective cells?
The cycle can be paused (cell-cycle arrest) so that damaged DNA
can be repaired.
3. What is the difference between a cancerous tumor and
metastasis
Metastasis involves the breaking off and movement of cells from
the primary tumor to another location in the organism.
4. What are the functions of tumor-suppressor genes and
proto-oncogenes in noncancerous cells?
They serve key roles in regulating many cellular processes,
including cell division, where proto-oncogenes promote cell
division and tumor-suppressor genes inhibit cell division.
DNA: The genetic material
A few questions to ponder
today:
• What is DNA?
• How did we figure out the
structure of this
important biomolecule?
• How is it replicated for
the cell cycle?
• Steps to the discovery of DNA:
– 1869- Freidrich Miesher
• purified DNA from pus cells obtained from discarded surgical
bandages
– 1923- Robert Feulgen
• developed a procedure that stained this material in the
nucleus
• This enabled him to measure the amount of “stuff” in the
nucleus
• He concluded that virtually every cell nucleus in any plant or
animal has the same amount of this “stuff”
What
was this
in the
Was
it DNA
or a“stuff”
proteinfound
that carried
nucleus
and did it instructions
have anything
to do
the hereditary
from
with
why offspring
look like their
generation
to generation?
Early scientists sawparents?
the structure of the DNA
molecule as too simple to possibly contain the
complex genetic information of an organism
• 1828- Fred Griffith was working on a project that enabled others to point out
that DNA was the molecule of inheritance.
• He was trying to prepare a vaccine against a pneumonia-causing bacterium.
•He discovered that harmless bacteria could turn virulent
when mixed with bacteria that caused disease.
•In other words, he discovered what was called
transformation
a change in phenotype caused when bacteria cells take up
foreign genetic material.
animation
• 1944- Oswald Avery
– continued with Griffith’s experiment to see what the inheritance molecule
was.
– In his experiment he destroyed the lipids, ribonucleic acids, carbohydrates,
and proteins of the virulent pneumonia.
– Transformation still occurred after this. Next he destroyed the
deoxyribonucleic acid. Transformation did not occur. Avery had found the
inheritance molecule, DNA!
• 1952- Alfred Hershey and Martha Chase settled the controversy.
– DNA is the molecule that store genetic info in living cells
animation
• 1951- Roseland Franklin fired x-rays through DNA
crystals, trying to learn how the atoms of the DNA
molecule were arranged
• 1953- James Watson and Francis Crick were shown
Franklin’s photo and immediately determined the
double helical structure of DNA.
Deoxyribonucleic Acid
Phosphate
molecule
Sugar molecule
Nitrogen Base molecule
Hydrogen bonds
Guanine
Adenine
Cytosine
Thymine
DNA Structure
Nucleotides are the subunits:
– a phosphate group
– a 5-carbon sugar molecule
• Deoxyribose
• 5’ end
• 3’ end
– a nitrogen –containing base
• Purines- made up of 2 rings of
carbon and nitrogen atoms
– Adenine (A)
– Guanine (G)
• Pyrimadines- made up of a single
ring of carbon and nitrogen atoms
– Thyamine (T)
– Cytosine (C)
Chargaff’s Rule- (1947)Erwin Chargaff, a chemist who worded at Columbia
found that:
– for each organism studied, the amount of adenine
always equaled the amount of thymine
– and cytosine always equaled guanine.
– This became known as the Base-Pairing Rules
Why does this complementarity exist?
□ The two chains of nucleotides are held
together by 2 or 3 weak hydrogen bonds
that form between the nitrogenous bases:
– Cytosine and guanine have three
hydrogen bonds
– Thymine and adenine have two
hydrogen bonds
□ Each rung of the DNA ladder needs to
have a total of three rings
• Also, One of the strands of DNA runs in
the 3’ to 5’ direction and the other runs
in the 5’ to 3’ direction.
antiparallel
• This is called _______________
DNA cont.
• DNA is the molecular
“blueprint”—
– This “instruction manual”
makes up an organisms genes.
– Encoded in the precise order of
its nucleotides
– The genetic alphabet only
contains 4 letters (ACTG).
– Human DNA contains more
than 3 billion base pairs!
COMPARING PROKARYOTIC AND
EUKARYOTIC DNA:
PROKARYOTES
EUKARYOTES
Configuration of DNA
Circular
linear
Length
1000 micrometers
No
1.8 meters
Yes
Associated proteins
Transient proteins
Histones
# of Chromosomes per
Cell
1
2- 1,262
DNA housed in nucleus?
HOW DO ALL THESE BASE PAIRS FIT IN
THE NUCLEUS?
– a NUCLEOSOME consists of 2 loops of DNA wrapped
around a central cluster of 8 histone molecules.
– This shortens the length of DNA by 1/6.
– This is shortened even further by its coiling into
thicker fibers
• Complete the Concept Map in your packet
• Begin “Journey into DNA”
• Finish crossword puzzle and any of the above
for homework