Biol 121- 2010.01.22- Genetics- DNA, Cell Cycle (Ch. 14, Ch. 11).docx

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Biol 121 225
Freeman 295-302, 222-7 Jan 21, 10
DNA Ch. 14
Strain and virulence -a strain is a population of genetically
identical individuals
-strains that affect humans vary in their
virulence – their ability to cause disease
and death
-virulent strains cause disease, avirulent
(benign) strains do not
Medium -a liquid or solid that is suitable for
growing cells (a petri dish can contain
nutrient-containing medium)
Griffith and transformation
-Results and Conclusion
-Griffith in the 1920s did experiments to
develop vaccine against Streptococcus
pneumoniae bacterium
-Griffith worked with strains identifiable by
eye when grown on a nutrient-containing
medium in a petri dish
-on a solid medium, cells from the
nonvirulent strain form colonies that look
rough (R) ; cells from the virulent strain
form colonies that look smooth (S)
-Griffith injected mice with R strain, S
strain, heat-killed S strain, and R strain
with heat-killed S strain
-found that mice died when injected with S
strain, and with R strain with heat-killed S
strain; mice did not die with R strain nor
heat-killed S strain
-Griffith proposed that something from the
heat-killed S cells “transformed” the
nonvirulent R cells
Culture -a collection of cells that grows under
controlled conditions – usually suspended
in a liquid medium or on the surface of a
solid growth medium
Hersey-Chase experiment – were genes
made of protein or DNA?
-Background info
-study how a virus called T2 infects
Escherichia coli
-T2 infections begin when viruses attached
to cell wall of E. Coli and injects genes
-genes then direct the production of a new
generation of virus particles inside the
infected cell, which acts as a host for the
DNA Ch. 14
Two important facts of their strategy
Experimental setup
parasitic virus
-during infection, protein coat of original
parent virus left behind
-proteins present in T2 contain sulphur but
not phosphorus; DNA contains phosphorus
but not sulphur
-grow viruses in presence of P-32 which
will then have viral DNA, and some viruses
in presence of S-35 which will then have
viral protein
-allow viruses with labelled DNA to infect
one culture of E. Coli cells and viruses with
labelled protein to infect another
-agitate cultures in kitchen blender to
separate empty viral protein coats from
bacterial cells in each culture
-centrifuge solutions of bacterial cells from
each culture to force cells into a pellet,
record location of radioactive labels
-DNA hypothesis: radioactive DNA located
within pellet
-protein hypothesis: radioactive protein
will be located within pellet
-radioactive DNA is in pellet, radioactive
protein is in solution
DNA – polymer/monomer? -DNA is a long, linear polymer made up of
monomers called deoxyribonucleotides
-Components of the monomer of DNA,
-deoxyribonucleotides consist of a
deoxyribose (sugar) mcule, a phosphate
group, and a nitrogenous base
-deoxyribonucleotides link together into a
polymer when a phosphodiester bond
forms between a hydroxyl group on the 3’
carbon of deoxyribose and the phosphate
group attached to the 5’ carbon of
Double helix and its formation -two individual DNA single strands will run
alongside in opposite direction –
Biol 121 225
Freeman 295-302, 222-7 Jan 21, 10
DNA Ch. 14
antiparallel fashion
-the antiparallel strands will twist around
each other into a spiral or helix because
certain of the nitrogen-containing base fit
together in pairs inside the spiral and form
hydrogen bonds
Interactions in the double helix -the reason for the double helix are the
hydrogen bonds between bases as well as
stacking interactions (van der Waals forces
or hydrophobic interactions)
-complementary base pairing discusses
the specific pairing rules for hydrogen
bonding of nitrogen-containing bases (A to
T, C to G)
DNA is semiconservative (DNA replication) -the three main theories of DNA replication
were conservative, semiconservative and
dispersive models
-semiconservative means that each newly
made DNA mcule comprises one old strand
and one new strand
DNA synthesis direction (replication) -DNA monomers (deoxyribonucleotide
triphosphate - dNTP) are added to the 3’
end of the strand and a phosphodiester
bond is formed
(5 3’)
The Cell Cycle Ch. 11
Cell theory -all organisms are made of cells and cells
arise from pre-existing cells
-how do new cells arise from pre-existing
-cell division
Chromosomes are the carriers... -are the carriers of hereditary material –
the instructions for building and operating
the cell
Two types of nuclei division
Types of cells
-leads to production of sperm and eggs;
the other type of nuclear division leads to
production of all other cell types
-sperm and eggs = male and female
reproductive cells called gametes