Download DNA as Genetic Material

DNA as Genetic Material
DNA vs. Protein
At first protein was
thought to be genetic
material
- 20 possible AAs in
Protein, 4 nucleotides in
DNA
Griffith’s experiment
- Fredrick Griffith found that
nonpathogenic bacteria
could be made pathogenic
by incubating with heatkilled pathogenic bacteria
- bacteria were
“transformed”
Avery-MacLeod-McCarty
experiment
identify transforming substance in
Griffith’s experiment
- Isolated DNA, RNA, and Protein
from heat-killed pathogenic
bacteria
- tested which would transform
live nonpathogenic bacteria
- transformation occurred w/DNA
only
Hershey-Chase experiment
(blender experiment)
Used T2 bacteriophage (virus that
infects bacteria) to determine if
protein or DNA is genetic material
- DNA contains P and not S
- protein contains S and not P
- radioactive S and P were used to
label protein and DNA
- radioactive P was found in E. coli
not S when bacteriophage
infected
Opener 12-12-16
Explain how in the Hershey-Chase experiment
they were able to determine if it were DNA or
protein that is transferred from bacteriophages
to bacteria during infection.
3-D structure of DNA
Erwin Chargaff identified
that amount of A and T is
Equal, and amount of G
and C is equal (Chargaff’s
Rule)
Rosalind Franklin X-ray
crystallography
Rosalind Franklin made X
ray images of DNA crystals
- saw distinct diffraction
pattern
- James Watson determined
that the diffraction pattern
was of a helical molecule
made of 2 strands
James Watson and Francis
Crick
- Worked out DNA base
pairing, explains
Chargaff’s rule
- Determined that DNA
strands are antiparallel
- finalized 3-d structure
DNA replication
Process that occurs in S
Interphase
Semiconservative nature of
replication
- Replication begins with 1 double
stranded DNA and makes 2
double-stranded daughter DNA
molecules
- each daughter DNA contains 1
of original parent DNA strands
Replication process
DNA unwinding (helicase)
Priming (primase)
Synthesis (DNA polymerase)
Process begins at origins
of replication (OOR)
Unwinding DNA
Helicase enzyme breaks
hydrogen bond between
base pairs
Opens up DNA for
replication enzymes to
have access
Priming
DNA polymerase cannot
initiate synthesis with
DNA nucleotides
-RNA primer is used to get
DNA polymerase started
-Primase adds a few RNA
nucleotides, base paired
to the parent strand
Synthesis
DNA polymerase matches
nucleotides to the
template strand by base
pair rules
- Adds nucleotides to 3’ end
of primer
- catalyzes reaction that
links nucleotides together
along the backbone of new
DNA strand
Leading and lagging
strands
DNA polymerase can only add
nucleotides to 3’ end of
growing strand
For each daughter DNA being
synthesized there is leading
strand and a lagging strand
Leading strand grows from
OOR in 3’ direction
Lagging strand is filled in
discontinuously on the 5’ end
of the strand
Lagging strand synthesis
Numerous RNA primers
used to initiate fragments
(called Okazaki fragments)
DNA polymerase I
replaces RNA primer with
DNA nucleotides
Ligase used to link
backbone of fragments
Telomeres
Eukaryotic chromosomes
are linear, they have an ending
Telomeres are special sequences
at the end of chromosomes
Each replication event results in a
shortening of Telomeres
In gametes cells telomerase
enzyme lengthens the telomeres