Download 10/14/04 8:25 am

10/14/04 8:25 am
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What is the Genetic Stuff?
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2 candidates
Proteins
amino acids linked into polypeptide chains with fold and form
into proteins
20 different amino acids used in all living things
amino acids linked by condensation reaction, aka dehydration
synthesis reaction.
DNA
• nucleotides linked together by condensation reaction.
• T,A, C, G bases possible
By 1928 we knew
• "genes" were on chormosomes
• chromosomes had been analyzed and found to contain both
protein and DNA
Why would protein be the "logical" first chocie of hinking
scientists? because of hte man y possibility.
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1941- Beadle and Tatum: " one gene codes for one
polypeptide" hypothesis. Polypeptide- chain of amino acids,
the fundamental building blocks of proteins.
1944- Avery, Colin McLeod, McCarty team, proved that
dna is the genetic stuff.
1950- Chargraff's Rules
• T=A
• C=G
1952- Hershey and Chase- second team to prove that dna is
the genetic stuff.
1953- Watson, Crick, Wilkins and Franklin- determined
that dna is a double helix. Wrote a 1 page paper. Published
in NATURE. Won the Nobel Prize 1962 (except for
Franklin- she died).
1958- Meselson and Stahl- proved that DNA replicates semi
conservatively.
1966- Nirenberg and Khorana: break the genetic language
code.
10/15/04 9:31 am
mendilian genetics: looks at traits, phenotypes
molecular genetics: looks at t's, a's, c's and g's
Major Expieriment #1, Griffith's TGransformation 1928
Genetic Stuff Must Be:
• able to carry mucho information to code for a whole
organism
• able to ontainthe information for making a copy of itself
accurately. Each cell division needs a new accurate copy.
• chemically stabe or ti would not carry info accurately from
one generatio nto the next.
• just "unstable" enough that periodically a mutation can
occur or there would be no variety in life.
Timeline
• 1865- Mendel- traits are passed as distince alleles (various
forms fo the same trait)
• ex: trait= eye color
• alleles= blue, green, hazel, brown
• Mendel studdied patterns of train inheritance- nothing
about the mechanisms and chemicals invovled. Not
many people read his paper.
• 1869- Friedrich Miescher discovered deoxyribonucleic
acid. naming nuclein --> nuclei acid-=> deoxyribonucleic
acid.
• 1900- deVries, Correns, Tschermak independently
rediscover Mendel's work.
• what a coincidence! none of them have heard of
Mendel before. all three wrote their papers within
three weeks of each other. all of them turned them in
to nature magazine to be published at the same time
• 1908- Hardy and Weinberg- laws of population genetics
determined a math formula that explains how recessive
traits stay constant in a stable population.
• fathers of population genetics.
• 1910- Morgan- "genes" are on chromosomes. thread
things had been seen in cells doing the mitosis thing.
Morgan determined that they contained the trait passing
capcity. coined the term "gene"
• 1928- Griffith- first transformation experiments DNA
could be the genetic stuff.
transformation= alter the genes of an organims by incorporating
DNA from an outside source.
Streptococcus pneumoniae= common bacteria knonw to cause
pneumonia. always capitalize genus, not species
• virulent- capable of causing disease.
• Comes in two flavors
• "S"
• smooth
• virulent
• pollysaccharide slime coat covers its recognition
glycoproteins; cannot be detected by host's immune
system.
• "R"
• rough
• non virulent
• no polysaccahraide coat- deletion mutation- detected
by immune system and destroyed before it takes
over. otherwise identical to the smooth form. it is
just missing a gene.
The Experiment:
• S alive -> mouse-> mouse dies
• R alive --> mouse -> mouse lives
• S heat killed -> mouse -> mouse lives
• S heat killed + R alive --> mouse --> mouse dies why??
• dna stays stable up to 80iss degrees celcius
• The R that was alive was transformed into getting the gene
that the s had.
Did "R" form develoop the means to make a slime coat?
Griffith decided a transforming factor was passed form teh dead
"S" to the living "R" backteria and this stuff let them encapusulate
themselves witha polysaccharide slime coat.
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all that meas is that somethign made a change (transform)
and they don't know what it is (factor).
Since there wer ewhole bunches of bacteria all makign slime
coats in the corpe's body, this ability to make slime coats had
obviously been able to passed on to each generation of
bactertia. This transforming facotr was the genetic stuff.
Major Experiment #2- Oswald Avery, Colin, McLeod, and
Maclyn McCarthy's DNA proff- 1944
Repeated Griffiths experiment- isolated the Transformation
Factor (TF)
1. Treatment TF with Proteaste (enzyme which destroys
proteins)--> mouse . Still transformed R-->S: mouse died
10/19/04 8:01 am
2. Treated T.F. with Robonuclease -RNase (enzyme
which destroys RNA) --> mouse. Still transformed R-->S:
mouse died.
3. Treated T.F. with DNase --> mouse. no longer
transformed R-->S: mouse lived!
Purified the TF and did more analysis of the stuff.
Characteristics of Transforming Factor
• Centrifugation- moved rapidly tot he bottom of the tube
suggesting an extremely high molecular weight.
• DNA has an extremely high molecular weight. what
they tsted acted just like dna in a centrofuge.
• Electrophoresis: TF placed in an electric field and it
moved rapidly. Caries a large ionic charge.
• DNA carries a large ionic charge.
• ho electrophoresis works: you ahve a well that you
put your samples in and then immerse them. You then
have a cathode and an anode (opposite charges fron
likewise named ions. The dna hten has to move
through the jell, separating the longer ones at th top
and the shorter ones at the bottom. This technique is
used to separate things based on their length.
• Spectrophotometry: TF absorbs ultraviolet light most
strongly at 260 nm.
• DNA absorbs absorbs most strongly at 260 nm.
(Cancer from over exposue to sun!)
• Chemical Analysis: nitrogen:phosphorus ratio= 1.67:1.
• dna has the same ratio.
His work contradicted levin's. evine said four bases equal in
concenration.
An apple is found to have 12% of its bases in its DNA to be
thyming. What are the other %'s of the other dna bases.
38% c, g
12% a.
Major Experiment #4- Hershey and Chase
2nd to prove DNA was the stuff- 1952- in viruses!
Viruses are obligate parasites: they can only be parasties. They
cannot live indipendantly.
A virus is nothign more than a protein outside and a gentetic
material inside.
There is a T2, a T4, a T6 viruses all look alike so they called
them the T-evens.
phages: a nickname for viruses that attack bacteria.
Viruses come in different shapes and sizes.
isotope: has different mass because it has a different number of
neutrons.
The group used T-even bacteriophages to infect bacteria.
Virus= generally has 2 parts
• protein coat= capsid. the blcoks themselves are capsomeres.
• nucleic acid inside
• can be DNA or RNA inside
• if DNA, can be singel stranded (only place ever!) or
double stranded.
• can be ringlike or linear.
• Great variety= suggests multiple points of evolution.
• Viral particles may be escaped introns.
When a virus injects its dna the empty capsids fall off the cell.
The dna inside tells the host cell to make more ccopies of the
viruses and then tells the host cells to dissasemble itself.
When the empy capsid, the ghost, is done, it falls off the side of
the cell.
Virus hijeack the cell's replicating machinery an dmake new
nucleic acids and proteins. Assemble these into new viruses and
then burst out of the cell to infect new cells.
Everything pointed to the fact that DNA is the genetic material.
Two separate experiments in two different rooms.
Major Experiment #3- Chargaff's Rules 1950
Analyzed the composition of bases in differnt animals.
levine said that there were 25% of eahcof the four bases, they
were all found in equal amounts. Chargaff did not agree with
this. He said that in any given species T=A, and C=G, but they
are not all equal.
In one room, H&C grew bacteriophages in radioactive P32 isotope
(it was the viruses only source for phosphoruse, a little heavier).
In another room, they grew bacteriophages in radioactive S 35
isotope.
10/20/04 8:43 am
Chargaff found out that the numbers ary from species to
species, but are consistend ithin the species.
A=T and C=G.
You can trace the radioactive elements to see what happens to it
or where it goes.
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The sulfer went to the amino acids, tagging the protein ghost.
They then let the viruses infect the backetra and traced where
the radioactivity ended up going at th the end.
look at the picture....
End up with one batch ahaving the protein compontent tagged
with S35 and one batch having the nucleic acid component
tagged with P32.
Let S35 bacteriophages infect E.coli bacteria. Blender them a
few minutes later.
Where did radioactive stuff end up when separated? Not IN
the bacterial cells.
Repeat with P32 viruses infecting a new batch of bacteria.
Where did the radioactive stuff end upw hen separated? In the
bacterial cells!
It was the nucleic acid that got into the bacterial cells and
caused the bacterial dna to do its genetic bidding. The protein
coat stayed outside.
Proved for the second time that DNA was the genetic stuf!
Major Experiment #5- Watson & Crick, Wilkins, and
Franklin- shape of the DNA moleclue- 1953
Watson and Crick used the results of Rosalind Franklin's Xray
crystallography (pg 282) and Wilkin's research and Chargaff's
ratios to reate a model of the DNA molecule.
All four published simultaneous in Nature.
They wrote a 900 word, one page paper, classic simplicity.
"It has not escaped out notice that the specific base pairing we
have proposed immediately suggests a copying mechansim for
the genetic material."
Nobel Prize- 1962 for Watson, Crick and Wilkins, not franklin,
died in 1958 at age 37 of cancer.
COPED FROM DNA & RNA NOTES:
MACROMOLECULE 4, NUCLEIC ACIDS
micromolecule: nucleotides
all nucleotides are made of three parts:
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phospate group
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five carbon sugar, pentose
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a nitrogen contining base
1. Phosphate goup
has negative charge. if you add an H you get phosphoric
acid.
2. five carbon sugar- pentose
2 possibilties, know the numbering of carbons.
ribose: has OH on the two carbon. Used in RNA.
deoxyribise: no OH on the scond carbon, used in
DNA.
3. Nitrogen containing Bases
5 different types (see picture pages)
DNA/RNA
T/U
G/G
C/C
A/A
some are single rings: pyrimidines
some are double rings: purines
purines: adenine, DNA RNA. guanine DNA and RNA.
"puga"
pyrimidines: thymine RNA only, cytosine DNA and RNA,
uracil RNA only.
"if you sit naked on top of a pyrimid it will C.U.T. you!"
Two dehydration synthesis reactions:
phosphate: joins to the number five carbon of sugar
base: joins to the number one carbon of sugar.
Areas between t's and a's have two hyudrogen bonds, between
guaning and cytosine you have three.
A base and a sugar is known as a nucleoside (not a typo): ex:
adenine and ribose=adenosine
Other important nucleotides..
1. ATP (adenosine tri-phosphate)
3 phosphates--ribose sugar--adenine base.
The most important of all nucleotides it is the nergy transfer
molecule.
gold of the cel, energy currency, high energy bonds.
fully charged-->partially charges---> run down.
see picture pages: know how ATP works, recharged in
mtchondria like a NiCad battery.
Mitocchondria is a battery rechargeer--putsthe Pi back on.
2. NADP+ a coenzyme used in photosynthses
3. FAD+ a coenzyme used in cellular respiration.
12/9/02 1:06 pm
DNA and DNA ase made up f nuclaic aids
ribonuclaic acid
deoxyribonuclaic acid.
every nucleotide is made up of a phosphate group (a derivitive
of phoshphoric acid), the phosphate groups are negatively
charged. They hydrogens donated by DNA and RNA come
from the phosphate groups. The phosphate groups are
identical in the both.
Nucleotides: made up of phosphate groups,pentose sugar,
nitrogen containing base.
the two different pentoses are ribose and deoxyribose,
respectively.
It is imperitive for todays lecture that you learn the
numberingb for ribose and deoxyriose. Starting form tghe
oxygen, you number them clockwise around the ring, witt he
fifth carbon sticking out of the ring.
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The difference between ribose and doxyribose moleculary is
that the deoxyriose has been deoxygenized, it is missing a
hydroxyl group. "Deoxyribose is missing a hydroxyl group
off of the two primary carbon."
Everything in dna and rna are described in the terms of the
numbering system of the sugar. You must know this. The
prime is after them because they are that important. You
must learn what the prime designations are (the aprostaphe '
thing).
The last part of the nucleotides are the bases. The basic
shape difference is that one pile has two rings, while the
other only has one ring. These pile designations are
important.
purines: those that are double ringed. (drink two glasses of
urine a day for good health.)
pyrimidines: those that have only one ring. (All built one
pience at a time, no double room pyramids, etch.)
PUGA: purines: guanine and adanine.
if you sit naked on pyramids, it iwll cut you thymine,
cytosine, uracil.
The five bases are: adenine, guanine, thymine, cytosine,
uracil.
how to build a nucleotide
you have to have a pentose (deoxyribose or ribose), the
phosphate group, and the bases.
In dna you use: guanine and adanine. and tymine and
cytosine. If you see a uracil it is a mutation and it will be
removed, you will never find it tere. In your rna you have
Guanine and adanine, and cytosine and uracil. There is no
tymine in RNA. Uracil and thymine trade places.
Within a single nucleotide: the base is always hooked to the
one primary carbon and the phsophate is always hooked on
to the five primary carbon. This will always happen.
To construct the nucleotide togeterh you will have to do a
condensation reaction (times two).
Phosphates are always represented by a circle, sometimes
with a P in it.
The right and left side of the dna are built upsidedown to each
other. It's called antiparallel construction. (like shoes in a
shoebox).
The steps of a ladder are referred to as the rungs of a ladder.
The steps of a ladder are the nitrogen containing bases. The
side rails of the ladder are the alternating phosphates and
sugars.
TA, CG. a purine and a pyrimidine are always matched up on
a single step, maintaing the 2 nm constant width of the dna.
the standard width would be around three rings wide. .34
nanometers is the distance between the centers of each step.
The bonds between nucleotides are called phosphodiester
bonds. The middle of each step are held together by hydrogen
bonds, not actual covalent bonds. this is so you can unzip the
dna during mytosis. Every other bond in the dna is a covalent
bond.
phosphodiester bonds: COPOC. From theh three carbon, to
the oxygen, to the phosphorus, to the oxygen, to the five prime
carbon.
The two nucleotides that make up one secition (step and
siderails) are called a base pair. They are held together by the
hydrogen bond. If you go though and add up the weight of all
the atoms, thus the base pair is 660 daltons (amu's). The
average gene is 1200 base pairs long.
12/10/02 1:20 pm
6 billion nucleotide in one human genome
2 chains of nucleotides, side by side, hydrogen bonded together
at the bases.
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Now when you link nucleotides together
it's a polyumerization reaction.
The phophate of one nucleotide attaches to the three prime
carbon of the sugar in nuclotide above.
(number of linked-1)
Phosphate goins five prime carbon if it's own nucleotide.
The differnece between one side of the dna and the other is
that on one side the dna has the oxygens pointing up, while
on the other side the oxygens are pointing down.
If you look at the dna like a ladder, there will always be a
phosphate group attached to it's own five carbon sugar in a
corner, it is then called the five prime corner. It is the top
left of hte ladder. The oxygens point up on that vertical
column. The bottom left corner are the three prime corner.
Opposite the three prime corner on the other side, since it is
reversed, is the five prime corner, you then have the three
prime on the top right of the ladder.
bluerint molecule of life
complete set of instructions for you.
complete set in every cell of your body
directs wthich proteins will be made in the cell on a daily
basis
the enetic material that directs what your babies will be
lilke
always in the nuclus, never ever leaves. The guard
proteins keep it in there at all costs.
always uses the pentose deoxyribose in it's nucleotides.
**One gene codes for one polypeptide chain. The ribosomes
will then go out and make that polypeptide chain as specified.
Shape is a double helix (a twisted ladder). Watson, Crick,
Wilkins, and Franklin determined the shape in 1954.
Side rails of ladder: P-S-P-S-P-S-P-S
phosphate sugar phosphate...
Each step (rungs) of the ladder= two bases side by side.
T with A: bound by 2 H bonds
G with C: bound by 3 H bonds
Average gene is 1200 base pairs long.
Average Mass of a base pair= 660 daltons.
base pair: two nucleotides hydrogen bonded to each other
forming one step PLUS the side rails of the dna ladder. NOT
JUST THE BASES, BUT THE NUCLEOTIDES
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Puring always hydrogens to a pyrimidine.
Rungs of ladder are always three rings wide.
wide and narrow groves.
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rungs of ladder are three ringswide
rung-rung distance .34 nm
10 steps for one complete turn of DNA
3.4 nm for one complete turn- pitch
2 nm wide
wide groove
narrow groove
There were three schools of thought regarding how dna
replicated, suggested by scietists in the 1950's.
• conservative: the double helix of the parent sptays
completely intact and a new double helix is somehow copied
off the parent strand.
• semi-conservative: one strand of the parent DNA separates
from the ohter strand. Each daughter cell gets one copy from
the parent and one new strand is made.
• Dispersive: each of the two strands is segmented apartand
each daughter cell gets parts of the both old strands and parts
that are new.
complementary, fit togetherbut are not identical.
RNA: looks like half of a dna ladder a cob messenger from
dna to the ribosmes.
T bas is never used Looks like a ladder buzz sawed down
the middle. Always use the pentose ribose in its nucleotides.
In each series of experiments they strated with bacteria that were
made of Heay Nitrogen 15N. So all the dna in their cells was
made of heavy nitrogen.
If the bacteria's DNA was centrigued at this point it woudl sink
tot he bottom.
10/26/04 8:39 am
Major Experiement #6-Messelson- Stahl
Nitrogen has two isotopes and nitrogen is a key element in
DNA.
Regular 14N- light nitrogen (red)
and 15N- heavy nitrogen (blue)
Review of how centrifuges work. If a mixture is placed in a
centrifuge and spun down, The items will layer out: most
dense being at the bottom of hte tube.
Cesium chloride can be made usin vaious isotopes of Cs and
Cls so that a whole range of densities are obtained. This is
great becausethe range of desnisites of the CsCl mixturer
matches the range of densities of DNA made by using light and
heavy nitrogen in bactera.
A sample of DNA can be centrifuged with CsCl and the various
different DNA's will layer out in the CsCl mixture as bands.
THe heaviest DNA willd rop to near the bottom of a CsCl
gradient tube forming a visible line when it finds CsCl that
matches its density. DNA made of both light and heavy will
form a line in the middle of the CsCl gradient tube and the
DNA made entirely of light NItrogen will form a band near the
top of the CsCl tube.
10/27/04 8:21 am
CsCl is often used as a gradient mateiral when centrifuging
dna because it is very close in mass.
They let the bacteri replicate twice in a media that only had light
nitrogen available for DNA fabricationa nd then spun the DNA.
red= regular, light nitrogen
blue= modified, heavy nitrogen
If the conservatives were correct, this is what ould have
ahppened.
Original heavy dna of parent: ||
First generation: || ||
Second generation: || || || ||
When the DNA from the second generation is centrifuged it
would form three bands in the light end (all made of the light
N14) and one band at the heavy band consisting of the osle
heavy dna.
3 cells woudl have DNA made entirely out of light nitrogen
and one would have original DNA made out of heavy DNA
If the semi-conservatives were correct:
Original heavy dna of parent: ||
First generation: || ||
Second generation: || || || ||
When centrifuged it would form two light weight dna band
and two intermediate weight dna bands.
Two fof the cells oulw have dna made neitrely out of new
light nitrogena nd two cells would have DNA made of a
mixture of the heavy and light nitrogen.
If the dispersives wer ecorrect, this is what would have happened
When you want to find out the density fo a particular material
of what youa r working with, you put the sample at the top of a
CsCl tube and centrigfuge it. The sample will then migrage
down the CsCl layers until it finds the layer where it has the
same density. Then it forms a band in the test tube. Then, by
using hte scale at the edge of the test tube, you can determine
the density.
Original heavy dna of parent: ||
First generation: parts of both red and blue
Second generation: more mix of red and blue
When the dna from the second generation s cenrigued the dna
would form four band sin the middle.
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All for cells would have dna that was made of a mixture of
the ligth and heavy nitrogen.
When they actually ran the experiemnt, the semi-conservatives
were correct. Sweet experimetn: the resutles were definitive,
leaving no room for debate.
Two generations of bacteria allowed to grow before centrifugin
because otheriwse the semi-conservative and dispersive
theories woudl produce the same results.
10/28/04 8:15 am
(copy DNA replication notes here)
yeah3/21/03 11:28 am
6.
Movement is bi-directional the bubble grows in both
directions.
7.
the points on the ladder where the hydrogen bonds
between the bases are being opened are called Replicating forks.
8.
DNA nucleotides must join on to a 3' OH above it. First
nucleotide has a problem. there is not 3'OH to join on to. DNA
strands must always build 5' to 3'.
The incoming nucleotide that is supposed to be built next comes
in as a tri-phosphate nucleotide. The same process that powers
atp hapens to the tri-phosphate nucleotide. They then drop off a
pyrophosphate, to handle the condensation reaction.
9.
So… RNA nucleotides must be put in place first to
supply the 3' OH for the DNA nucleotides to hook onto Look at
your detail picture. About 10-12 RNA nucleotides start the new
strand. these are called an RNA Primer.
messleson and stahl: semiconservative replication.
DNA REPLICATION
DNA replication takes place during the S (synthesis) part of the
cell cycle.
1.
Helicase: opens hydrogen bonds of DNA ladder to
form a replicating bubble at the origin of replication. which
is rich in T's and A's. Spends two ATP/per bond to open.
breaks the double helix, pulls apart the hydrogen bonds. often
end up with two forks, (replication forks). the place where
helicase started is the origin of replication. the entire open
area is the replication bubble. Spends two atp per bond to
open.
2.
There is one replicating bubble in prokaryotesmultiple replicating bubbles in Eukaryotes. you have many
origins of replication, sequences with lots of T and A.
3.
Eukaryotes build new complimentary DNA- 50
nucleotides/second.
4.
Prokaryotes build new complimentary DNA- 500
nucleotides /second.
Why the difference in rates???
they do it alot faster than eukaryotes. they are much faster
because they don't' live as long as eukaryotic cells and because
prokaryotic cells do not have as many error checking
mechanisms as eukaryotes.
One out of every ten million base pairs in eukaryotes is
incorrect. in prokaryotes it is one ouut of every thousand/ten
thousand.
bacteria has a SOS strategy: if bacteria get into a very bad
situation they will crank up this rate and make even more
mistakes. they do this so that hopefully one of hte mistakes
will make them better off to handle the dire situration that they
are in.
5.
Like kite string being pulled apart in the middle of a
strand, DNA would bend and kink while being unwound if the
topoisomerase did not work ahead (upstream) of the helicase
relieving the stress. prevents the tension of the dna molecule by
allowing it to spin.
The RNA nucleotides cannot stay there forever and must later be
cut out and replaced with DNA nucleotides.
10.
RNA primase is the enzyme which places the RNA
primer in position.
11.
excisions endonuclease "cuts" out the RNA nucleotides
and
12.
DNA Polymerase puts the correct DNA nucleotides in
place and...
13.
DNA Ligase will "patch" the strand back together (fixes
phosphodiester bonds!) the Elmer's glue of enzymes.
14.
One new side is easy to build. One RNA primer and then
the process continues to build 5'-3'. The strand is called the
leading strand.
easy side: leading strand
hard strand: lagging strand
15.
The other side is tougher. It must keep putting in RNA
primers as the helix opens up and makes sites available. The
primers must keep being removed and DNA patched in to fill the
spaces. This is called the Lagging Strand. the short little
segments of DNA that can be fabricated and eventually patched
together are called Okazaki Fragments.
16.
The Okazaki fragments in prokaryotes are typically
1000-2000 nucleotides long. In eukaryotes they are 100-200
nucleotides long.
17.
Additional point. As the DNA helix is opened by the
helicase enzyme, it would quickly close back up before the new
complimentary nucleotides could be placed if they weren't held
open. Single Stranded Binding Proteins do this job.
18.
Proofreading: DNA polymerasae also checks to be sure
the correct nucleotide was placed in the growing chain. It is the
number one proofreading enzyme in DNA replication.
19.
The new DNA nucleotides that are going to be placed in
the growing strand float in as tri-phosphate nucleotides. The
extra two phosphates (P~P) are removed by DNA polymerase and
supply the energy for their condensation into the strand.
DNA Replication in Prokaryotes
Special Points
As you know, bacteria usually replicate by binary fission.
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The ring of DNA is attached at one point to the cell
membrane.
An origin of replicating starts opening up into a replicating
bubble and the ring is duplicated as described above.
This method is called "theta" replication because it kinda
looks like the Greek letter theta while it is happening.
it takes about ten to twelve nucleotides to cause the electrostatic
interactions to cause rna primase to fall away from the chain.
bacteria are not conservative with their genes.
3/26/03 12:58 pm
News Flash!!! Bacteria sometimes have sex!
It's called conjugation. and that long ting between them is
called a pilus. The shorter spikes are usually called fimbrae.
fimbrae are barbed, to hold onto the surface so that fluids
running by do not wash off the bacteria.
there is a certain gene that allows the bacteria to make the
spikes.. the long one is the pilus, the short ones are fimbrae.
the bacteria that can give bacteria are the males.
Other news: besides the regular ring chromosome of DNA in a
bacteria, they usually ahve smaller circles of extra DNA called
plasmids.
If a bacteria has fertility factor (F+), it has the genes for growing
a pilus. (And is known as the male partner).
When bacteria conjugate, they do not use theta replication
Instead, they use the rolling circle method. This allows multiple
copies of the chromosome or plasmid to be made at once in one
long strip an then injected through the pilus to the mating cell.
Fast quick method of dispersing resistance.
a nick develops in the outer layer. Then the outside strats to roll
off and the outer side of the latter is replaced by new dna. then
the ousdie layer is attached to a its freflective layer in the other
cell in a striaght strand. If there are multiple in a line, they are
calle dconcatamers.
Plasmids• carry anywhere from 2 to 10 genes on them.
• a rare few have been found with thirty genes in them.
• cells can have anywhere from a couple to fifty or more
plasmids in them.
• some pop into the bacterial chromosome = episomes.
3/31/03 11:35 am
when the bacteria replicates the plasmids sometimes replicate
as well.
Drug resistance is also passed from bacteria to bacteria this way.
Serious medical implications.
•
concatemer: a piece of the replicated dna that is one entire
revolution (genome). plasmids end up getting alto of genes that
are on the genome. they jump in and out as episomes. there is
alot of genetic variation.
•
•
some plasmids only replicate when the ring chromosome
replicates.
Other plasmids replicate on their own schedule.
Important genes they might carry:
Drug resistance
fertility factor (F+) if you have f+, you are a male, if you are
F-, you are a female. during conjugation plasmids can be
transferred from one bacteria to another. F+ has gene to
make a pilus.
If an F- cell (female partner) receives the fertility factor plasmid
from conjugation it then becomes a F+ cell.
Sobering thought: maleness is contagious
because plasmids are sent over so easily it is easy to have
antibiotic resistance.
The dna comes out like a two ply sheet of toilet paper as opposed
to a replication bubble.
3/24/03 1:16 pm
know:
helicase
topoisomerase
rna primase
dna polyermase
dna libase
excision endonuclease
3/25/03 1:15 pm
helicase starts at the point of origin!
single stranded binding proteins keep the helix from reforming.
they actually cover over the half strand and thus cover where
the hydrogen bonds would be and it keeps the strand from re
helixing.
the primer is about ten to twelve units in length!
10/29/04 8:34 am
Know for the exam:
• dna historical experiments
• all six
• timeline
• dna fine structure. dimensions, how it is assembled. which
nucleotides hook together.
• messelson and stahl
• dna replication
• prokaryotic
• eukaryotic
exam on wednesday
7