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10/14/04 8:25 am • What is the Genetic Stuff? • 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. • • • • • 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. 1 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. 2 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: • phospate group • five carbon sugar, pentose • 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. 3 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. • • • • • • • 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 4 Puring always hydrogens to a pyrimidine. Rungs of ladder are always three rings wide. wide and narrow groves. • • • • • • • 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. 5 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. 6 • • • 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