dna notes revised edition!
TRANSCRIPT
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DNA
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Griffith’s Experiment
Fredrick Griffith1928 British scientistWanted to see why people
got sick from bacteria (pneumonia)
Used mice and a strain of disease causing bacteriaHarmless strain had rough
edges when it was grown on a petri dish
Disease –causing strain had rough edges when grown on a petri dish
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S-strain of bacteria killed mouse (smooth)R-strain does NOT kill mouse (rough)Heat kills the bacteria
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What Griffith’s Experiment Proved
Griffith’s hypothesis:When live, harmless bacteria and heat-killed
bacteria are mixed, the heat-killed bacteria passed on disease-causing information to the live cells of the harmless bacteria, causing harmless bacteria to “transform” into bad bacteria
Transforming FactorThis factor was probably a gene because he
noticed that the offspring inherited the disease as well
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Avery’s Experiments: DNA is the Transforming Factor
American biologist Oswald Avery, 1944 Was transforming factor DNA or Protein? Took Griffith’s heat-killed bacteria and good bacteria and
made an extract (aka a juice) Treated this extract “protein-destroying enzymes” Injected mice with the treated extract
Did the bacteria still function and kill the mice?Yes, the bad bacteria still transformed the harmless
bacteria…therefore protein did NOT contain the “transforming factor”
Treated Griffith’s deadly bacteria and harmless bacteria with “DNA-destroying enzymes”
Did they still function?No, the bacteria was not transformed, therefore, DNA had to
be the transforming factor
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Avery’s ConclusionDNA is the cell’s genetic materialScientists were still skepticalProtein is made of 20 a.a. and DNA is only 4
nucleotides…didn’t make senseThey thought….”DNA is too simple!”
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Hershey and Chase’s Experiments
1952, American biologists Alfred Hershey and Martha Chase
Which is the hereditary material: Protein or DNA ???
Conducted Experiments using viruses Viruses
Package of nucleic acid wrapped in a protein coatNot made of cellsCan only reproduce by infecting living cell with
its genetic infoGenetic info of virus then tells the cell’s
organelles to make more virusesBacteriophage (phage)-virus that infects
bacteria…literally means “bacteria eater” Virus attaches to the surface of bacteria, injects its genetic
material into the bacteria, the viral genes cause many more viruses to be made inside the bacteria until the bacteria burst and hundreds of new viruses are released
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Hershey and Chase Experiment 1
Treated virus with radioactive sulfur-35 isotope (sulfur is in protein but not DNA)
Sulfur would attach to protein of virus If rad. sulfur was found in bacteria, that means it was the
protein coat of virus that contained hereditary information
Experiment 2 Treated virus with radioactive phosphorus-32 isotope
(phosphorus is in DNA but not protein) Phosphorus would attach to DNA of virus If rad. phosphorus was found in bacteria, that means it
was the protein coat of virus that contained hereditary information
Used blender to mix up bacteria and viruses Experiment 1=radioactive material was found out side
the bacteria cells Experiment 2=radioactive material was found inside
the bacterial cells
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Hershey and Chase’s Experiments
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Hershey and ChaseConclusion
The Phage’s (virus’) DNA entered the bacteria during infection but the protein did not
DNA must carry the genetic information of the virus
DNA is the hereditary material
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DNA StructureDeoxyribonucleic
AcidDNA is a polymer
made up of many monomers called nucleotides
Nucleotide contains:5-carbon sugar
called deoxyriboseRNA contains RIBOSE
sugar insteadPhosphate groupOne Nitrogenous
base (there are 4 types)
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Sugar and phosphate make up backbone (sides of ladder)
Nitrogenous bases make up steps of ladderBases are always paired (Chargaff’s rule)
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What are these Nitrogenous bases???
Make up the “steps” of the DNA ladder One Step= A Purine + A
Pyrimidine
PurinesDouble ring structureAdenineGuanine
PyrimidinesSingle-ring structureCytosineThymine (in DNA only)Uracil (in RNA only)
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Adenine (Purine) binds with Thymine (pyrimidine)TWO hydrogen bonds
Cytosine (Purine) binds with Guanine (pyrimidine)THREE hydrogen bonds
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Chargaff’s RuleErwin Chargaff, Am.
biochemistYears before Watson
and CrickPercentage of guanine
and cytosine in DNA sample were about equal…the same with adenine and thymine
Chargaff’s Rule: A=T and G=C
Rule for “base-pairing”
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Rosalind Franklin and Maurice Wilkins
Rosalind Franklin, 1950s, Brit scientist who studied DNA
Used X-ray diffraction technique to learn about structure of DNA
She noticed an X-shaped pattern
This indicated that DNA had a helical structure
She did not get a chance to publish her research…and her idea was basically stolen
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Watson and Crick23-year old American
Biologist James Watson went to work with English Physicist Francis Crick
Used information from Rosalind Franklin and Maurice Wilkins (1950’s)These two scientists used
Rosalind Franklin’s x-ray crystallography images to begin to piece together the DNA structure
Showed that there were 2 strands twisted around each other
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Watson and Crick
DNA is a double helixCreated the first accurate model of DNA
using wireBases paired up specifically with each other
b/c of hydrogen bondingComplementary base-pairing
A purine with a pyrimidineA=TG=C
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DNA StructureChromatin wrapped
around proteins called histones
Chromatin condenses to form chromosomes during replication
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This is what they already knew from the work of many scientists, about the DNA molecule:
DNA is made up of subunits which scientists called nucleotides.
Each nucleotide is made up of a sugar, a phosphate and a base.
There are 4 different bases in a DNA molecule: adenine (a purine) cytosine (a pyrimidine) guanine (a purine) thymine (a pyrimidine)
The number of purine bases equals the number of pyrimidine bases
The number of adenine bases equals the number of thymine bases
The number of guanine bases equals the number of cytosine bases
The basic structure of the DNA molecule is helical, with the bases being stacked on top of each other
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Central Dogma of Biology
DNAmRNAproteinDNA TRANSCRIBES to mRNA
Process is called transcriptionmRNA TRANSLATES to
proteinsProcess is called translationmRNA actually makes amino
acids, which come together to make proteins
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Nucleic AcidsDNA
Double strandDeoxyribose
sugarA=TG=C
RNASingle StrandRibose sugarA=UG=CUracil is the
nitrogenous base used instead of THYMINE
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DNA parent strand makes 2 daughter strands…one fast, smart daughter strand (leading) and one, slower, no-fast daughter strand (lagging)
Leading strand (runs 3’ to 5’)
Lagging strand (runs 5’ to 3’)
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How does DNA replicate itself?
Template mechanismWhat is a template???
PowerPoint presentations….Like the negative of a photograph
DNA ReplicationProcess of copying the DNA molecule
What phase of the CELL CYCLE?S-phase….
2 strands of double helix separate (Unzips)Each strand acts as a negative for making
the new complementary strandNucleotides line up one by one following
base pairing rulesEnzymes (DNA Polymerase and DNA
Ligase) link nucleotides together to form 2 new DNA strands called the daughter strands
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DNA Replication SimplifiedUnzip parent DNAAdd nucleotides to the 2 template
strands of DNADNA parent strand makes 2 daughter strands…one
fast, smart daughter strand (leading) and one, slower, no-fast daughter strand (lagging)
Leading strand (runs 3’ to 5’)Lagging strand (runs 5’ to 3’)
Attach fragments on lagging strand
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Origins of ReplicationSpecific site on DNA where
replication beginsDNA Helicase: enzyme that
binds to origin site and unwinds DNA in both directions
Copying goes outward in both directions making replication “bubbles”
Parent strands open up as daughter strands grow on both sides
Eukaryotic DNA has many origins of replication on a single DNA strandMakes copying faster
Eventually bubbles merge making two new strandsEach new strand has a part from
the original and a part from the new
Semi-conservative replicationMeans that parent of the original DNA
double helix is always kept as part of the new DNA copies
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DNA PolymerasesEnzymesMake covalent bonds between nucleotides of
the new strandsFast, accurate process
Error only one in a billion nucleotides
Brings over nucleotides to unzipped DNA strand and drops them off
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More Players in DNA Replication
DNA polymerase can only read a strand that is running 3-prime to 5-prime…DNA polymerase works non-stop
adding nucleotides onto the strand that runs in the 3’ to 5’ direction
Therefore, Only one strand is made by a smooth, and continuous process…
The other strand is put together in bits and pieces…Each little section of nucleotides
is called an “Okazaki Fragment”These are then “glued” together
to make one, continuous strand in the end by another enzyme…
DNA Ligase
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Important Enzymes
DNA Helicaseunzips
DNA PolymeraseAdds nucleotides
DNA LigaseAttaches/glues
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Central Dogma of Biology
DNAmRNAproteinDNA TRANSCRIBES to mRNA
Process is called transcriptionmRNA TRANSLATES to
proteinsProcess is called translationmRNA actually makes amino
acids, which come together to make proteins
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DNAmRNAamino acids/polypeptide chain (Proteins)
DNA codes for an RNA strand The every 3 bases on the RNA
strand code for a specific amino acidCODON: three sequential
bases that code for a specific a.a. (20 a.a. total)
Amino acid are strung together to make a protein (primary structure)
Change DNA will change RNA which will change amino acids, which change protein
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Legend: Transcription of DNA to RNA to protein: This dogma forms the backbone of molecular biology and is represented by four major stages.
1. The DNA replicates its information in a process that involves many enzymes: replication.
2. The DNA codes for the production of messenger RNA (mRNA) during transcription.
3. In eukaryotic cells, the mRNA is processed (essentially by splicing) and migrates from the nucleus to the cytoplasm.
4. Messenger RNA carries coded information to ribosomes. The ribosomes "read" this information and use it for protein synthesis. This process is called translation.
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Ala: Alanine Cys: Cysteine Asp: Aspartic acid Glu: Glutamic acidPhe: Phenylalanine Gly: Glycine His: Histidine Ile: Isoleucine Lys: Lysine Leu: Leucine Met: Methionine Asn: AsparaginePro: Proline Gln: Glutamine Arg: Arginine Ser: SerineThr: Threonine Val: Valine Trp: Tryptophane Tyr: Tyrosisne
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One Gene, One PolypeptideGeorge Beadle and Edward TatumAm. Geneticists1940sOrange bread mold, Neurospora
crassaStudied mutant strains of this mold
that could not growEach of the strains lacked a
specific enzyme needed to produce some molecule the mold needed to grow
Each strain was defective in a single, specific gene
“One-gene, one-enzyme” hypothesisThe function of an individual gene
is to dictate the production of specific enzyme
Scientists later learned that genes dictate not just enzymes, but a single polypeptide, so the hypothesis became known as the “One Gene, One Polypeptide” hypothesis
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DNAmRNAProtein
TranscriptionDifferent form of the same
messageDNA makes single stranded
RNA (U replaces T)RNA leaves nucleus
TranslationTranslate from nucleic acid
language to amino acid language
Uses codons, 3-base “word” that codes for specific a.a.“code” for an amino acid
Several codons make a “sentence” that translates to a polypeptide (protein)
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The Genetic CodeAm. Biochemist Marshall
Nirenberg began to crack the genetic code in the 1960sBuilt RNA model with uracil, called
poly U, conducted experiments with it and figured out UUU coded for amino acid phenylalanine
Scientists used his procedures to figure out the other amino acids represented by codons
Stop codons: UAA, UGA, UAGSIGNAL END OF GENETIC MESSAGE
Start codon: AUGSIGNAL TO START TRANSLATING an
RNA transcript
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Start Codons
UAAUGAUAG
Stop Codons
AUG
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Three Types of RNAmRNAtRNArRNA
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Three Types of RNA… #1mRNA (messanger RNA)
RNA transcribed from DNA templateRNA polymerase (enzyme) links RNA nucleotides
togetherModified in nucleus before if exits
RNA splicing: process in which Introns are removed and exons re joined together to make a continuous coding mRNA molecule
IntronsInternal non-coding regions of DNA and mRNASpace fillersThey are cut out of mRNA before it is allowed to leave the
nucleusProcess is called RNA splicing (processing)
ExonsCoding region of DNA and mRNA that will be translated
(Expressed)VERY important part of mRNA…it is carrying the message from
DNA (def can’t cut this out)
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Three Types of RNA…#2tRNA (transfer RNA)
The interpreterTranslate 3-letter base
codes into amino acids Carries anti-codon on one
end (three letters opposite of what is on mRNA)
Carries amino acid on other end
Anti-codon recognizes codon and attaches
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Three Types of RNA…#3rRNA (ribosomal RNA)
Found in ribosomeRibosome composed of 2
subunits:Small subunit for mRNA to
attachLarge Subunit for two tRNAs
to attach“P” site: holds the tRNA
carrying the growing polypeptide chain
“A” site: holds the tRNA that is carrying the next a.a. to be added to the chain
When stop codon (UAA, UAG, UGA) is reached, translation ends and polypeptide is released from tRNA by hydrolysis
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