DNA

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DNA

Chapter 16 and 17 Biology II

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Meselson and Stahl Experiment

http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.html

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Search for the Genetic Material

Scientists knew the hereditary material containedProtein—macromolecules, very diverse, specificNucleic Acids—little known

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ExperimentsGriffith--1928 Studied Streptococcus pneumonia Two strains of pneumococcus:S-strain Smooth, polysaccharide capsule;

pathogenic R-strain Rough, no capsule, not pathogenic

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Griffith’s ExperimentsFour Sets of Experiments: 1. Live S injected into

mice

2. Live R into mice

3. Heat killed S

4. Heat killed S+R

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Griffith’s Experiment

Live S cells retrieved from Group 4R strains had acquired from dead S the ability to make polysaccharide coats Transformation *protein is NOT the transforming

agent b/c heat denatures protein

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Griffith’s Experiment

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Hersey and Chase Experiments--1952

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#Bacteriophage Virus that infects bacteria

Consists of : Protein coat

Viral protein tagged with 35S With DNA

DNA tagged with 32P

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Hersey and Chase Experiments--1952

S was incorporated into bacteriophage proteinP was incorporated into bacteriophage DNA

Labeled T2 phages were allowed to infect separate samples of E.coliCultures were agitated to shake loose phages on outside

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Hersey-Chase ExperimentsWhat happened?Radioactivity in pelletP in DNA of bacteriaWhat does it mean?Radioactivity in supernatantS in protein coat of virus

PROTEIN is NOT the hereditary materialDNA IS the hereditary material

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Additional evidence that DNA is the genetic

material1. Eukaryotic cell doubles DNA prior to

mitosis2. During mitosis DNA is divided between

daughter cells3. Diploid cells have 2x the DNA of haploid

cells4. Chargaff’s Rule (using paper

chromatography) A=T; G=C

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Watson-Crick Double Helix1953—Three groups race to find the answer:

1. Linus Pauling Cal Tech2. Maurice Wilkins and Rosalind

Franklin Kings College London3. James Watson and Francis Crick

Cambridge University

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Rosalind Franklin*Watson went to Cambridge saw x-ray crystallography (Rosalind Franklin)From photo, Watson concluded: DNA is uniform 2nmBases are .34 nm apart with 10 bases making a full rung at 3.4 nm

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DNA Nitrogenous basesPurines Adenine and

guaninePyrimidines Thymine Cytosine

A-T (2 hydrogen bonds)G-C (3 hydrogen bonds)

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DNA StructureNucleotides line up A-T; G-CEnzymes link the nucleotides together with P-S groupsEach strand=one old and one newly created strand

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DNA—double Helix

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Purines and Pyrimidines

PurinesPyrimidines

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DNA ReplicationDNADNAhttp://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

Origin of replicationWhere replication beginsReplication

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Enzymes

1. DNA polymerase• Elongation on new DNA strand 5’3’

only

2. DNA ligase • Joins fragments into single strand by

phosphodiester bonds

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Enzymes

3. DNA helicase Unwind and unzip DNA

4. RNA primase Need to begin the process of replication

b/c polymerase cannot begin adding nucleotides unless there is one there

Binding proteins—keep the strands apart

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DNADNA strands are antiparellelSugar-phosphate backbone run in opposite directionsLeading strand--Phosphates are attached to #5 carbon 5’

Overall direction of replication

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Leading StrandReplicated continuously

5’-3’ direction

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ReplicationDNADNA

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Lagging StrandLagging strand—phosphates are attached to #3 carbon 3’Replicated in pieces in 5’-3’ directionPieces are called Okazaki fragments

Leading strand

Lagging strand

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Replicate this!TAC TTA AAA CTT CGA CTA TTT ATT

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http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

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•Thinkwell's DNA Replication

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Semiconservative Model of DNA

1950 Meselson and StahlTwo DNA strands separateEach strandtemplate for complementary strand

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Chapter 17

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TranscriptionDNARNA

Two blue/purple strandsDNARed BlobRNA polymeraseGreen strandmRNAWhere occur?

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Transcriptionhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

DNA base sequence below: TAC TTA AAA CTT CGA CTA TTT ATTTranscriptionDNARNATranscribe top line

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RNASingle strandedNucleotide:1. 5-C sugar

Ribose2. Phosphate group3. Nitrogenous bases

Uracil in place of Thymine (A-U)

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Three types of RNA1. mRNA

Carries the message to ribosome2. tRNA

Specific for a particular amino acid3. rRNA

Two subunits compose the ribosome

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RNAFunction: To synthesis proteins Translation or protein synthesisStructure: Polymer of nucleotides Single strand 3 types

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rRNArRNA—ribosomal RNA Two subunits

Ribosome “reads” mRNA and produces a polypepide

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3 Types of RNA1.mRNA Messenger RNA

Single strandServes as a template (pattern for translation)

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3 Types of RNA2. tRNA Transfer RNA

20+ types of tRNACloverleaf shapeEach tRNA is specific for an amino acid

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3 Types of RNA3. rRNA Ribosomal RNA

Globular2 parts compose the ribosomeWhere are they made?

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mRNA--CodonsCodon

sequence of 3 nucleotide bases on mRNA

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TranscriptionEnzyme: RNA polymerase (3 kinds in eukaryotes)“unzips” DNA and adds RNA nucleotides in the 5’ 3” direction

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TranscriptionPromotor Site where the

polymerase attaches

Termination site Site where

transcription endsTranscription Unit The stretch of

DNA transcribed

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TranscriptionIn eukaryotes, the mRNA is modified after transcriptionA 5’ cap is added (guanine nuicleotide)Poly A tail (adenine)50-250 nucleotides long

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RNA splicing“cut and paste” of original RNA molecule that was synthesized

RNA splicingIntrons Noncoding

regions of RNA Interspersed

between the coding regions

Exons Coding regions

that will exit the nucleus and be translated

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TranslationRNA proteinStructure of a ribosome Protein and

rRNA Most common

form of RNA Ribosomes are

formed in the nucleolus

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TranslationThree stages of translation

1. Initiation2. Elongation3. Termination

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InitiationSmall ribosomal subunit binds to both the mRNA and the tRNALarge ribosomal subunit attaches

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ElongationCodon recognition--mRNA and tRNA form hydrogen bonds at the “A” site of the ribosomePeptide bond forms between amino acid at the “A” site and the growing polypeptide at the “P” siteTranslocation Ribosome moves the

tRNA with polypeptide from the “A” to the “P”

Exit site

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TerminationTranslation continues until “stop” codon on mRNA—UAA, UAG, or UGAPolyribosomesMultiple ribosomes translating the same rRNA (polysomes)

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Genetic Code Tablecodons

Universal for almost all organisms P. 308 in text Use it to

decode the base sequence on the next slide

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Translate This

•http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

•AUG AAU UUU GAA GCU GAU AAA UAA

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Translationhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Animations

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Translation—mRNApolypepide

mRNA codons are translated into a specific amino acid sequence

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Central DogmaDNA-->RNA-->Protein

Some organism have RNA as main nucleic acid and can go from RNA to DNAEx. Aides virushttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/lifecyclehiv.html

DNARNA

Protein

Transcription

Translation

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Interactive Translation Websites

http://bioweb.uwlax.edu/GenWeb/Molecular/Theory/Translation/translation.htm  

http://wsrv.clas.virginia.edu/~rjh9u/gif/protein.mov

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DNA packing into chromosomes

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DNA fingerprint“BAR CODE”Everybody has a different one

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C. elagans

First organism to have its complete genome mapped

Roundworm

Beadle and Tatum Experiment

One gene-one enzyme hypothesisOne gene-one polypeptide hypothesisCurrent hypothesis is one gene codes for a polypeptide rather than a complete enzyme

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MutationsMutation Any change in the

DNAPoint mutation A change in one

nitrogenous base Either a deletion,

insertion or substitution

Substitution is the least destructive

Sickle cell disease is caused by a point

mutation—a substitution

MutationsFrameshift mutations Caused by

either a deletion or an insertion

Changes the reading frame