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DNA standsfordeoxyribose nucleicacid.

DNAcontrolsthekindofcellwhichisformed(i.e.muscle,blood,nerve).

DNAcontrolsthetypeoforganismwhichisproduced(i.e.buttercup,giraffe,herring,

human).

DNAStructure

Nucleotide Structure• DNA is made up of nucleotides joined into long strands or chains by covalent bonds.• Nucleic acids are made up of building blocks called nucleotides.

Base

Deoxyribosesugar

Phosphategroup

DNA is a polymer made up of a chain of nucleotides

Each nucleotide has three parts:• simple sugar (deoxyribose)• phosphate group• Nitrogen base (adenine, guanine, thymine, or cytosine)

DNA Nucleotide Structure

AmoleculeofDNAisformedbymillionsofnucleotidesjoinedtogetherinalongchain.

PO4

PO4

PO4

PO4

sugar-phosphatebackbone

+bases

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Nitrogenous Bases

Adenine

Guanine

Cytosine

Thymine

Nucleic Acid Structure

Covalent bond between nucleotides

One nucleotide

Chargaff’s Rule[A] = [T] and [C] = [G]

Franklin’s X-rays• DNA is a helix.• Likely two strands to the molecule• Nitrogenous bases near the center of the molecule

The Work of Watson and CrickDNA is a double helix, in which two strands of nucleotide sequences are wound around each other.

The Double Helix: Antiparallel StrandsThe two strands in a DNA molecule run in opposite directions.

Thesugar-phosphatechainsareontheoutsideandthestrandsareheldtogetherbyhydrogenbondsbetweenthebases.

The Double Helix: Hydrogen Bonding Hydrogen bonds

The Double Helix: Base PairingThe two strands of DNA are held together by hydrogen bonds between the nitrogenous bases adenine and and between guanine and .

thyminecytosine

Nucleotide Sequence

• Living organisms are different due to the differences in sequences of bases.– For example, the code ATTGAC would code

for a different protein than TCCAAA

• Because the order of these bases is so important, DNA must carefully replicateitself when the cell divides to ensure an exact copy is passed on to each daughter cell

• Sphaseduringinterphase ofthecellcycle

• Nucleusofeukaryotes• DNAreplicationtakesplaceintheSphase.

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HowisDNAcopied?

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DNAReplication• BeginsatOriginsofReplication• TwostrandsopenformingReplicationForks(Y-shapedregion)

• Newstrandsgrowattheforks

ReplicationFork

ParentalDNAMolecule

3’

5’

3’

5’copyright cmassengale

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DNAReplication

• Asthe2DNAstrandsopenattheorigin,ReplicationBubblesform

• Prokaryotes(bacteria)haveasingle bubble• EukaryoticchromosomeshaveMANY bubbles

Bubbles Bubbles

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DNAReplication• DNAisunzippedandunwoundbytheenzymehelicase

• TheenzymePolymeraseattachesandreadstheDNA

• DNAnucleotidesfindtheircompliments oneachsideoftheDNAstrand

• Newbaseskeepattachinguntiltwo identicalmoleculesofDNAarecompleted.

• Mitosis wouldthenfollowwhereeachdaughtercellwouldbegivenmatchingcopies oftheoriginalDNA

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DNAReplication• Before newDNAstrandscanform,there

mustbeRNAprimers presenttostarttheadditionofnewnucleotides

• Primase istheenzymethatsynthesizestheRNAPrimer

• DNApolymerasecanthenaddthenewnucleotides

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DNAReplication• DNApolymerasecanonlyaddnucleotidestothe3’ endoftheDNA

• ThiscausestheNEWstrandtobebuiltina5’ to3’ direction

RNAPrimerDNAPolymerase

Nucleotide

5’

5’ 3’

DirectionofReplication

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ProofreadingNewDNA

• DNApolymeraseinitiallymakesabout1in10,000basepairingerrors

• Enzymes proofreadandcorrectthesemistakes

• ThenewerrorrateforDNAthathasbeenproofreadis1in1billionbasepairingerrors

DNA- CrashCoursehttps://www.youtube.com/watch?v=JIPw-Bd0WGgStart@0:50-3:42

ReplicationForkAnimation• http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::

535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

5’-3’

• https://www.youtube.com/watch?v=p835L4HWH68

SpeedofDNAReplication!

• http://www.hhmi.org/biointeractive/dna-replication-basic-detail