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BIOL221BIOL221

Ch5(excerpt)Ch5(excerpt)

NucleicAcidsNucleicAcids

NucleicAcidsNucleicAcids

• Storeandtransfergene3cinforma3on

• Gene

• Unitofinheritancethatcodesfortheaminoacidsequenceofapolypep3de

• Makesaprotein

• GenesaremadeofDNA

• Anucleicacid

TheRolesofNucleicAcidsTheRolesofNucleicAcids

• Twotypesofnucleicacids:

• Deoxyribonucleicacid(DNA)

• Ribonucleicacid(RNA)

• DNA

• Codesforproteins

• Providesdirec3onsforitsownreplica3on

• DirectssynthesisofmessengerRNA(mRNA)

• Containsinforma3onforproteinsynthesis

• Proteinsynthesisoccursinribosomes

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mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUSCYTOPLASM

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mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement ofmRNA into cytoplasmvia nuclear pore

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2

mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement ofmRNA into cytoplasmvia nuclear pore

Ribosome

AminoacidsPolypeptide

Synthesisof protein

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2

3

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TheStructureofNucleicAcidsTheStructureofNucleicAcids

• PolynucleoFdes

• Nucleicacidpolymer

• NucleoFde

• Monomersofpolynucleo3de

• Consistsof

• Pentosesugar

• Phosphategroup

• Nitrogenousbase

• Adenine(A),Cytosine(C),Guanine(G),Thymine(T)

• Nucleoside

• por3onofanucleo3dewithoutthephosphategroup

5′ end

Nucleoside

Nitrogenousbase

Phosphategroup Sugar

(pentose)

(b) Nucleotide

(a) Polynucleotide, or nucleic acid

3′ end

3′C

3′C

5′C

5′C

Nitrogenous basesPyrimidines

Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)

Purines

Adenine (A) Guanine (G)

Sugars

Deoxyribose (in DNA) Ribose (in RNA)

(c) Nucleoside components: sugars

NucleoFdeMonomersNucleoFdeMonomers

• Twofamiliesofnitrogenousbases:

• Pyrimidines

• cytosine(C),thymine(T),anduracil(U)

• singlesix‐memberedring

• Purines

• adenine(A)andguanine(G)

• six‐memberedringfusedtoafive‐memberedring

• Deoxyribose

• SugarinDNA

• Ribose

• SugarinRNA

• Nucleo3de=nucleoside+phosphategroup

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NucleoFdePolymersNucleoFdePolymers

• Nucleo3dePolymers

• Linkedtogethertobuildapolynucleo3de

• Simplyunfinishednucleicacid

• Adjacentnucleo3des

• Joinedbyphosphodiesterbonds(covalent)

• Formbetweenthe–OHgrouponthe3′carbonofonenucleo3deandthephosphateonthe5′carbononthenext

• Createabackboneofsugar‐phosphateunits

• Withnitrogenousbasesasappendages

• ThesequenceofbasesalongaDNAormRNApolymerisuniqueforeachgene

TheDNADoubleHelixTheDNADoubleHelix

• Doublehelix

• Twopolynucleo3desspiralingaroundanimaginaryaxis,formingaDNAmolecule

• Nitrogenousbasesbondwithoneanotherinthemiddleincomplementaryfashion

• A‐T;C‐G

• Hydrogenbonds

• AnFparallel

• Twobackbonesruninopposite5′→3′direc3onsfromeachotherintheDNAdoublehelix

• OneDNAmoleculeincludesmanygenes

• Equalsonechromosome

DNAReplicaFonDNAReplicaFon

• Semi‐conservedmodel

• Oneparentstrandyieldstwodaughterstrands

• Eachdaughterstrandcontainshalfoforiginalparentstrand

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DNAandEvoluFonaryRelaFonshipsDNAandEvoluFonaryRelaFonships

• Sequencesofnucleo3desinDNA

• Passedfromparentstooffspring

• Twocloselyrelatedspecies

• AremoresimilarinDNA

• Thanaremoredistantlyrelatedspecies

• Determinedby%divergence