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NucleicNucleicAcidsStructureandFunctionAcidsStructureandFunction
Dr. Atif H. Khirelsied
De artment of Biochemistr
Faculty of Medicine
International Universit of Africa
atifkhirelsied@gmail
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Thelearnin ob ectives
. .
2. Explainthesignificanceofspecificbasepairing.
. e ne
e
ma n
proper es
o
.4. Definethecentraldogmaofmolecularbiology.
5. Distinguishbetweensingle strandedanddoublestranded
nucleicacids.
6. Exp aint emeaningo enaturationan reannea ingo DNA.
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.
.
DNAcontains
the
instructions
for
creation
and
functioning
,
Template
for
replication.
Codesforproteins.
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Thecentraldogmaofmolecularbiology
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The WatsonCrickstructureofDNA
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The WatsonCrickstructureofDNA
1. Itisadoublestrandedrighthanded
.
2. Eachstrand
is is
a
ol merof
2
deoxyribonucleotideslinkedby3'
5'phosphodiesterlinks.
3. Thenitrogenousbasesinthe
, , , .
4. Thebases
in
the
two
com lementar
strandsarespecificallypairedandheld
together byhydrogenbonds.
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The WatsonCrickstructureofDNA
5. Thetwostrandsarepolar andanti
.
6. Thebases
are
lanner and
perpendicular totheaxisoftheDNA
molecules.
7. ThewidthoftheDNAmoleculesis2nm
,
turnis3.4nm(34A).
8. Thegeneticinformationresidesinthe
sequenceofbasesintheDNAstrands.
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The WatsonCrickstructureofDNA
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ThestructureofDNA
DNAexistsascircularmoleculeinsomeorganismssuchas
bacteria,bacteriophages,andmanyDNAcontaininganimal
.
CircularDNA
molecule
of
bacteriaChromosome
(DNA)
of
eukaryotic
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DNAdenaturationof
Denaturation isthe
meltingof
double
stranded
ogenera e wos ng e
strands.
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ThedenaturationofDNA
Denaturationmayresultfrom:
HeatingaboveitsTm.
HighpH
Organicsolvents (dimethyl sulfoxide).
Lowerin thesaltconc.oftheDNAsolution
Viscosit ofDNAsolutionsdecreasesondenaturation.
denaturation)
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The ReannealingofDNA
eannea ng s ere orma ono e ou es ran e
DNA.
ViscosityofDNAsolutionsincreasesonreannealing.
Hyporchromicity (decreasedabsorbanceofUVon
reannealing)
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The RNAstructurediffersfromthatofDNA
TheRNAsarepolymersofribonucleotides linkedtogetherby
3'5'phosphodiester bonds.
RNAssharemanystructuralfeatureswithDNAbuthavesome
specificcharacteristics,
these
are:
itcontainsriboseratherthandeoxyribose
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The t esofRNA
. essenger s m s .
2. TransferRNAs
tRNAs . Prokaryotes
and
3. RibosomalRNAs(rRNAs).eukaryotes
. sma nuc ear sn .
5. microRNA (miRNA).
6. smallinterferingRNA(siRNA)
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The messen erRNA mRNA
Heterogeneousinsizeandstability.
Carriesthe
codons specifying
amino
acid
sequences
in
proteins
Actas
templates for
protein
synthesis.
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Eukar oticmRNAshaveseveraluni ue ro erties
. e erm na scappe y me y guanos ne
triphosphate.
2. Haspoly(A)tailinthe3'terminals.
7mG
A
A
A
A
A
A
AmRNA
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Eukar oticmRNAshaveseveraluni ue ro erties
Eukaryotics issynthesizedaspremRNA(heteronuclear RNA)whichcontaininterveningregions(Introns).
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TransferRNA(tRNA)
.
formationofintramolecularbasepairs.
Havecloverleafshape(hairpin).
Transferaminoacidsintothe
.
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RibosomalRNA(rRNA)
Theyhavearibozyme function,the28SrRNAcatalyzethesynthesisof peptidebonds(peptidyl transferase).
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RibosomalRNA(rRNA)
Itisanucleoproteinparticle.
Themammalianribosome,
hasasedimentation
velocity
of80S(Svedbergunits).
ons stso arge an
small40Ssubunits.
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SmallnuclearRNA(snRNA)
Alargenumberofhighlyconservedsmallstablemolecules
ofRNAfoundineukaryoticcells.
Themajorityofthemexistsasnucleoproteinsdistributedin
boththenucleusandthecytosol.
TheyareinvolvedinmRNAprocessingandgeneregulation.
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microRNA (miRNA)
Are shortRNAmoleculesfoundineukaryoticcells.
Havevery
few
nucleotides
(an
average
of
22)
compared
with
otherRNAs.
.
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SmallinterferingRNA (siRNA)
Also knownasshortinterferin RNAorsilencin RNA
Aredouble
stranded
RNA
molecules
Have2025nucleotidesinlength
Theyinterfere
with
the
expression
of
aspecific
gene.
