Sequences and their Properties
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Transcript of Sequences and their Properties
Sequences and their Properties
NucleotidesNucleotides
DNADNA A, T, G, CA, T, G, C
RNARNA A, U, G, CA, U, G, C
AnnealingAnnealing
Nucleic acids can base pair with their Nucleic acids can base pair with their reverse complement sequencereverse complement sequence
Two opposing forces affect Two opposing forces affect annealingannealing Hydrogen bonds favours Hydrogen bonds favours
annealingannealing Phosphate groups favours Phosphate groups favours
denaturationdenaturation
Annealing-Melting Point (Tm)Annealing-Melting Point (Tm) The Tm is the temperature at The Tm is the temperature at
which 50% of the nucleic acid which 50% of the nucleic acid molecules are in a single stranded molecules are in a single stranded state (or double stranded)state (or double stranded)
The Tm is a function of:The Tm is a function of: Percentage G:CPercentage G:C Ionic composition of the environmentIonic composition of the environment The percentage of complementarityThe percentage of complementarity
Estimate of TmEstimate of Tm =2(#A:T) + 4(#G:C)=2(#A:T) + 4(#G:C) 4
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Tm Vs percentage G:C
70 80 90 100
0
50
100
% D
oubl
e st
rand
ed
Temperature (C)
(38%) G+C(52%)
(58%)
(66%)
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Tm Vs Conc. of Positive Ions
70 80 90 100
% D
oubl
e st
rand
ed
Temperature (C)
(0.1M NaCl)
(0.2M NaCl)
(0.5M NaCl)
0
50
100
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Tm Vs percentage of Complementarity
70 80 90 100
% D
oubl
e st
rand
ed
Temperature (C)
(25%)
(50%)
(100%)
0
50
100
StringencyStringency
Percentage of complementarity Percentage of complementarity required to allow the formation of stable required to allow the formation of stable duplexesduplexes
The Tm influences the stringency The Tm influences the stringency conditions required to allow annealingconditions required to allow annealing A high stringency requires a high level of A high stringency requires a high level of
complementaritycomplementarity
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GATCCGGTTATTA vs GATCCGGTTATTA CTAGGCCAATAAT CTTGGACGATAAT
Parameters that Influence Parameters that Influence StringencyStringency
[salt] = High stringency [salt] = High stringency Temperature = High stringency Temperature = High stringency [salt] = ? [salt] = ? Temperature = ?Temperature = ?
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4. Hybridization with 4. Hybridization with FreeFree Probe Probe
Wash
Detection: Detection: AutoradiographyAutoradiography
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Properties of the ProbeProperties of the ProbeComplementarity
Complete or partial?Complete; ideal; 100% complementarity
Partial continuous; acceptable100% complementarity
Partial discontinuous; more difficutPartial complementarity
Hybridization StringencyHybridization Stringency
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The ProbeThe Probe
Labelled DNA or RNA moleculeLabelled DNA or RNA molecule
Single strandedSingle stranded
Strand specific (sense specific)Strand specific (sense specific)
Double strandedDouble stranded
Strand non-specific (sense non specific)Strand non-specific (sense non specific)
Digoxygenin Labelled ProbeDigoxygenin Labelled Probe
Indiret detection
S S S S
MembraneTarget
D D D D D D D D Probe+ Dig
ENZ ENZ ENZ ENZ
Ab-Dig conjugatedPeroxidase
X ray film
Hybridization SignalsHybridization Signals
HybridizationHybridization SpecificSpecific Non specificNon specific
BackgroundBackground Binding of probe to membrane Binding of probe to membrane Binding of Ab to membraneBinding of Ab to membrane
Decoding the Genetic Decoding the Genetic InformationInformation
Information encoded in nucleotide Information encoded in nucleotide sequences is contained in discrete sequences is contained in discrete unitsunits The genesThe genes
The information contained in the The information contained in the genes is genes is transcribedtranscribed to generate the to generate the RNAs and then decoded (RNAs and then decoded (translatedtranslated) ) to generate the proteinsto generate the proteins
Protein Coding SequencesProtein Coding Sequences Protein containing sequences Protein containing sequences
contain ORFscontain ORFs Start – ATGStart – ATG Stop – TAG, TGA, TAAStop – TAG, TGA, TAA
Transcription - TranslationTranscription - Translation
Transcription: RNA pol
Translation: Ribosomes
NH3-M-T-R-S-W-G-L-I-S-I-COOH
ORFsORFs All double stranded sequences All double stranded sequences
necessarily have 6 reading framesnecessarily have 6 reading frames
How many ORFs does this sequence have?
ATGCCGATTAGA>TGCCGATTAGAG>GCCGATTAGAGA>
<CTGTCGGTAATT<TCTGTCGGTAAT<CTCTGTCGGTAA
5’-ATGGCGATTAGAGACAGCCATTAA-3’3’-TACTGCTAATCTCTGTCGGTAATT-5’
HomologuesHomologues
Gene sequences that possess a Gene sequences that possess a common ancestor common ancestor Homologues share a high level of Homologues share a high level of
identityidentity IdentityIdentity
Percentage of bases or amino acids that Percentage of bases or amino acids that are the same between different are the same between different sequencessequences
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Nucleotide HomologuesNucleotide Homologues
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77% identity
DNA sequences with greater 70% DNA sequences with greater 70% identityidentity Ex. A homologue of the human Ex. A homologue of the human
hemoglobin gene is found in soyahemoglobin gene is found in soya
G.G.T.G.A.G.G.G.T.A.T.C.A.T.C.C.C.A.T.C.T.G
G.G.T.C.A.G.G.A.T.A.T.G.A.T.T.C.C.A.T.C.A.C
* * * * * * * * * * * * * * * *
Protein homologuesProtein homologues
Protein sequences with greater Protein sequences with greater than 25% identitythan 25% identity Ex. A protein homologue of the Ex. A protein homologue of the
human hemoglobin is found in soya human hemoglobin is found in soya
23Percentage identity: 28%
G A R G G W LG.G.T.G.A.G.G.G.C.A.T.C.A.T.C.C.C.A.T.C.TG.G.T.C.A.G.G.A.C.A.T.G.A.T.T.C.C.A.T.C.A G T P M I W E
HomologuesHomologues
Orthologues :Orthologues : Homologues found in different Homologues found in different
organismorganismss which have a common which have a common ancestor ancestor
Duplication followed by speciationDuplication followed by speciation
Paralogues : Paralogues : Homologues found within the same Homologues found within the same
speciesspecies Duplication prior to speciationDuplication prior to speciation
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MutationsMutations
Point MutationsPoint Mutations Missense - Neutral Synonymous/Silent :Missense - Neutral Synonymous/Silent :
Base change that does Base change that does NOTNOT change the amino acid change the amino acid codedcoded
Ex. AGG → CGG both ArgEx. AGG → CGG both Arg Missense - Non-Synonymous - Conserved:Missense - Non-Synonymous - Conserved:
Base change results in a different but similar amino Base change results in a different but similar amino acidacid
Same charge and shapeSame charge and shape Ex. AAA → AGA Lys to Arg both basic amino acidsEx. AAA → AGA Lys to Arg both basic amino acids
Point MutationsPoint Mutations Missense - Non-Synonymous-Semi conserved:Missense - Non-Synonymous-Semi conserved:
Base change resulting in a different but similar Base change resulting in a different but similar amino acidamino acid
Same shape but different chargeSame shape but different charge Ex. CGC → CUC Arg (Polar) to Leu (Non-polar)Ex. CGC → CUC Arg (Polar) to Leu (Non-polar)
Missense - Non-Synonymous - Non conservedMissense - Non-Synonymous - Non conserved Base change resulting in totally different amino Base change resulting in totally different amino
acidsacids Different shape different chargeDifferent shape different charge
Point MutationsPoint Mutations Nonsense point mutation:Nonsense point mutation:
Base change resulting in the creation of a Base change resulting in the creation of a premature stop codon within the ORFpremature stop codon within the ORF
Causes premature translation terminationCauses premature translation termination Truncated proteinTruncated protein
Indel – Insertion or deletion of a single base Indel – Insertion or deletion of a single base within the ORFwithin the ORF Changes reading frameChanges reading frame Changes protein sequenceChanges protein sequence May cause premature terminationMay cause premature termination