genetic organisation
DESCRIPTION
Genetic Organisation. In Prokaryotes. Transcrition and translation occurs in same compartment (cytoplasm) Simultaneous; m-RNAs are short-lived (afew minutes) No splicing M-RNA is not polyadenylated No IRES in eukaryotes No introns in prokayotes (except some bacteriophages). 5’-3’ direction - PowerPoint PPT PresentationTRANSCRIPT
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Genetic OrganisationGenetic Organisation
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In ProkaryotesIn Prokaryotes
Transcrition and translation occurs in same Transcrition and translation occurs in same compartment (cytoplasm)compartment (cytoplasm)
Simultaneous; m-RNAs are short-lived (afew Simultaneous; m-RNAs are short-lived (afew minutes)minutes)
No splicingNo splicing M-RNA is not polyadenylatedM-RNA is not polyadenylated No IRES in eukaryotesNo IRES in eukaryotes No introns in prokayotes (except some No introns in prokayotes (except some
bacteriophages)bacteriophages)
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TranscriptionTranscription 5’-3’ direction5’-3’ direction Any strand of DNA Any strand of DNA
can be transcribedcan be transcribed No need for helicases, No need for helicases,
topoisomerases, topoisomerases, primersprimers
RNA polymerase: 4 RNA polymerase: 4 chains 2alpha, beta, chains 2alpha, beta, Beta’Beta’
Promoter is Promoter is recognised by the recognised by the factor sigmafactor sigma
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In some cases termination In some cases termination rho rho dependent factors, which are helicasesdependent factors, which are helicases
Rho utilisation site Rho utilisation site 80-100 bp upstream 80-100 bp upstream of actual terminatorof actual terminator
In E. Coli other factors: tau, nusIn E. Coli other factors: tau, nus
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In bacteria ribosomesIn bacteria ribosomes
70 s = 50 S and 30 S70 s = 50 S and 30 S 50 S subunits: 23 S and 5 50 S subunits: 23 S and 5
S RNA moleculesS RNA molecules 30 S subunits: 16 S RNA 30 S subunits: 16 S RNA
and 21 polypeptidesand 21 polypeptides rRNA binds to m-RNA at rRNA binds to m-RNA at
spesific sequences: spesific sequences: Shine-Dalgerno Shine-Dalgerno sequence (RBS) partly sequence (RBS) partly complementary to the 3’ complementary to the 3’ end of 16 S RNAend of 16 S RNA
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tRNAtRNA
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Secretion of the proteinsSecretion of the proteins
Many proteins exert their functions on the Many proteins exert their functions on the cell surface or in extracellular cell surface or in extracellular environementenvironement they should across the they should across the cytoplasmic membranecytoplasmic membrane
GSP GSP Sec dependent pathway Sec dependent pathway Proteins utlising GSP have a specific Proteins utlising GSP have a specific
sequence at their N termini, which is sequence at their N termini, which is cleaved during the transportcleaved during the transport
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In Gram positive bacteria GSP is sufficientIn Gram positive bacteria GSP is sufficient
but ın Gram negative bacteriabut ın Gram negative bacteria
Proteins reach only to the periplasmic spaceProteins reach only to the periplasmic space
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Gram negatives have addional Gram negatives have addional mechanism: Sec dependent and Sec mechanism: Sec dependent and Sec
independentindependent
Sec dependent systemsSec dependent systems Type II secretion system: A multiprotein Type II secretion system: A multiprotein
complex transports proteins from the complex transports proteins from the periplasmic space to the outsideperiplasmic space to the outside
Type V secretion system: The proteins Type V secretion system: The proteins have an additional sequence at the C have an additional sequence at the C terminus, forming pores in the outer terminus, forming pores in the outer membrane (aototransporters)membrane (aototransporters)
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Sec independent systemsSec independent systems Types I, III and IVTypes I, III and IV
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Repair systemsRepair systems
Proof-readingProof-reading Miss-match repair: Methyle directed Miss-match repair: Methyle directed
missmatch repairmissmatch repair Excision repair:uvrA, B and C Excision repair:uvrA, B and C
endonucleases endonucleases
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Post-replication Post-replication (recombination) (recombination) repair:repair:
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SOS repair:ssDNA stimulates rec ASOS repair:ssDNA stimulates rec A Rec A downregulates lex A whic repress Rec A downregulates lex A whic repress
SOS genes (18 genes) SOS genes (18 genes) Error prone DNA repairing system Error prone DNA repairing system
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MUTATION and VARIATIONMUTATION and VARIATION
BActerial populations are not homgeneousBActerial populations are not homgeneous Mutations occurr randomly (Luria-Delbruck Mutations occurr randomly (Luria-Delbruck
experiment – fluctuation test, 1943)experiment – fluctuation test, 1943)
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Point mutationPoint mutation
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Insertion mutationsInsertion mutations
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DeletionDeletion
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MutantsMutants
Auxotrophs: Biochemically different Auxotrophs: Biochemically different from the parent (prototroph)from the parent (prototroph)
Resistant: Antimicrobial resistanceResistant: Antimicrobial resistance
Spontaneous mutations approx. 1 in 1 Spontaneous mutations approx. 1 in 1 millionmillion
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MutagenesMutagenes
UV-light (TT-UV-light (TT-dimers dimers formationsformations Mutations, Mutations, replication replication errors)errors)
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Chemicals llike:Urea, nitrous acide, Chemicals llike:Urea, nitrous acide, benzopyrene, etc...benzopyrene, etc...