genetic organisation. in prokaryotes transcrition and translation occurs in same compartment...

Genetic OrganisationGenetic Organisation

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)

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

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

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

tRNAtRNA

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

In Gram positive bacteria GSP is sufficientIn Gram positive bacteria GSP is sufficientbut ın Gram negative bacteriabut ın Gram negative bacteria

Proteins reach only to the periplasmic spaceProteins reach only to the periplasmic space

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)

Sec independent systemsSec independent systems Types I, III and IVTypes I, III and IV

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

Post-replication Post-replication (recombination) (recombination) repair:repair:

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

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)

Point mutationPoint mutation

Insertion mutationsInsertion mutations

DeletionDeletion

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

MutagenesMutagenes

UV-light (TT-UV-light (TT-dimers dimers formationsformations Mutations, Mutations, replication replication errors)errors)

Chemicals llike:Urea, nitrous acide, Chemicals llike:Urea, nitrous acide, benzopyrene, etc...benzopyrene, etc...