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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) Transcription 5’-3’ direction Any strand of DNA can be transcribed No need for helicases, topoisomerases, primers RNA polymerase: 4 chains 2alpha, beta, Beta’ Promoter is recognised by the factor sigma some cases termination rho dependent factors, which are helicases Rho utilisation site 80-100 bp upstream of actual terminator In E. Coli other factors: tau, nus In In bacteria ribosomes 70 s = 50 S and 30 S 50 S subunits: 23 S and 5 S RNA molecules 30 S subunits: 16 S RNA and 21 polypeptides rRNA binds to m-RNA at spesific sequences: Shine-Dalgerno sequence (RBS) partly complementary to the 3’ end of 16 S RNA tRNA Secretion of the proteins Many proteins exert their functions on the cell surface or in extracellular environement they should across the cytoplasmic membrane GSP Sec dependent pathway Proteins utlising GSP have a specific sequence at their N termini, which is cleaved during the transport In Gram positive bacteria GSP is sufficient but ın Gram negative bacteria Proteins reach only to the periplasmic space Gram negatives have addional mechanism: Sec dependent and Sec independent Sec dependent systems Type II secretion system: A multiprotein complex transports proteins from the periplasmic space to the outside Type V secretion system: The proteins have an additional sequence at the C terminus, forming pores in the outer membrane (aototransporters) Sec independent systems Types I, III and IV Repair systems Proof-reading Miss-match repair: Methyle directed missmatch repair Excision repair:uvrA, B and C endonucleases Post-replication (recombination) repair: SOS repair:ssDNA stimulates rec A Rec A downregulates lex A whic repress SOS genes (18 genes) Error prone DNA repairing system MUTATION and VARIATION BActerial populations are not homgeneous Mutations occurr randomly (Luria-Delbruck experiment – fluctuation test, 1943) Point mutation Insertion mutations Deletion Mutants Auxotrophs: Biochemically different from the parent (prototroph) Resistant: Antimicrobial Spontaneous million resistance mutations approx. 1 in 1 Mutagenes UV-light (TT- dimers formations Mutations, replication errors) Chemicals llike:Urea, nitrous acide, benzopyrene, etc...