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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...