bacteria

• Operon: a cluster of functionally related genes, which are under the control of the same promoter and operator, allowing for functionally related proteins to be synthesized together➔It includes a common promoter, an operator, and one or more structural genes that are controlled as a unitWhen the structural genes are transcribed, a polycistronic mRNA is produced
• importance of bact cell to decrease expression

  • conserve rss
  • utilise arg from surrounding
• Transformation


  uptake of naked, foreign DNA from the surrounding, resulting in a change of the bacterial cell’s genotype and phenotype
• transformation

  Fragments of foreign naked DNA in the surrounding medium are taken up by naturally competent bacterial cells via cell surface proteins. Foreign DNA is incorporated into host cell chromosome through homologous recombination

  
  

  Result: a recombinant cellIf different alleles of a gene were exchanged and the new allele is expressed ➔ permanent change in genotype & phenotype, cell is said to be transformed
• transduction

  process which bacterial DNA from one host cell is introduced into another bacterial host cell by a bacteriophage due to aberrations inthe phage reproductive cycle
• generalised transduction

  -phage infects bacterium by injecting viral genome into host cell-bacterial DNA is degraded into small fragments, one of which may be randomly packaged into a capsid head during spontaneous assembly of new viruses

  
  

  -upon lysis of the donor bacterium, the defective phage will infect a recipient bacterium by injecting the bacterial DNA from the donor bacterium into it

  
  

  -foreign bacterial DNA (from donor bacterium) can replace the homologous region in the recipient cell’s chromosome through homologous recombination, allowing exp of a diff allele from the donor bacterium
• specialised transduction


  -Temperate phage infects bact, inject viral genome into HC-viral DNA integrate bact chromo form prophage

  
  

  -viral dna improperly excised to incl adj segment of bact DNA and not entire phage DNA during induction event-phage-bact hybrid DNA packaged into capsid head during spon assem of new virus

  
  

  -Upon cell lysis, defective recomb phage infects recipient bact by injecting phage-bact hybrid DNA

  
  

  -New alleles from donor bact cell incorp into recipient bact cell genome by homo recomb or int of phage-bact hybrid DNA as defective phage enters lysogenic cycle
• conjugation


  Direct transfer of genetic material from one bacterial cell to another through a mating bridge between the two cells, via the transfer of F plasmid from an F+ donor to F– recipient cell
• 1. Sex pilus of F+ bact makes contact with a F- cell and retracts to bring 2 cells closer
  2. hollow pilus acts as a cytoplasmic mating bridge btwn 2 cells
  3. 1 of the 2 strands of the plasmid DNA nicked and transf from F+ cell to F- cell through mating bridge. The other strand is usedas a T for syn of a complementary strand thus forming a double-stranded plasmid in the donor cell
  4. ss F plasmid DNA circularizes in F - cell and is used as a T to syn a complementary strand in order to form ds plasmid DNA. The F- recipient cell is now a F+ cell
  5. Rep of plasmid occurs via rolling circle DNA rep
• binary fission

  dna rep begins at ori, where dna is unzipped by breaking H bonds btwn bases of each strand to form A REPLICATION BUBBLE. dna rep via SCR where each ORI strand serves as T to syn comple daughter strand via CBP. 2 newly formed ori move towards opp poles of cell AND ATTACH TO PM, cell elongates TO prep for division. dna is circular w no free ends, daughter dna MOLS is interlocked w completion of rep, topoisomerase cuts sep reseals THE 2 DNA MOLS, invag of PM and deposition of new CW eventually divides parent cell into 2 daughter cells