Gene expression in prokaryotes


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Gene expression in prokaryotes

  1. 1. Gene expression in prokaryotes
  2. 2.  Genetic expression is the process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA  Non-protein coding genes (e.g. rRNA genes, tRNA genes) are transcribed, but not translated into protein
  3. 3.  Group of organisms lacking a cell nucleus or any other membrane-bound organelles.  Differ from the eukaryotes, which have a cell nucleus  Mode of division is binary fission  Prokaryotes exhibit efficient genetic mechanisms to respond to environmental conditions
  4. 4. Rod-Shaped Bacterium, Escherichia coli dividing by binary fission Rod-Shaped Bacterium, hemorrhagic E. coli, strain
  5. 5. * * * * * Type B
  6. 6.  Inducible gene − Regulated by inducer/activator  Constitutive gene − Not subjected to regulation
  7. 7.  Control at the level of transcription  Induction - the production of a specific enzyme/s in response to the presence of a substrate  Repression - the cessation of production of a specific enzyme/s in response to an increased level of a substrate
  8. 8.  All of the genes which encode the enzymes necessary for the pathway are found next to each other on the E. coli chromosome  A single mRNA carries information for multiple proteins  This type of mRNA is called a polycistronic mRNA and is totally unique to prokaryotes
  9. 9.  An operon model is a self-regulating series of genes found on DNA that work in concert  It includes a special segment of genes that are regulators of the protein synthesis, but do not code for protein, called the promoter and operator regions  Lactose (Lac), Tryptophan (Trp), L-Arabinose (Ara)
  10. 10.  Inducible system  Three genes part of an operon that code for three separate enzymes  Needed for the breakdown of lactose, a simple sugar
  11. 11. Lac I Promoter gene Operator gene Lac Z Lac Y Lac A RNA polymerase Repressor tetramer R Translation & Transcription Inactive repressor Desired product
  12. 12. Lac I Promoter gene Operator gene Lac Z Lac Y Lac A R Translation & Transcription RNA polymerase No Gene Expressio n
  13. 13. Lac I Promoter gene Operator gene Lac Z Lac Y Lac A mRNA R R RR Lactose absentRepressor molecules Repressor tetramer No Gene Expressio n RNA polymerase
  14. 14. Lac I Promoter gene Operator gene Lac Z Lac Y Lac A mRNA R R RR RNA polymerase mRNA Thiogalact oside transacetyl ase Permeas e β- galactosidase Inducer Inactive repressor R Lactose/ Isopropyl Thiogalactosid e (IPTG) present
  15. 15. If there occurs no glucose metabolism
  16. 16. Lac I Promoter gene Operator gene Lac Z Lac Y Lac A cAMP ↑↑↑ Glucose pool gets depleted due to metabolism CAP-cAMP complex formed cAMP RNA polymerase mRNA β-galactosidase Permease Thiogalactoside transacetylase If there occurs glucose metabolism R IR I
  17. 17. Trp Operon Model Trp A Trp C Trp B Trp LP/O Trp E Trp D
  18. 18. Tryptoph an synthetas e (B protein) Tryptopha n synthetase (A protein) Anthranil ate synthetas e Anthranil ate synthetas e Glycerol- phosphate synthetase
  19. 19. 1. L-arabinose operon model 2. Controlled by a dual positive and negative system 3. 3 structural genes: araB, araA, and araD 4. Encode the metabolic enzymes for breaking down arabinose for further metabolism via the HMP Shunt pathway