Nitogen Fixing, LAB, Enzyme Induction

• inducible enzymes


  An enzyme whose transcription can be stimulated by an abundance of its substrate (as opposed to repressible enzyme). Usually in catabolism.
• repressible enzymes


  normally produced by the cell but its synthesis is turned off when it is not needed / enzyme synthesis is repressed if the product is present (anabolism)
• Operon


  A unit of genetic function common in bacteria and phages, consisting of coordinately regulated (by a operator) clusters of genes with related functions // A set of genes expressed (transcribed) as part of the same mRNA molecule (same transcription unit) are said to form an operon
• The lac operon in E. coli

  codes for proteins needed to transport lactose into the cell and break it down to glucose and galactose
• operon activated

  presence of lactose (and low levels of glucose)
• When the operon is activated

  B galactosidase is synthesized following induction of lac operon
• in order for Bacteria to ferment lactose they need two enzymes

  lactose permease & B galactosidase
• lactose permease (lacY)


  transports lactose across cell membrane
• B-galactosidase (lacZ)


  hydrolyzes disaccharide lactose into monosaccharides glucose and galactose
• Bacteria that can make lactose permease and B galactosidase are


  active lactose fermenters
• ONPG


  If the lac operon has been induced and create B galactosidase ONPG measures its activity. ONPG hydrolyzes in B galactosidases presence into galactose and o-nitrophenol (ONP) which appears yellow.
• ONP is indicator used to show

  presence of B-galactosidase
• two types of transcriptional controls regulate Lac operon

  positive & negative
• positive regulation of the Lac operon by CAP occurs when cAMP binds to CAP, activating it to bind to the Lac operon and promote gene expression. This activation is favored when glucose is scarce, as low glucose levels lead to higher cAMP levels, whereas high glucose inhibits cAMP production and CAP activation.
• negative regulation DNA binding form of a protein works to turn a gene off.

  Proteins work to inhibit binding of RNA polymerase to the operon
• diauxic growth curve


  - cells grown on a mixture of glucose and lactose

  - lag in growth occurs when glucose is gone and cells must make new enzymes to use lactose
• nitrogen-fixing bacteria


  bacteria that convert atmospheric nitrogen into ammonia
• Biological process that converts N2 in the atmosphere into NH3
• NH3 is then assimilated into amino acids and proteins
• Some are free living in soil


  (independent of other organisms) Azotobacter, Clostridium, Cyanobacteria spp
• Some are symbiotic (within characteristic nodules in roots of leguminous plants) Rhizobium, Frankia spp
• fixed nitrogen in the soil
• Azotobacter


  nitrogenase enzyme responsible for nitrogen fixation is anaerobic
• Rhizobium live

  endosymbiotically with leguminous plants
• endosymbiotic


  symbiosis in which one of the symbiotic organisms lives inside the other.
• leguminous plants


  clover, alfalfa, peas, peanuts, and soybeans
• Toluene 


  makes the membrane of E. coli bacteria cells easier to cross (cell membrane more permeable).
• Lac repressor protein responsible for inhibiting expression of Lac operon
• If lactose is present allolactose is an isomer that binds to the Lac repressor protein and removes it
• + glucose / + lactose = activator protein (CAP) and repressor protein (lac repressor) arent bound to operon = operon expression is off
• If cAMP is low its because a product of glucose breakdown inhibits enzyme adenylate cyclase preventing conversion of ATP into cAMP
• + glucose / - lactose = activator protein not bound to operon / repressor bound / operon expression = off
• (-) glucose / - lactose activator protein is bound to operon, repressor protein is bound = operon expression is off
• (-) glucose / + lactose = activator protein CAP is bound, Lac repressor protein isnt bound, operon expression is on
• What is lactic acid bacteria?

  group of bacteria that produce lactic acid as the major end product of carbohydrate fermentation
• What are the common genera for LAB?

  Streptococcus, Lactobacillus, Enterococcus, Lactococcus, Leuconostoc
• what are the characteristics of LAB bacteria?

  gram positive group of cocci or rods, non-respiring, non spore forming, non-motile, catalase negative
• What is lactic acid fermentation?

  anaerobic fermentation reaction which can be categorized in two ways: homolactic fermentation, heterolactic fermentation
• Homolactic fermentation: from one glucose molecule to two molecules of lactic acid

  In Glucose Durham Tubes: + for sugar fermentation / + for gas production
• Heterolactic fermentation: one glucose molecule is converted into CO2, ethanol, and lactic acid

  In Glucose Durham Tubes: + for sugar fermentation / - for gas production