The biochemistry aspect · Bacteria can grow in a E coli membrane minimum medium(N c H Converted into lts) ose in glycolytic Different carbon sources B-Galactosidase require a unique set of CH, OH Glucose Metabolized metabolizing enzymes a glycolytic two enzymes are required Permease proteins (transpart lactose from for lactose metabolism medium into E coli) lactose Allolactose B-galactosidase induces lactose permease synthesis in E coli in · Galactose epimerase poH B-Galactosidase lactose growth medium
The biochemistry aspect • Bacteria can grow in a minimum medium (N. C. salts) • Different carbon sources require a unique set of metabolizing enzymes • two enzymes are required for lactose metabolism: -galactosidase lactose permease • Galactose epimerase
Diauxic growth of E coli on a mixture of lactose glucose Copyright o The McGraw-Hill Companies, Perm ission required for reproduction or display Lactose used Glucose used 6 8 Figure 7.1 Time(h)
Diauxic growth of E. coli on a mixture of lactose + glucose
If E coli presented with glucose lactose,use mainly glucose until gone, then use lactose act ose 阝- galactosidase CH2OH CH2OH O、OH H O OH Glucose Galact ose OH lactose mucose epImerase lactose g ly coly sis
O OH CH2OH O OH CH2OH O HO HO OH OH galactose glucose lactose lac t ose Glucose Galact ose ep im erase g ly co ly sis -galactosidase If E.coli presented with glucose & lactose, use mainly glucose until gone, then use lactose
Lac Operon Repression No lactose; repression Op perator lacz Promoter mRNA Repressor monomer Tetramer lactose: derepress Transcription Inducer B-galactosidas Permease Transacetylase Fig. 7.3
Lac Operon: Repression Fig. 7.3
Regulatory mechanisms negative regulation负调控 repression 阻遏 negative induction regulation负控诱导 negative repression regulation负控阻遏 positive regulation.正调控: inductor诱导 - positive induction regulation正控诱导 positive repression regulation正控阻遏
Regulatory mechanisms • negative regulation负调控: repression阻遏 – negative induction regulation负控诱导 – negative repression regulation负控阻遏 • positive regulation正调控: inductor诱导 – positive induction regulation正控诱导 – positive repression regulation正控阻遏