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Terms in this set (17)

i) In Bacteria genes form together in a operon: group of two or more genes under the transcriptional control of a single promoter. An operon encodes a polycitronic RNA - RNA that contains the sequences for two or more genes.
(1) Operons occur in bacteria because it provides the advantage of controlling all the genes involved in a common functional goal; the expression of the genes occurs as a single unit (Ex: the use of one light switch for multiple lights, instead of a single light switch for each light).
ii) For transcription to occur an operon is flanked by a promoter - that signals the beginning of transcription - and a terminator - that specifies the end of transcription (two or more genes are between these two = operon).
iii) Two distinctive transcriptional genes are present in lactose utilization and transcriptional regulation
(1) Lac operon: contains a CAP site, promoter (lac P); operator site (lac O); three structural genes, LacZ, lacY, and lacA; and a terminator.
(a) LacZ encodes the enzyme B-glactosidase (cleaves lactose into galactose and glucose). Also converts lactose into allallolactose, which acts as a effector molecule that regulates the lac Operon.
(b) LacY gene encodes lactose permease, a membrane protein required for the active transport of lactose into the cytoplasm of the bacterium.
(c) LacA gene encodes glactoside transacetylase, an enzyme that covalently modifies lactose and lactose analogs. Which may prevent toxic buildup within the bacterial cytoplasm.
(d) CAP site - short DNA segments that function in gene regulation - CAP site is recognized by an activator protein called the Catabolic Activator Protein.
(e) Operator site - short segment of DNA sequence that function in gene regulation - is a sequence of bases that provides a binding site for a repressor protein.
(2) Second transcriptional unit involved in genetic regulation is the lacI gene (not apart of lac operon)
(a) Is constitutively expressed at low levels, has it's own promoter (i). The lacI encodes lac repressor - protein important for regulation of lac operon.
(i) Functions as homotetramere (four sub-units)
(ii) Only small amounts needed to repress the lac operon