Biology
Genetics
12th
7.4 Gene Expression
Genes can be turned on/off according to conditions in the cellular environment.
Genes that are functionally related to one another are grouped into clusters called operons.
Cluster of 3 genes involved in lactose metabolism.
Consist of these genes plus:
Promoter - site where transcription starts.
Operator - regulates transcription.
Repressor - protein (lacI or lac repressor) that turns off genes based on lactose concentration, always produced
Low Lactose
High Lactose
binds to operator so that RNA polymerase cannot bind to promotor
Lactose acts as an inducer (triggers gene expression). Binds repressor changing shape so it can’t bind to operator.
No transcription, no proteins produced.
Transcription proceeds, proteins produced.
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