Biology The Lac Operon Flashcards

Operons

• Composed of adjacent genes transcribed as polycistronic mRNA.
• Coordinately regulated with associated regulatory sequences (promoter, operator).
• Primarily found in bacteria and archaea.

Lactose (lac) Operon

• Inducible operon with genes lacZ, lacY, and lacA, allowing E. coli to utilize lactose for energy.
• Repressed by lac repressor protein, which binds to the lac operator sequence.
• Activated by CAP-cAMP complex, enhancing transcription when lactose is present and glucose is absent.

Inducible Operon System

• Not expressed under certain environmental conditions but activated under alternative conditions.
• Activation occurs when lactose is present, and glucose is absent.

Lactose

• A disaccharide made of glucose and galactose linked by β-galactoside bond.

lac+ and lac- Phenotypes

• lac+ phenotype: Bacteria that can grow on lactose as the sole sugar source.
• lac- phenotype: Bacteria that cannot grow on lactose-containing media due to inability to import or metabolize lactose.

Allolactose

• A modified form of lactose that binds to the lac repressor protein.
• Induces a conformational change, reducing the repressor's ability to bind DNA.

Components of lac Operon

• Composed of a regulatory region and structural region.

Regulatory Region of lac Operon

• Contains:
  • Promoter for RNA polymerase binding.
  • Operator sequence for lac repressor binding.
  • CAP-cAMP binding site for transcription regulation.

Structural Genes of lac Operon

• lacZ: Encodes β-galactosidase, cleaving lactose into glucose and galactose.
• lacY: Encodes permease, facilitating lactose entry into the cell.
• lacA: Encodes transacetylase, involved in lactose metabolism.

Polycistronic mRNA

• Transcript containing all genes from the operon in a single mRNA molecule.

lacI

• Regulatory gene separate from lac operon, with its own promoter ensuring constant expression.

CAP-cAMP Complex

• A molecular complex that binds DNA, enhancing RNA polymerase's ability to initiate transcription of lac operon genes.

Catabolite Repression

• Presence of glucose represses genes for alternative carbon sources, such as lactose.
• Mechanism whereby glucose prevents transcription of lac operon genes.

Explore the concepts of the Lac operon in this set of flashcards. Learn about operons, their functions, and the role of lactose and regulatory sequences in gene expression. Ideal for students studying molecular biology and genetics.