28 public questions tagged with this topic.
The lac operon codes for enzymes that help digest lactose and is regulated by a repressor. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
The repressor protein binds to the operator region in the lac operon to block transcription in the absence of lactose. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Glucose represents most energetically efficient carbon source giving maximal ATP per bond and direct entry into glycolysis via phosphotransferase system without induction cost. Bacteria evolved catabolite repression as global control suppressing alternative substrate utilization when glucose present to conserve resources. In Escherichia coli mechanism involves drop in second messenger cAMP due to inhibition of adenylate cyclase CyaA by dephosphorylated EIIA-Glc during glucose transport and prevention of active CRP-cAMP complex formation that binds conserved DNA sequence upstream of lac, araBAD
Ref: Prescott's Microbiology, 11th ed., Chapter 6: Catabolite Repression and Glucose Preference in Bacteria.
The lac operon is an inducible operon that is activated in the presence of lactose to allow lactose metabolism.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
An inducible operon, like the lac operon, is normally off but can be activated by an inducer (e.g., lactose).
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
The lac operon is regulated by a repressor protein, which prevents transcription in the absence of lactose.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
The lac operon is activated in the presence of lactose, which inactivates the repressor and allows transcription.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
The repressor protein binds to the operator region in the lac operon to block transcription in the absence of lactose.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
The lac operon is not always active; it is only activated in the presence of lactose.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
lacA encodes beta-galactoside transacetylase, 203-amino-acid enzyme transferring acetyl group from acetyl-CoA donor to C6 hydroxyl acceptor of thiogalactosides and non-metabolizable lactose analogs. Crystallographic analysis reveals left-handed beta-helix fold assembled as trimer with active sites at subunit interfaces. Physiological role appears detoxification rather than primary catabolism: acetylation prevents accumulation of disulfide-forming thiogalactosides or other potentially toxic beta-galactosides that could irreversibly modify cellular proteins or glutathione, promoting their efflux
Ref: ResearchGate Lac operon GeneAct – lacA thiogalactoside transacetylase involved in cellular detoxification not catabolism.
lacY gene product is lactose permease LacY, 417-residue member of major facilitator superfamily transporter folded into twelve transmembrane alpha helices forming central hydrophilic cavity accessible alternately outward and inward during cycle. It operates as galactoside-proton symporter driven entirely by proton motive force, accumulating lactose against concentration gradient for metabolic use. Protein functionality is distinct from soluble beta-galactosidase encoded by lacZ and transacetylase LacA. By concentrating intracellular beta-galactosides, LacY enables efficient generation of allol
Ref: ScienceDirect Lactose Permease overview – LacY transmembrane symporter concentrates β-galactosides for hydrolysis and induction.
CAP, also called CRP, binds as homodimer to 22-base pair inverted repeat containing TGTGA-N6-TCACA consensus motif located upstream of lac promoter, typically centered at position -61.5. When glucose scarce, adenylate cyclase synthesizes second messenger cAMP that binds N-terminal effector domains of CAP, allosterically enabling C-terminal helix-turn-helix domains to specifically recognize major groove sequences. Dimer introduces approximately ninety-degree bend in DNA, contacts alpha-carboxy-terminal domain of RNA polymerase via activating region 1, stabilizes closed promoter complex, and acc
Ref: NCBI Bookshelf – Sigma; J Bacteriol 1997: CAP-cAMP binds 61.5 bp upstream lac promoter, Type I activation.
