Regulation of Gene Expression
Differentiation and De-Differentiation of Cell Types According to a plant tissue culture experiment:
• Different cell types of a multi-cellular organism contain the same DNA. • Genes expressed in one tissue differ from those expressed in another tissue.
(The genetic functional units) Structural Genes (SG) Coding (Expressed) Transcribed to mRNA, rRNA, tRNA Promoter Constitutive genes Expressed at fixed rates Site of transcription initiation Terminator Site of transcription termination Regulated genes Affected by external factors Operator Site of repressor binding
Regulator Genes (RG) Non-coding (Not expressed)
Operon = Transcription Unit
= Regulator gene(s) + linked Structural gene(s) + Terminator
Structural gene of mRNA (ORF for DNA)
Protein coding gene
Open Reading Frame
? (Cistron or ORF for mRNA) ? The coding unit for one peptide chain ?
Start codon + n(3N) + Stop codon
Mono-cistronic mRNA (More common in eukaryotes)
Polycistronic Operons (e.g. Lactose Operon): Contain >1 protein coding gene (ORFs or cistrons)
RNA polymerase binding site
Repressor binding site
Poly-cistronic mRNA (More common in prokaryotes)
Regulation of Gene Expression Importance of regulating gene expression:
• In simple unicellular organisms: Environmental adaptation • In complex multi-cellular organisms: Tissue specialization
• Can be regulated at each step in the pathway
Which of these regulations is restricted to eukaryotes?
a. b. c. d. a. b. c. d.
2, 4 3, 6 2, 3 3, 5 exon intron gene allele
In RNA processing, ……….. sequences are removed.
Answers: c & b
 Transcriptional Control of Gene Expression
A. Transcriptional control by chromosomal proteins in eukaryotes Histone proteins + DNA Complexing Genes off (No…