gene expression

Bacterial Gene Expression


Operon- a group of genes that can be turned off and on

  • Genes- code for related enzyme in the pathway

  • Promoter- RNA polymerase attaches here

  • Operator- the on/off switch

    • Repressible- usually on but can be turned off

    • Inducible- usually off but can be turned on

Regulatory gene- produces a repressor protein that binds to operator to block transcription 

Examples:

Lac operon

  • Inducible 

  • Controls the synthesis of lactase



















Trp operon

  • Repressible

  • Controls the synthesis of tryptophan














Eukaryotic Gene Regulation

  • Regulated at many levels

    • Chromatid level

    • Transcription level

    • ?

    • Translation level

  • Involves epigenetic changes 

  • Different gene expressions leads to different type of cells


Chromatin structure (Eukaryotic Gene Regulation at Chromatid level)

  • Eukaryotic DNA wraps around proteins known as histone to form nucleosomes which forms chromatin 

  • Histones can be chemically modified

    • Chromatin remodeling

      • Histone Acetylation- acetyl group is added to histones which loosens DNA for transcription

      • DNA methylation- adds methyl group to DNA which inhibits transcription 


Transcription initiation (Eukaryotic Gene Regulation at Transcription level)

  • Transcription factor binds to control elements which are non coding DNA segments that regulates gene expression

    • 2 types of control elements

      • Enhancers - increase expression which activators binds to it

      • Silencer- reduce expression when repressor binds to it


Take notes of DNA bending proteins and mediator

Proteins which forms the Pre-initiation complex


RNAP I produces rRNA (highest in the nucleus)

RNAP II produces mRNA/snRNA

RNAP III produces tRNA



















Alternative splicing of pre-mRNA (Eukaryotic Gene Regulation at Translation level)

  • A single gene can code for more than 1 protein


RNA interference (RNAi) (Eukaryotic Gene Regulation at Translation level)

  • Translation can be inhibited by microRNA (miRNA), a type of noncoding RNA that matches the target mRNA

  • Small interfering RNA (siRNA) is artificially created to silence gene