12-5 Gene Regulation

I. Gene Regulation: An Example

E. Coli (bacteria) gives a good example of how genes are able to regulate being expressed

Operon- a group of genes that operate (work) together E. Coli use lactose (milk sugar) as a food source To eat the lactose the genes to eat the sugar must be turned on Lac Operon- genes that allow E. coli to eat lactose

Repressor- turns off genes Operator- area of a chromosome in an operon that the repressor binds to when the operon is “turned off” Lac genes are turned off by the repressor Lac genes are turned on by the presence of lactose

Many genes are regulated by repressor proteins Some genes use proteins that speed up transcription. Sometimes regulation occurs at the level of protein synthesis.

Discuss w/ Partner: Pg. 310 fig. 12-23 When is the repressor protein bound to the operator? Can transcription occur when the repressor is bound to the operator? Why or why not? How does the presence of lactose help start transcription of the lac genes?

Answer: When is the repressor protein bound to the operator? When lactose is not present Can transcription occur when the repressor is bound to the operator? No Why or why not? The repressor protein blocks RNA polymerase from binding to the promoter How does the presence of lactose help start transcription of the lac genes? Lactose binds to the repressor protein, causing it to release from the operator site, and RNA polymerase can bind to the promter

II. Eukaryotic Gene Regulation

Operons are not found in eukaryotic organisms …..but… Most eukaryotic genes: are controlled individually have regulatory sequences that are much more complex than those of the lac operon.

TATA Box- a short region of DNA that helps start transcription Helps RNA polymerase bind to DNA

Discuss w/ Partner: Pg. 309 fig. 12-22 What codon sequence would you expect to find in the mRNA at the place where transcription starts? At the place where transcription ends? What kinds of molecules bind to the regulatory sites of genes? What is the action of these proteins on genes?

Answer What codon sequence would you expect to find in the mRNA at the place where transcription starts? AUG, the start codon At the place where transcription ends? Any one of the three stop codons- UAA,UAG, or UGA What kinds of molecules bind to the regulatory sites of genes? DNA –binding proteins What is the action of these proteins on genes? They turn genes off or on

III. Development and differentiation

Differentiation- as cells grow & divide they become specialized in structure and function with the help of hox genes Hox genes- control the differentiation of cells and tissues in the embryo

All hox genes are descended from the genes of common ancestors. Careful control of expression in hox genes is essential for normal development All hox genes are descended from the genes of common ancestors. Each color reflects genes on a chromosome that form similar structures in different species