12-5 GENE REGULATION. I. GENE REGULATION: AN EXAMPLE.

12-5 GENE REGULATION

I. GENE REGULATION: AN EXAMPLE

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

2. Operon- a group of genes that operate (work) together

a) E. Coli use lactose (milk sugar) as a food source

b) To eat the lactose the genes to eat the sugar must be turned on

c) Lac Operon- genes that allow E. coli to eat lactose

3. Repressor- turns off genes4. Operator- area of a chromosome in an

operon that the repressor binds to when the operon is “turned off”

a) Lac genes are turned off by the repressor

b) Lac genes are turned on by the presence of lactose

5. Many genes are regulated by repressor proteins

6. Some genes use proteins that speed up transcription.

7. Sometimes regulation occurs at the level of protein synthesis.

Repressor

Discuss w/ Partner:

Pg. 310 fig. 12-231. When is the repressor protein bound

to the operator?2. Can transcription occur when the

repressor is bound to the operator?3. Why or why not?4. How does the presence of lactose

help start transcription of the lac genes?

Answer:

1. When is the repressor protein bound to the operator? When lactose is not present

2. Can transcription occur when the repressor is bound to the operator? No

3. Why or why not? The repressor protein blocks RNA polymerase from binding to the promoter

4. 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

1. Operons are not found in eukaryotic organisms …..but…

2. Most eukaryotic genes:a) are controlled individually b) have regulatory sequences

that are much more complex than those of the lac operon.

3. TATA Box- a short region of DNA that helps start transcription

4. Helps RNA polymerase bind to DNA

Discuss w/ Partner:

Pg. 309 fig. 12-221. What codon sequence would you

expect to find in the mRNA at the place where transcription starts?

2. At the place where transcription ends?3. What kinds of molecules bind to the

regulatory sites of genes?4. What is the action of these proteins on

genes?

Answer

1. What codon sequence would you expect to find in the mRNA at the place where transcription starts? AUG, the start codon

2. At the place where transcription ends? Any one of the three stop codons- UAA,UAG, or UGA

3. What kinds of molecules bind to the regulatory sites of genes? DNA –binding proteins

4. What is the action of these proteins on genes? They turn genes off or on

III. DEVELOPMENT AND DIFFERENTIATION

1. Differentiation- as cells grow & divide they become specialized in structure and function with the help of hox genes

2. Hox genes- control the differentiation of cells and tissues in the embryo

3. Careful control of expression in hox genes is essential for normal development

4. 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