Gene Regulation. Regulation in Prokaryotes Gene Expression = gene to protein processing that...

Gene Regulation

Regulation in Prokaryotes

• Gene Expression = gene to protein processing that functions within cells.

• Regulation = We are talking about controlling gene transcription and translation.

• Produce proteins where and when they are needed !!

The Operon (Prokaryotes Only*)

• Operon - group of genes that operate together.

• Components:

–Regulator gene

–Promoter region

–Operator gene

–Structural genes

Promoter and Operator

The promoter is where RNA polymerase binds to begin transcription.

The operator is where repressor proteins bind to stop transcription

When the repressor proteins are bound to the operator, RNA polymerase is unable to bind to the promoter.

-Repressor Proteins bound to operator = RNA polymerase cannot bind = gene is “off” = no transcription-Repressor proteins not bound to the operator = RNA polymerase can bind = gene is “on” = transcription

• All genes must be transcribed and translated

• RNA polymerase will move from left to right

• Promoter region is not itself a gene; rather is

the place where polymerase will attach...

Components of an Operon

RG P Op SG1 SG2 SG3

Regulator Gene

Promoter Region

Operator Gene

Structural Genes 1,2&3

Example of Regulation in Prokaryotes

• Earliest research was done in E. coli• E. coli is single celled bacterium;

changes functioning in relation to environmental cues.

http://njaes.rutgers.edu/seafoodsafety/sssan.html

http://science.howstuffworks.com/cellular-microscopic-biology/dna2.htm

The lac operon

• E. coli can use lactose as a food source by breaking down lactose into simple sugars.

• Specific proteins are needed to break down lactose into these sugars.

• E. coli only produces these proteins in the presence of lactose.

• How does the E. coli cell control when to produce these lactose proteins?

Regulation of the lac operon

• Figure 12-23– No lactose = the lac repressor protein is

continuously bound to the operator = RNA polymerase cannot bind = no transcription

– In the presence of lactose:• The lac repressor protein has a binding site for

lactose• When lactose is taken in by the cell, it binds to the

lac repressor protein and removes it from the operator.

• No repressor protein = RNA polymerase can bind to the promoter = gene is turned “on” = transcription

Other Forms of Regulation

• Repressor proteins are not the only way to regulate genes in prokaryotes

• Regulation can occur in:– The rate of transcription– Protein synthesis

Eukaryotic Gene Regulation

• Operons are generally not found in eukaryotes.

• Eukaryotic organisms have more complex ways of regulating their genes.

• Why is gene regulation more complex in eukaryotes?

Gene Regulation in Eukaryotes

• Every cell in our bodies contains all of our DNA (genome).

• If every cell contains every piece of DNA, why do we have different types of cells?– Different genes for each type of cell are

transcribed, producing different types of proteins.

What ways can cells regulate gene expression in eukaryotes?

TATA Box

• TATA Box – sequence of nucleotides that are found between the promoter and the start of transcription.– Marks a point just before transcription to help

position RNA polymerase.

Enhancer Sequences

-Enhancer Sequences- sequences of DNA located before the start of transcription

-Many different types of proteins can bind to different enhancer sequences to affect transcription:

-Opening up tightly-packed chromatin

-Attract RNA polymerase

Gene Regulation and Development

• How does a fertilized egg become a multi-cellular adult?

• During embryonic development, cells differentiate into different types (muscle cells, nerve cells, etc).

• What causes this differentiation of cells during development?

Hox genes

• Series of genes that control differentiation of cells and tissues in an embryo.

• What would happen if a mutation were to occur in one of these genes?– A mutation in the hox genes could completely

change the cell types that normally develop.• Example: Drosophila- antennae can be replaced

by legs

• Answer Questions p. 326 #1-5

• Due Monday, 2/28/11

Evolution Connection

• Pax 6: gene that controls eye growth in fruit flies– Similar genes that control eye growth exist in

mammals such as mice.– When a copy of the mice gene was inserted

into the “knee” DNA of a fruit fly embryo, the fly grew an eye on its leg.

Many genes that control development in separate species may have had a common ancestor.

Copyright Pearson Prentice Hall

13-2 Manipulating DNA


The Tools of Molecular BiologyHow do scientists make changes to DNA?

The Tools of Molecular Biology



Scientists use different techniques to:• extract DNA from cells• cut DNA into smaller pieces• identify the sequence of bases in a DNA molecule• make unlimited copies of DNA



In genetic engineering, biologists make changes in the DNA code of a living organism.



DNA ExtractionDNA can be extracted from most cells by a simple chemical procedure.

The cells are opened and the DNA is separated from the other cell parts.



Cutting DNA Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using restriction enzymes.

Which type of molecule is an enzyme?



Each restriction enzyme cuts DNA at a specific sequence of nucleotides.

Recognition sequences

DNA sequence

Restriction enzyme EcoR I cuts the DNA into fragments

Sticky end



Separating DNA In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel.



DNA plus restriction enzyme

Mixture of DNA fragments

Gel

Power source

Gel Electrophoresis

Longer fragments

Shorter fragments



First, restriction enzymes cut DNA into fragments.

The DNA fragments are poured into wells on a gel.

DNA plus restriction enzyme

Mixture of DNA fragments

Gel

Gel Electrophoresis



An electric voltage is applied to the gel.

The smaller the DNA fragment, the faster and farther it will move across the gel.

Power source



Longer fragments

Shorter fragments

Gel Electrophoresis

Power source


Using the DNA Sequence

Making Copies Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes.

Small amounts of DNA can be multiplied making it easier to analyze.

Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone National Park.


Using the DNA Sequence

DNA heated to separate strands

PCR cyclesDNA copies

1 2 3 4 5 etc.1 2 4 8 16 etc.

Polymerase Chain Reaction (PCR)

DNA polymerase adds complementary strand

DNA fragment to be copied

Gene Regulation. Regulation in Prokaryotes Gene Expression = gene to protein processing that...

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