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Gene RegulationBy: Morgan McFarland, Alicia Switlick, and Taylor Newcome

Prokaryotic Gene Regulation

VOCABULARY:

Operon- a group of genes that are regulated together. In prokaryotes, a group of adjacent genes that share a common operator and promoter and are transcribed into a single mRNA.  

Operator- short DNA region, adjacent to the promoter of a prokaryotic operon, that binds repressor proteins responsible for controlling the rate of transcription of the operon.

Prokaryotic Gene Regulation

Bacteria and other prokaryotes do not need to transcribe all of their genes at the same time.

Prokaryotes regulate their activities, by only using the genes that are necessary for the cell to function to conserve energy.

Example: it would be wasteful for a bacterium to produce enzymes that are needed to make a molecule that is readily available from it’s environment.

Prokaryotic Gene Regulation

By regulating gene expression, bacteria can respond to changes in their environment – it could be the presence or absence of nutrients.  

DNA- binding proteins in prokaryotes regulate genes by controlling transcription.

Some of these proteins help switch genes on, while other turn genes off.

How does an organism know when to turn a gene on or off? One of the keys to gene transcription in bacteria is the organization of genes in to Operons.

The genes in an operon (genes regulated together) usually have related functions.

Prokaryotic Gene Regulation: The Lac

Operon E. coli must be able to switch the lac genes on and

off:

Lactose is a compound made up of two simple sugars, galactose, and glucose. To use lactose for food, the bacterium must transport lactose across it’s cell membrane and then breake the bond between glucose and galactose.

These tasks are performed by proteins coded for by the genes of the lac operon. This means that if the bacterium grows in a medium where lactose is the only food source, it must transcribe these genes and produce these proteins.

Prokaryotic Gene Regulation: The Lac

Operon If it is grown on another food source, such as

glucose, it would have no need for these proteins.  

The bacterium usually “knows” when the products of the genes are needed.

When lactose is not there, the lac genes are turned off by proteins that bind to DNA and block transcription.

Prokaryotic Gene Regulation: Promoters and Operators.

Two regulatory regions are on one side of the operons three genes. The first promoter (P) which is a site where RNA-polymerase can bind to begin transcription.

The other region is called the operator (O) def. above.

The O site is where a DNA binding protein, known as the lac repressor can bind to DNA.

Prokaryotic Gene Regulation: The Lac Repressor Blocks Transcription

When a lac repressor binds to the O region, RNA polymerase cannot reach the lac genes to begin transcription. In effect, the binding of the repressor protein switches the operon “off” by preventing the transcription of it’s gene.

Prokaryotic Gene Regulation: Lactose Turns the Operon

“on” If the representing protein is always present, how can

the lac genes be switched on?

The lac repressor protien has a binding site for lactose.

When lactose is added to the medium, it diffuses into the cell and attaches to the lac repressor.

This changes the shape of the repressor protein that makes it fall off the operator

Now RNA merase can bind to the promoter and transcribe the genes of the operon; in the presence in lactose, the operon is automatically switched on.

Eukaryotic Gene Regulation

RNA interference – blocking gene expression by means of miRNA silencing complex

How are genes regulated in eukaryotic cells?

The general principles of gene regulation in prokaryotes also apply to eukaryotes, but there are some differences.

Most eukaryotic genes are controlled individually and have more complex regulatory sequence

Transcription is the process of binding DNA sequences in the regulatory region of eukaryotic genes, transcription factors control the expression of those genes. Cell specialization requires genetic specialization, yet all of the cells in a multi-cellular organism carry the same genetic code in their nucleus.

After the small interfering RNA molecules are produced by transcriptions, they fold into double-stranded hairpin-like loops. An enzyme called the “Dicer” cuts or dices these double-stranded loops into microDNA or miRNA , each about 20 base pairs long. The two strands of the loop separate. Next, one of the miRNA pieces attaches to a cluster of proteins to form what is known as a Silencing complex.

There are three major groups of RNA: mRNA, tRNA and, rRNA.

After it is created the silencing complex binds to and destroys any mRNA containing a sequences that is complementary to the miRNA

Blocking gene expression by means of a miRNA silencing complex is known as RNA interference.

Genetic Control of Development

Vocabulary: Differentiation- becoming specialized in structure and function

Homeotic Gene- regulates organs that develop in specific body parts

Homeobox genes- code for transcription factors that activate other genes that are important in cell development and differentiation

Hox Gene- a group of homeobox genes

Genetic Control of Development

- Regulating gene expression is especially important in shaping the way a multicultural organism (a mouse embryo)

- The transformation to a single celled zygote to a multicultural embryo is one of the most amazing processes

- Some things can affect the way a organisms adapts to its envrionmentExamples: Temperature, amount of air, and sunlight etc.

Genetic Control of Development

The genes an animal or species has helps determine the way its going to develop to its environment

Gene Regulation ReviewProkaryotic Gene Regulation:

To (1) CONSERVE energy and resources, prokaryotes regulate their activities, using only those genes necessary to function.

DNA-binding proteins in prokaryotes regulate genes by controlling (2)TRANSCRIPTION.

A (3) OPERON is a group of genes that are regulated together.

(4) LACTOSE is a compound made up of two simple sugars, galactose, and glucose.

To use lactose for food, the (5) BACTERIUM must transport lactose across it’s cell membrane and then break the bond between (6) GLUCOSE and (7)GALACTOSE.

Remarkably, the bacterium almost seems to (8) “KNOW” when the products of these genes are needed. When lactose is not present, the lac genes are turned off for proteins that bend to DNA and(9) BLOCK transcription.

Review Continued…(10) OPERATOR is a short DNA region, adjacent to the promoter of a prokaryotic operon, that binds repressor proteins responsible for controlling the rate of transcription.

When lactose is added to the medium, it diffuses into the cell and (11) ATTACHES to the lac repressor.

Eukaryotic Gene Regulation

Gene expression in eukaryotic cells can be regulated at a number of levels. One of the most critical is the level of  (12) TRANSCRIPTION

Gene regulation in eukaryotes is (13)MORE complex than in prokaryotes.

Complex gene regulation in eukaryotes is what makes (14)SPECIALIZATION possible.

After the two strands of the miRNA loop separate, one of the pieces attaches to a cluster of proteins to form what is known as a (15) SILENCING complex

Blocking gene expression by means of an miRNA silencing complex is know as(16) RNA interference

Review Continued…

Genetic Control of Development

(17)_DIFFERENTIATION___ is becoming specialized in structure and function

(18)___HOMEOTIC GENE___ regulates organs that develop in specific body parts

(19)____HOMEOBOX GENE_____ code for transcription factors that activate other genes that are important in cell development and differentiation

(20)____HOX GENE____ a group of homebox genes

regulating gene expression is (21)_ESPECIALLY__ important in shaping the way a multicultural organism