KEY CONCEPT Gene expression is carefully regulated in both prokaryotic and eukaryotic cells. Chapter 11 – Gene Expression

Genome – the complete genetic material contained in an individual or organism. Genome

Cells use information in genes to build several thousands of proteins. Control of Gene Expression But not all proteins are required by the cell at any one time. By regulating gene expression, cells are able to control when each protein is made. By controlling gene expression, organisms can conserve resources and produce only those proteins that are needed.

Gene expression – activation or “turning on” of a gene that results in transcription and production of mRNA. Control of Gene Expression Most of the mRNA is translated into proteins. But cells do not always need to produce all of the proteins that they can. Mechanisms to control gene expression have evolved so that each protein is only produced when needed.

Prokaryotic cells turn genes on and off by controlling transcription. Structural Genes – genes that code for polypeptides Promoter – is a DNA segment that is recognized by RNA polymerase and allows a gene to be transcribed. Operator – a DNA segment that serves as an “on-off” switch for genes –It controls access of RNA polymerase to the promoter. Gene Expression in Prokaryotes

Prokaryotic cells turn genes on and off by controlling transcription. Operon – includes a promoter, an operator, and one or more structural genes that code for all the proteins needed to do a job. Gene Expression in Prokaryotes

The Operon in the “OFF” position. Repressor Protein – a protein that inhibits a gene from being expressed Regulator Genes – genes that code for repressor proteins. They are located away from the operator they affect Gene Expression in Prokaryotes

The Operon in the “ON” position. Inducer – a substance or molecule, which when present, initiates gene expression to occur. Gene Expression in Prokaryotes

The lac operon acts like a switch. –The lac operon is “off” when lactose is not present. –The lac operon is “on” when lactose is present. The lac operon

Importance of Gene Expression By regulating gene expression, cells are able to control when each protein is made. By controlling gene expression, organisms can conserve resources and produce only those proteins that are needed.

Read Page 220, Section ~ Gene Expression in Eukaryotes. Gene Expression in Eukaryotes

Much of the control of gene expression in eukaryotes takes place at the level of the individual chromosome. As in prokaryotes, RNA polymerase binds to the promoter.

Gene Expression in Eukaryotes In eukaryotic genes, there are two kinds of segments beyond the promoter. Introns – sections of a structural gene that are transcribed into mRNA but not translated into proteins. Exons – sections of a structural gene that are expressed and are both transcribed and translated.

Eukaryotes regulate gene expression at many points. Different sets of genes are expressed in different types of cells. Each gene has a unique combination of regulatory sequences. –Some transcription is controlled by regulatory DNA sequences (like a TATA box). Gene Expression in Eukaryotes

Some transcription is controlled by regulatory proteins. –Enhancers – proteins that speed up the rate of transcription. –Silencers – proteins that slow down the rate of transcription. Gene Expression in Eukaryotes

RNA processing is also an important part of gene regulation in eukaryotes. mRNA processing includes three major steps: 1.Introns are removed and exons are spliced together. 2.A cap is added. 3.A tail is added. Gene Expression in Eukaryotes

KEY CONCEPT The control of gene expression plays an important role in the growth of eukaryotes. Chapter 11 – Gene Expression

In eukaryotes, gene expression helps cells become specialized to perform different tasks. Gene Expression and Development When the expression of genes is altered (by mutations for example) abnormalities and even cancer can occur.

All multicellular organisms begin life as a single-celled zygote. Gene Expression and Development Although every cell in the developing zygote has all of the organism's genes, only a small number of the genes are expressed. Certain genes are turned on and off as different proteins are needed at different times during an organism’s life.

As organisms grow and develop, organs and tissues develop to produce a characteristic form. Cell differentiation – development of cells that have specialized functions Cell Differentiation Homeotic genes – regulatory genes that determine where certain anatomical structures (arms, legs, heart, etc.) will develop in an organism.