Study Guide Exam #3 Study Guide: Chapters 11- Biology M01

3. What are the components of an operon?

-Promoter: RNA polymerase attaches here; a promotor signals the start of the operon and the location where transciption begins. -Operator: Regulatory protein binds here; The operator controls transcription of structural genes. -Structural genes: One or several metabolic genes; Transcribed as a unit. Prokaryotes uses operons.

gene expression

In gene expression, a gene is turned on and transcribed into RNA.

Gene regulation in Bacteria: An operon:

An operon is a cluster of genes with related functions together with their promoter and other dnA sequences that control their transcription. For example, the lac operon allows E. coli to produce enzymes for lactose use only when the sugar is present.

Gene regulation

Certain genes are turned on and off in the process of gene regulation.

cell signaling

In Cell Signaling • In a multicellular organism, gene regulation can cross cell boundaries. • A cell can produce and secrete chemicals, such as hormones, that affect gene regulation in another cell.

silencers

In the Initiation of Transcription • Repressor proteins called silencers - bind to DNA and - inhibit the start of transcription.

activators

In the Initiation of Transcription: Activators - are more typically used by eukaryotes than silencers and - turn genes on by binding to DNA.

6. In eukaryotic cells, how is regulation at the level of initiation of TRANSLATION controlled?

The Initiation of Translation • The process of translation offers additional opportunities for regulation by regulatory molecules. -After an mRNA is produced in its final form, its "lifetime" can be highly variable, from hours to weeks to months. Controlling the timing of mRNA break- down provides another opportunity for regulation. But all mRNAs are eventually broken down and their parts recycled. -Another control mechanism operating after translation is the selective breakdown of proteins. Some proteins that trigger metabolic changes in cells are broken down within a few minutes or hours. This regulation allows a cell to adjust the kinds and amounts of its proteins in response to changes in its environment.

2. What is the responsible for different cell types?

The great differences among cells in an organism must result from the selective expression of genes. The various types of cells in a multicellular organism owe their distinctive- ness to different combinations of genes being turned on and off via gene regulation in each cell type.

4. Know how the lac operon works and how it is regulated.

The lac operon is an inducible operon that utilizes lactose as an energy source and is activated when glucose is low and lactose is present.

The lac operon uses

The lac operon uses - a promoter, a control sequence where the transcription enzyme attaches and initiates transcription, - an operator, a DNA segment that acts as a switch that is turned on or off, and - a repressor, which binds to the operator and physically blocks the attachment of RNA polymerase and transcription.

5. In eukaryotic cells, how is regulation at the level of initiation of TRANSCRIPTION controlled?

a model for turning on a eukaryotic gene. A large assembly of transcription factors (proteins shown in purple) and several control sequences in the dnA are involved in initiating the transcription of a eukaryotic gene. The initiation of transcription (whether transcription starts or not) is the most important stage for regulating gene expression. In both prokaryotes and eukaryotes, regulatory proteins bind to DNA and turn the transcription of genes on and off. Unlike prokaryotic genes, however, most eukaryotic genes are not grouped into operons. Instead, each eukaryotic gene usually has its own promoter and other control sequences. Transcriptional regulation in eukaryotes is complex, typically involving many proteins (collectively called transcription factors; shown in purple in the figure) acting in concert to bind to DNA sequences called enhancers (yellow) and to the promoter (green). The DNA-protein assembly promotes the binding of RNA polymerase (orange) to the promoter. Genes coding for related enzymes, such as those in a metabolic pathway, may share a specific kind of enhancer (or collection of enhancers), allowing these genes to be activated at the same time. Not shown in the figure are repressor proteins, which may bind to DNA sequences called silencers, inhibiting the start of transcription.

7. What are DNA microarrays used for?

• A DNA microarray allows visualization of gene expression. • The pattern of glowing spots enables the researcher to determine which genes were being transcribed in the starting cells. • Researchers can thus learn which genes are active - in different tissues or - in tissues from individuals in different states of health.

operon

• An operon includes - a cluster of genes with related functions and - the control sequences that turn the genes on or off. • The bacterium E. coli uses the lac operon to coordinate the expression of genes that produce enzymes used to break down lactose in the bacterium's environment.

X-chromosome inactivation

• Cells may use DNA packing for long-term inactivation of genes. • X chromosome inactivation - takes place early in embryonic development, - occurs in female mammals, and - is when one of the two X chromosomes in each cell is inactivated at random.

Cellular differentiation

• In cellular differentiation, cells become specialized in - structure and - function.

homeotic genes

• Master control genes called homeotic genes regulate groups of other genes that determine what body parts will develop in which locations. • Mutations in homeotic genes can produce bizarre effects.