How can similar genes be expressed differently

Regulation of gene expression. Phillips, T. Regulation of transcription and gene expression in eukaryotes. Nature Education , 1 1 , Purves, W. Transcriptional regulation of gene expression. In Life: The science of biology 7th ed. Reece, J. Eukaryotic gene expression is regulated at many stages. In Campbell Biology 10th ed.

San Francisco, CA: Pearson. Improve this page Learn More. Skip to main content. Module Gene Expression. Search for:. Figure 3: Transcription repression near the promoter region. Molecules can interfere with RNA polymerase binding. An inactive repressor protein blue can become activated by another molecule red circle. This active repressor can bind to a region near the promoter called an operator yellow and thus interfere with RNA polymerase binding to the promoter, effectively preventing transcription.

For an example of how this works, imagine a bacterium with a surplus of amino acids that signal the turning "on" of some genes and the turning "off" of others.

In this particular example, cells might want to turn "on" genes for proteins that metabolize amino acids and turn "off" genes for proteins that synthesize amino acids. Some of these amino acids would bind to positive regulatory proteins called activators. This binding facilitates RNA polymerase activity and transcription of nearby genes. At the same time, however, other amino acids would bind to negative regulatory proteins called repressors , which in turn bind to regulatory sites in the DNA that effectively block RNA polymerase binding Figure 3.

The control of gene expression in eukaryotes is more complex than that in prokaryotes. In general, a greater number of regulatory proteins are involved, and regulatory binding sites may be located quite far from transcription promoter sites. Also, eukaryotic gene expression is usually regulated by a combination of several regulatory proteins acting together, which allows for greater flexibility in the control of gene expression.

Figure 4: The complexity of multiple regulators Transcriptional regulators can each have a different role. Combinations of one, two, or three regulators blue, green, and yellow shapes can affect transcription in different ways by differentially affecting a mediator complex orange , which is also composed of proteins. The effect is that the same gene can be transcribed in multiple ways, depending on the combination, presence, or absence of various transcriptional regulator proteins. As previously mentioned, enhancer sequences are DNA sequences that are bound by an activator protein, and they can be located thousands of base pairs away from a promoter, either upstream or downstream from a gene.

Activator protein binding is thought to cause DNA to loop out, bringing the activator protein into physical proximity with RNA polymerase and the other proteins in the complex that promote the initiation of transcription Figure 4. Different cell types express characteristic sets of transcriptional regulators.

In fact, as multicellular organisms develop, different sets of cells within these organisms turn specific combinations of regulators on and off. Such developmental patterns are responsible for the variety of cell types present in the mature organism Figure 5. Figure 5: Transcriptional regulators can determine cell types The wide variety of cell types in a single organism can depend on different transcription factor activity in each cell type.

Different transcription factors can turn on at different times during successive generations of cells. As cells mature and go through different stages arrows , transcription factors colored balls can act on gene expression and change the cell in different ways. This change affects the next generation of cells derived from that cell. In subsequent generations, it is the combination of different transcription factors that can ultimately determine cell type.

This page appears in the following eBook. Aa Aa Aa. Gene Expression. How Is Gene Expression Regulated? Figure 1: An overview of the flow of information from DNA to protein in a eukaryote. Figure 2: Modulation of transcription. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.

Can genes be turned on and off in cells? Chromatin Remodeling in Eukaryotes. RNA Functions. Citation: Ralston, A. Nature Education 1 1 How is it that your body with all of its specialized organs developed from a single cell?

Scientists are exploring how gene expression patterns and their timing regulate cell differentiation. Aa Aa Aa. Figure 1: Dolly the sheep. All rights reserved. Cell-Extrinsic Regulation of Gene Expression.

Figure 2: Microarray data collected at different times during metamorphosis reveals the effects of the ecdysone pulse on many downstream genetic pathways. A Changes in ecdysone levels affect the glycolytic pathway. Levels of a number of enzymes involved in this pathway are decreased as a result of the ecdysone pulse; these enzymes are listed in red next to the reactions they catalyze.

B This array shows expression changes in various structural and regulatory genes involved in muscle formation myogenesis in response to the ecdysone pulse.

C This array shows how the ecdysone pulse alters expression of multiple genes involved in central nervous system restructuring, apoptosis, and cellular differentiation during metamorphosis.

In both of the microarrays, red means that the gene was downregulated, while green means that the gene was upregulated.

Expression levels were measured at various points before and after pupal formation PF. Science , — Figure Detail. Cell-Intrinsic Regulation of Gene Expression. Figure 3: Epigenetic gene regulation during mammalian development. This figure depicts key developmental events together with global epigenetic modifications and gene expression patterns.

Very early in development, DNA methylation is erased. In addition, pluripotency-associated genes begin to be expressed, and developmental genes are repressed by the PcG protein system and H3K27 methylation.

During the differentiation of pluripotent cells such as embryonic stem ES cells, pluripotency-associated genes are repressed, potentially permanently, as a result of DNA methylation. At the same time, developmental genes begin to be expressed, and there is an increase in H3K4 methylation.

During the early development of primordial germ cells PGCs , DNA methylation and repressive histone modifications such as H3K9 methylation are also erased. Pluripotency-associated genes are re-expressed during a time window that allows embryonic germ cells to be derived in culture. Imprinted genes are demethylated during this period, and developmental genes are expressed afterwards. Flexible histone marks such as H3K27 methylation enable developmental genes to be silenced for a short time in pluripotent cells.

By contrast, DNA methylation enables the stable silencing of imprinted genes, transposons, and some pluripotency-associated genes. Nature , References and Recommended Reading Bernstein, B. Cell , — Giles, J. Nature , link to article Gurdon, J. Developmental Cell 10 , — Puri, P.

Molecular Cell 1 , 35—45 Reik, W. Nature , — link to article Vucic, E. Pharmacogenomics 9 , — White, K. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel.