gene expression

Examples of gene expression in the following topics:

• Prokaryotic versus Eukaryotic Gene Expression

  • Prokaryotes regulate gene expression by controlling the amount of transcription, whereas eukaryotic control is much more complex.
  • To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell.
  • Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
  • The regulation of gene expression can occur at all stages of the process .
  • Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.

• Cancer and Transcriptional Control

  • Increased transcriptional activation of genes result in alterations of cell growth leading to abnormal gene expression, as seen in cancer.
  • Alterations in cells that give rise to cancer can affect the transcriptional control of gene expression.
  • This could also lead to the increased transcription and aberrant gene expression that is seen in cancer cells.
  • Researchers have been investigating how to control the transcriptional activation of gene expression in cancer.
  • Transcription factors, especially some that are proto-oncogenes or tumor suppressors, help regulate the cell cycle; however, when regulation gives rise to cancer cells, then transcriptional control of gene expression is affected.

• The Process and Purpose of Gene Expression Regulation

  • At any given time, only a subset of all of the genes encoded by our DNA are expressed and translated into proteins.
  • The expression of specific genes is a highly-regulated process with many levels and stages of control.
  • In this section, you will learn about the various methods of gene regulation and the mechanisms used to control gene expression, such as: epigenetic, transcriptional, post-transcriptional, translational, and post-translational controls in eukaryotic gene expression, and transcriptional control in prokaryotic gene expression.
  • The genetic content of each somatic cell in an organism is the same, but not all genes are expressed in every cell.
  • The control of which genes are expressed dictates whether a cell is (a) an eye cell or (b) a liver cell.

• Cell Signaling and Gene Expression

  • Gene expression, vital for cells to function properly, is the process of turning on a gene to produce RNA and protein.
  • The process of turning on a gene to produce RNA and protein is called gene expression.
  • The regulation of gene expression conserves energy and space.
  • The control of gene expression is extremely complex.
  • The regulation of gene expression can occur at all stages of the process.

• Cancer and Translational Control

  • Scientists are using what is known about the regulation of gene expression in disease states, including cancer, to develop new ways to treat and prevent disease development.
  • Many scientists are designing drugs on the basis of the gene expression patterns within individual tumors.
  • With an increased understanding of gene regulation and gene function, medicines can be designed to specifically target diseased cells without harming healthy cells.
  • Undoubtedly, more targeted therapies will be developed as scientists learn more about how gene expression changes can cause cancer .
  • Scientists are using knowledge of the regulation of gene expression in individual cancers to develop new ways to treat target diseased cells and prevent the disease from occurring.

• Epigenetic Control: Regulating Access to Genes within the Chromosome

  • Both the packaging of DNA around histone proteins, as well as chemical modifications to the DNA or proteins, can alter gene expression.
  • These changes to DNA are inherited from parent to offspring, such that while the DNA sequence is not altered, the pattern of gene expression is passed to the next generation.
  • When nucleosomes are spaced closely together (top), transcription factors cannot bind and gene expression is turned off.
  • Transcription factors can bind, allowing gene expression to occur.
  • Modifications affect nucleosome spacing and gene expression.

• Altered Gene Expression in Cancer

  • Cancer, a disease of altered gene expression, is the result of gene mutations or dramatic changes in gene regulation.
  • Cancer can be described as a disease of altered gene expression.
  • There are many proteins that are turned on or off (gene activation or gene silencing) that dramatically alter the overall activity of the cell.
  • A gene that is not normally expressed in that cell can be switched on and expressed at high levels.
  • This can be the result of gene mutation or changes in gene regulation (epigenetic, transcription, post-transcription, translation, or post-translation).

• Transcriptional Enhancers and Repressors

  • Enhancers increase the rate of transcription of genes, while repressors decrease the rate of transcription.
  • In some eukaryotic genes, there are regions that help increase or enhance transcription.
  • These regions, called enhancers, are not necessarily close to the genes they enhance.
  • They can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or may be thousands of nucleotides away.
  • A corepressor is a protein that decreases gene expression by binding to a transcription factor that contains a DNA-binding domain.

• Epistasis

  • Epistasis occurs when one gene masks or interferes with the expression of another.
  • Genes may also oppose each other with one gene modifying the expression of another.
  • In epistasis, the interaction between genes is antagonistic: one gene masks or interferes with the expression of another.
  • Epistasis can also occur when a dominant allele masks expression at a separate gene.
  • Homozygous recessive expression of the W gene (ww) coupled with homozygous dominant or heterozygous expression of the Y gene (YY or Yy) generates yellow fruit, while the wwyy genotype produces green fruit.

• Epigenetic Alterations in Cancer

  • Silencing genes through epigenetic mechanisms is very common in cancer cells and include modifications to histone proteins and DNA that are associated with silenced genes.
  • Histone proteins that surround that region lack the acetylation modification (the addition of an acetyl group) that is present when the genes are expressed in normal cells.
  • When these modifications occur, the gene present in that chromosomal region is silenced.
  • In cancer cells, silencing genes through epigenetic mechanisms is a common occurrence.
  • Describe the role played by epigenetic alterations to gene expression in the development of cancer