Gene Expression Regulation and Cancer Causes

Regulation of Gene Expression

Cells do not continuously synthesize proteins, which could result in metabolic chaos. There must be a regulation. Jacob and Monod devised a model for gene regulation in bacteria called Operon. An operon is a set of genes on the chromosome, fairly close together, that encode proteins involved in related metabolic processes. In each operon, there are two classes of genes:

• Structural genes

  (z, A) that code for the synthesis of proteins in a given process.

• Regulator gene

  (I) that codes for the synthesis of a repressor protein, which controls the expression of structural genes.

There are also two regions close to these genes whose base sequences influence regulation:

• The promoter (P)

  Next to the structural genes, this is the sequence where RNA polymerase recognizes and binds, initiating gene transcription.

• The operator (O)

  This region, sandwiched between the promoter and the structural gene sequence, is recognized by the repressor. When the repressor is active and bound, it blocks RNA polymerase, preventing transcription of the structural genes, resulting in gene repression. The repressor is inactivated by an inducer molecule, such as lactose, which forms the substrate.

Cancer: Genetic and Environmental Causes

Cancer occurs when a group of cells fails to control cell proliferation and differentiation, replicating uncontrollably. The resulting cell mass damages healthy tissue and can even produce metastasis.

Carcinogens: In the twentieth century, the link between cancer and radiation was established.

• Genetic causes of cancer:

  Rous demonstrated the existence of infectious viruses capable of producing cancer in chickens. The Kaposi sarcoma was due to a gene of the virus called oncogene. Sarcoma is a malignant tumor originating from muscle or blood vessel tissue.

• Oncogenes:

  In human cancers, viral genes are sometimes human genes that viruses have trapped. Sometimes, viruses activate other host genes that remain inactive. It was discovered that proto-oncogenes encode proteins involved in cell division, such as:

  • Growth factors.
  • Membrane receptors of growth factors.
  • Intracellular proteins that propagate the growth signal.
  • Nuclear proteins that control cell division.

  Cellular proliferation and differentiation are often controlled by transcription factors that stimulate or inhibit.