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Unit 9: Regulation of Gene Expression

  • 9.1: Regulation of Gene Expression in Bacteria
    Within its tiny cell, the bacterium E. coli contains all the genetic information it needs to metabolize, grow, and reproduce. It can synthesize every organic molecule it needs from glucose and a number of inorganic ions. Many of the genes in E. coli are expressed constitutively; that is, they are always turned "on". Others, however, are active only when their products are needed by the cell, so their expression must be regulated.
  • 9.2: The Tryptophan Repressor
    In E. coli, the synthesis of the amino acid tryptophan from precursors available to the cell requires 5 enzymes. The genes encoding these are clustered together in a single operon with its own promoter and operator. When tryptophan is available to the cell, its presence shuts down the operon.
  • 9.3: Regulation of Gene Expression in Eukaryotes
    There are several methods used by eukaryotes. regulate gene expression. Including altering the rate of transcription of the gene, altering the rate at which RNA transcripts are processed, altering the stability of messenger RNA molecules and altering the efficiency with which ribosomes translate the mRNA into a polypeptide.
  • 9.4: Steroid Response Elements
    Steroid hormone receptors are proteins that have a binding site for a particular steroid molecule. Their response elements are DNA sequences that are bound by the complex of the steroid bound to its receptor. The response element is part of the promoter of a gene. Binding by the receptor activates or represses, as the case may be, the gene controlled by that promoter. It is through this mechanism that steroid hormones turn genes on (or off).
  • 9.5: Epigenetics
    Epigenetics can be defined as a change in phenotype that is heritable but does not involve a change in the nucleotide sequence in DNA; that is, a change in genotype. This definition is very broad encompassing a variety of phenomena.
  • 9.6: Visualization of Transcription and Translation in Bacteria
    Each polysome is attached to the DNA fiber by a complex of proteins that includes a molecule of RNA polymerase. Thus the DNA is transcribed by RNA polymerase molecules moving from top to bottom, and the growing mRNA molecules are translated by ribosomes moving in a proximal -> distal direction. IIn E. coli, then, and probably in all bacteria, the transcription of DNA into mRNA and the translation of mRNA into polypeptides (not visible here) are closely coordinated in both time and space.
  • 9.7: Footprinting
    Footprinting is a method for determining the exact DNA sequence to which a particular DNA-binding protein binds.
  • 9.8: Chromatin Immunoprecipitation
    Many DNA-binding proteins, such as transcription factors, bind to specific sequences of nucleotides in, for example, promoters and enhancers of genes. The binding of protein to DNA is done by noncovalent forces and is easily reversible. The identification of a specific site in DNA bound by a particular protein at a particular time can be discovered by the technique of chromatin immunoprecipitation.
  • 9.9: Isolating Transcription Factors
    Transcription factors are extraordinarily diverse, and any one factor represents only a tiny fraction of the protein molecules present in the cell. This page describes how one can isolate and purify such rare molecules.
  • 9.10: Palindromes
    A palindrome is a sequence of letters and/or words, that reads the same forwards and backwards. Palindromes also occur in a DNA and there are two types.
  • 9.11: Cell-specific gene expression
  • 9.12: Imprinted Genes
    Imprinted genes are genes whose expression is determined by the parent that contributed them. Imprinted genes violate the usual rule of inheritance that both alleles in a heterozygote are equally expressed.
  • 9.13: Ribozymes
    Some RNA molecules can act as enzymes; that is, catalyze covalent changes in the structure of substrates (most of which are also RNA molecules). Catalytic RNA molecules are called ribozymes.

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