Introductory Biology

10.2 Gene Regulation + Structure


Not every gene can be expressed all the time: cone cell (how you can see color), skin cell, muscle cell and nerve cells. All of these cells make very different proteins and different RNA is being made. Each one of these cells has to have their own set of genes.

There are two steps in Transcriptional control: activation and repression. In prokaryotes, nuclear envelopes are lacked and is controlled by “ON-OFF” switches. The Lac Operon is one of the gene regulation in prokaryotes. The genes that breaks down lactose are switched off, as long as the lactose is absent from the cell. But normally, the E-coli uses glucose for its energy. In repression, the inducers turn the cell ON and binds to the repressor, allowing the RNA polymerase to bind. The repressors block RNA polymerase so it cannot read the DNA allowing it to turn OFF. The mRNA is translated and it turns into a protein, which acts as a repressor that is attracted to the operator. The repressor blocks the RNA polymerase from transcribing other lac operon genes. When the lactose is absent, the genes to digest lactose are inactive and turns the switch OFF.  When the lactose is present, the cell responds by turning on the genes to break the lactose. The repressor grabs onto the lactose and lets go of the DNA. When lactose is gone again, the repressor goes back to the operator. When the lactose is present, the genes to digest lactose are active and let the RNA polymerase to continue moving along the DNA.

There are more DNA in eukaryotic cells than prokaryotic cells. There are many ways to process the gene expression because the nuclear envelope separates transcription from translation. Transcription factors are regulatory proteins that RNA polymerase need in order to bind to the promoter region of a gene. The enhancers are regions of the DNA where the activators (switch genes ON) bind to enhancers. Enhancers: are on the DNA. Activators: are transcription factors. Activators + enhancers = together acts as a transcription factor. The RNA polymerase can only bind with the help of transcription factors and lead to gene expression. Transcription only begins when a complete set of transcription factors are present for a given gene. Genes are silent (no repressors).

======= Gene Structure ======

There are 2 types of DNA in a pre RNA gene: exons and introns. There will most likely be one less introns than exons in the pre RNA strand. Exons: are the bases of making the protein and gets expressed/translated into proteins. Introns: interrupt the DNA coding region and have to be removed/cut out. The introns must be removed from the RNA before it can be translated.

**RNA splicing is when the introns get removed and the exons gets spliced together. The snRNP contains RNA and protein. Exons can be cut out as well, depending on which cell it is and what protein they have to make. Transposons: the exons can move around. This allows new combinations of exons and makes new genes, which explains evolution, and they move from one chromosome to another.

Mutations are very rare and only appear in about a billion nucleotides per generation. Point mutations is when one or a few nulceotides are changed and substitution mutations replace one nucleotide with another. The replacement have one of these three effects:

  • no effect (UGU -> UGC both code for cysteine)
  • may alter a single amino acid (UGU = cystein, CGU = arginine)
  • may change a codon to a stop codon (UGC = cysteine, UGA = stop)

Frameshift mutation cause a gene to be read in the wrong three nucleotide sequence. There are also three types of frameshift mutations:

  • insertion (addition of a nucleotide)
  • deletion (removal of a nucleotide)
  • change all downstream codons, often serious

Gene Sequencing Determines the Sequence of Nucleotides in DNA. It is used to identify genetic disorders, identify genes, establish evolutionary relationships, and used as forensic evidence in criminal cases. Each gene will be known in the normal and damaged sequence and can tell us how to fix the diseases. The Human Genome Project was produced to make a complete map of the human genetic blueprint, identifying between 26,000 and 40,000 genes. Mutagenes generate mutations like, x-rays, chemicals, ultraviolet radiation, and etc. When the DNA is getting copied, they do not know what to put.

One thought on “10.2 Gene Regulation + Structure

  1. Yurika,

    Excellent job of covering the ideas in 10.2 regarding gene structure and function. The concepts are difficult, and you indicate good understanding. You’ve also put some thought into organizing your ideas. You should do well on the test.

    Mr. F.

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