Genetics

  • Transposons Shifting Segments of the Genome

    Transposons, also called transposable elements, are mobile genetic elements that generally have only modest target site selectively and can thus insert themselves into many different DNA sites. In transposition, a specific enzyme, usually encoded by the transposon and called a transpose, acts on a specific DNA sequence at each end of the transposon (first disconnecting it from the flanking DNA)…

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  • Southern Blot

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  • Spermatogenesis

    In male animals, each meiosis produces four equal-sized sperm cells in a process called spermatogenesis. In vertebrates, a cell type in the testes known as a spermatogonium produces primary spermatocytes, as well as additional spermatogonia, by mitosis. The primary spermatocytes then undergo meiosis. After the first meiotic division, these cells are known as secondary spermatocytes; after the second meiotic division,…

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  • Spliceosome

    According to the current model of pre-mRNA splicing, the five splicing snRNPs (small nuclear ribonucleoproteins) are thought to assemble on the pre mRNA, forming a large ribonucleoprotein complex called a spliceosome (Protein-RNA complex that removes introns in eukaryotic nuclear RNAs.), named by J. Abelson and E. Brody. The splicing apparatus in eukaryotic messenger RNAs consists of several components called small…

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  • Stages of Meiosis

    Premeiotic cells have two copies of each chromosome (2n), one derived from the paternal parent and one from the maternal parent. For simplicity, the paternal and maternal homologs of only one chromosome arediagrammed. All chromosomes are replicated during the S phase before the first meiotic division, giving a 4n chromosomal complement. Cohesin complexes (not shown) link the sister chromatids composing…

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  • Thymine Dimer

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  • Transcription and Enhacers

    Like bacteria, eukaryotes use gene regulatory proteins (activates and repressors) to regulate the expression of their genes but in somewhat different way. The DNA sites to witch the eukaryote gene activates bound were originally termed enhancers, since their presence “enhanced”, or increased, the rate of transcription dramatically. It came as a surprise when, in 1979, in was discovered that those…

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  • Tryptophan Repressor

    The Escherichia coli bacterium have a single circular DNA which consist of 4.6 million nucleotides. E. Coli genome encodes more than 4000 proteins. Since their environmental condition is regularly changing, bacterial organisms don’t generally need to express their whole supplement of enzymes and proteins. For instance, if there is external tryptophan amino acids available, bacteria does not need to synthesize…

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  • Tumor Suppressor Gene

    Tumor-suppressor genes generally encode proteins that in one way or another inhibit cell proliferation. Loss-offunction mutations in one or more of these “brakes” contribute to the development of many cancers. Five broad classes of proteins are generally recognized as being encoded by tumor-suppressor genes: Intracellular proteins that regulate or inhibit progression through a specific stage of the cell cycle (e.g.,…

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