{"id":186,"date":"2014-10-31T05:21:01","date_gmt":"2014-10-31T05:21:01","guid":{"rendered":"http:\/\/courses.candelalearning.com\/novabiology\/?post_type=chapter&p=186"},"modified":"2019-05-13T18:11:20","modified_gmt":"2019-05-13T18:11:20","slug":"cell-division","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/nemcc-biology1v2\/chapter\/cell-division\/","title":{"raw":"Cell Division","rendered":"Cell Division"},"content":{"raw":"
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Learning Objectives<\/h3>\r\n
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\r\n\r\nBy the end of this section, you will be able to:\r\n
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\r\n
\r\n
    \r\n \t
  • Describe the structure of prokaryotic and eukaryotic genetic make-up<\/li>\r\n \t
  • Distinguish between chromosomes, genes, and traits<\/li>\r\n \t
  • Describe the mechanisms of chromosome compaction<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
    \r\n
    \r\n

    The continuity of life from one cell to another has its foundation in the reproduction of cells by way of the cell cycle. The cell cycle is an<\/span> orderly sequence of events that describes the stages of a cell\u2019s life from the division of a single parent cell to the production of two new<\/span> daughter cells.<\/span><\/p>\r\n\r\n

    \r\n

    Genomic DNA<\/h2>\r\n
    <\/figure>\r\nThe cellular DNA, packaged as a double-stranded DNA molecule, is called its genome. In prokaryotes, the genome is composed of a single, double-stranded DNA molecule in a loop located within the nucleoid(Figure 1).\r\n\r\n[caption id=\"attachment_1366\" align=\"aligncenter\" width=\"544\"]\"The Figure 1. Prokaryotes, including bacteria and archaea, have a single, circular chromosome located in a central region called the nucleoid.[\/caption]\r\n
    <\/figure>\r\n[caption id=\"attachment_1363\" align=\"alignright\" width=\"450\"]\"The Figure 2. There are 23 pairs of homologous chromosomes in a female human somatic cell. The condensed chromosomes are viewed within the nucleus (top), removed from a cell in mitosis and spread out on a slide (right), and artificially arranged according to length (left); an arrangement like this is called a karyotype. In this image, the chromosomes were exposed to fluorescent stains for differentiation of the different chromosomes. A method of staining called \u201cchromosome painting\u201d employs fluorescent dyes that highlight chromosomes in different colors. (credit: National Human Genome Project\/NIH)[\/caption]\r\n\r\nIn eukaryotes, the genome consists of several double-stranded linear DNA molecules (Figure 2). Each species of eukaryotes has a characteristic number of chromosomes in the nuclei of its cells.\u00a0 Diploid describes a nucleus containing two copies of genetic material or a complete set of chromosomes.\u00a0 For humans, diploid would be shown as 2n = 46.\u00a0 Haploid, found in our sex cells, would have only one copy of the genetic material or a half a set of chromosomes.\u00a0 So, n = 23 for humans.\r\n

    Matched pairs of chromosomes in a diploid organism are called homologous (\u201csame knowledge\u201d) chromosomes<\/span>. Homologous chromosomes are the same length and have genes in exactly the same location, or locus. Genes, the functional units of chromosomes, determine specific characteristics.\u00a0 Traits are the variations of those characteristics. An example would be hair color with traits that are blonde, brown, or black.<\/p>\r\n\u00a0The variation of individuals within a species is due to the specific combination of the genes inherited from both parents. Even a slightly altered sequence within a gene can result in an alternative trait.\u00a0 For example, there are three possible gene sequences on the human chromosome coding for blood type: sequence A, sequence B, and sequence O. Because all diploid human cells have two copies of the chromosome for blood type, the blood type(trait) is determined by which two versions of the gene is inherited.\r\n

    Minor variations of traits, such as blood type and eye color, contribute to the natural variation found within a species. The sex chromosomes, X and Y, are the single exception to the rule of homologous chromosome uniformity.\u00a0 The X and Y chromosomes do have variations to accurately produce gametes, but other slight variations do exist.<\/p>\r\n\r\n<\/section>

    \r\n

    Eukaryotic Chromosomal Structure and Compaction<\/h1>\r\n
    <\/figure>\r\n[caption id=\"attachment_1367\" align=\"alignright\" width=\"450\"]\"There Figure 3. Double-stranded DNA wraps around histone proteins to form nucleosomes that have the appearance of \u201cbeads on a string.\u201d The nucleosomes are coiled into a 30-nm chromatin fiber. When a cell undergoes mitosis, the chromosomes condense even further.[\/caption]\r\n\r\nDNA must be tightly packaged to fit in the cell\u2019s nucleus. At the same time, it must also be readily accessible for gene expression.\u00a0 During some stages of the cell cycle, the long strands of DNA are condensed into compact chromosomes.\u00a0 Chromosomes are compacted in a number of ways to include:\r\n\r\n(1)\u00a0 short stretches of the DNA double helix wrap around a core of eight histone proteins at regular intervals along the chromosome forming nucleosome(Figure 3);\r\n\r\n(2)\u00a0 nucleosomes coil into chromatin fiber;\u00a0 further shortens the chromosome; forms chromatin fiber\r\n\r\n(3)\u00a0 proteins are used to pack the chromatin;\u00a0 ensure each chromosome (in a non-dividing cell) occupies a particular area of the nucleus that does not overlap with any other chromosome (see the top image in Figure 3).\r\n\r\nDNA replication occurs in interphase during the S phase of the cell cycle.\u00a0 After replication, a chromosome is composed of two linked sister chromatids held together at a compacted region called the centromere.\r\n
    \r\n

    Link to Learning<\/h3>\r\nThis animation illustrates the different levels of chromosome packing:\r\n\r\nhttps:\/\/youtu.be\/gbSIBhFwQ4s\r\n\r\n<\/div>\r\n

    Section Summary<\/h1>\r\n

    Prokaryotes have a single looped chromosome composed of double-stranded DNA in the nucleoid.\u00a0 Eukaryotes have double-stranded\u00a0 linear chromosomes composed of chromatin in the nucleus.\u00a0 A full set of matched chromosomes is referred to as diploid.\u00a0 Haploid is having a half a set of chromosomes. Genes are segments of DNA that code for a specific protein. An organism\u2019s traits are determined by the genes inherited from each parent. Duplicated chromosomes are composed of two sister chromatids held together by the centromere.\u00a0 Chromosomes are compacted using a variety of mechanisms during the cell cycle which is necessary for chromosomal segregation during mitosis.<\/p>\r\nhttps:\/\/www.openassessments.org\/assessments\/473\r\n\r\n

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    Additional Self Check Questions<\/h3>\r\n
    \r\n
    \r\n
    \r\n\r\n1. Define diploid and haploid.\r\n\r\n<\/div>\r\n<\/section><\/div>\r\n
    \r\n
    \r\n
    <\/div>\r\n
    \r\n

    2.\u00a0 Eukaryotic chromosomes are thousands of times longer than a typical cell. Explain how chromosomes can fit inside a eukaryotic nucleus.<\/p>\r\n\r\n<\/section><\/div>\r\n<\/section><\/div>\r\n<\/section><\/div>\r\n

    \r\n
    \r\n
    \r\n

    AnswERs<\/h3>\r\n \r\n\r\n
    1. Diploid is a full set of matched chromosomes inside a cell nucleus.\u00a0 Haploid is a half a set of chromosomes.\u00a0 Diploid is represented as 2n, while haploid is represented as n.\u00a0<\/section>
    <\/section>
    <\/section>
    2. The DNA double helix is wrapped around histone proteins to form structures called nucleosomes. Nucleosomes are coiled into a chromatin fiber. During cell division, chromatin is further condensed. \u00a0<\/section><\/div>\r\n<\/section><\/div>\r\n<\/section><\/div>\r\n<\/section><\/section><\/div>\r\n<\/div>","rendered":"
    \n

    Learning Objectives<\/h3>\n
    \n
    \n

    By the end of this section, you will be able to:<\/p>\n

    \n
    \n
    \n
      \n
    • Describe the structure of prokaryotic and eukaryotic genetic make-up<\/li>\n
    • Distinguish between chromosomes, genes, and traits<\/li>\n
    • Describe the mechanisms of chromosome compaction<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
      \n
      \n

      The continuity of life from one cell to another has its foundation in the reproduction of cells by way of the cell cycle. The cell cycle is an<\/span> orderly sequence of events that describes the stages of a cell\u2019s life from the division of a single parent cell to the production of two new<\/span> daughter cells.<\/span><\/p>\n

      \n

      Genomic DNA<\/h2>\n
      <\/figure>\n

      The cellular DNA, packaged as a double-stranded DNA molecule, is called its genome. In prokaryotes, the genome is composed of a single, double-stranded DNA molecule in a loop located within the nucleoid(Figure 1).<\/p>\n

      \"The<\/p>\n

      Figure 1. Prokaryotes, including bacteria and archaea, have a single, circular chromosome located in a central region called the nucleoid.<\/p>\n<\/div>\n

      <\/figure>\n
      \"The<\/p>\n

      Figure 2. There are 23 pairs of homologous chromosomes in a female human somatic cell. The condensed chromosomes are viewed within the nucleus (top), removed from a cell in mitosis and spread out on a slide (right), and artificially arranged according to length (left); an arrangement like this is called a karyotype. In this image, the chromosomes were exposed to fluorescent stains for differentiation of the different chromosomes. A method of staining called \u201cchromosome painting\u201d employs fluorescent dyes that highlight chromosomes in different colors. (credit: National Human Genome Project\/NIH)<\/p>\n<\/div>\n

      In eukaryotes, the genome consists of several double-stranded linear DNA molecules (Figure 2). Each species of eukaryotes has a characteristic number of chromosomes in the nuclei of its cells.\u00a0 Diploid describes a nucleus containing two copies of genetic material or a complete set of chromosomes.\u00a0 For humans, diploid would be shown as 2n = 46.\u00a0 Haploid, found in our sex cells, would have only one copy of the genetic material or a half a set of chromosomes.\u00a0 So, n = 23 for humans.<\/p>\n

      Matched pairs of chromosomes in a diploid organism are called homologous (\u201csame knowledge\u201d) chromosomes<\/span>. Homologous chromosomes are the same length and have genes in exactly the same location, or locus. Genes, the functional units of chromosomes, determine specific characteristics.\u00a0 Traits are the variations of those characteristics. An example would be hair color with traits that are blonde, brown, or black.<\/p>\n

      \u00a0The variation of individuals within a species is due to the specific combination of the genes inherited from both parents. Even a slightly altered sequence within a gene can result in an alternative trait.\u00a0 For example, there are three possible gene sequences on the human chromosome coding for blood type: sequence A, sequence B, and sequence O. Because all diploid human cells have two copies of the chromosome for blood type, the blood type(trait) is determined by which two versions of the gene is inherited.<\/p>\n

      Minor variations of traits, such as blood type and eye color, contribute to the natural variation found within a species. The sex chromosomes, X and Y, are the single exception to the rule of homologous chromosome uniformity.\u00a0 The X and Y chromosomes do have variations to accurately produce gametes, but other slight variations do exist.<\/p>\n<\/section>\n

      \n

      Eukaryotic Chromosomal Structure and Compaction<\/h1>\n
      <\/figure>\n
      \"There<\/p>\n

      Figure 3. Double-stranded DNA wraps around histone proteins to form nucleosomes that have the appearance of \u201cbeads on a string.\u201d The nucleosomes are coiled into a 30-nm chromatin fiber. When a cell undergoes mitosis, the chromosomes condense even further.<\/p>\n<\/div>\n

      DNA must be tightly packaged to fit in the cell\u2019s nucleus. At the same time, it must also be readily accessible for gene expression.\u00a0 During some stages of the cell cycle, the long strands of DNA are condensed into compact chromosomes.\u00a0 Chromosomes are compacted in a number of ways to include:<\/p>\n

      (1)\u00a0 short stretches of the DNA double helix wrap around a core of eight histone proteins at regular intervals along the chromosome forming nucleosome(Figure 3);<\/p>\n

      (2)\u00a0 nucleosomes coil into chromatin fiber;\u00a0 further shortens the chromosome; forms chromatin fiber<\/p>\n

      (3)\u00a0 proteins are used to pack the chromatin;\u00a0 ensure each chromosome (in a non-dividing cell) occupies a particular area of the nucleus that does not overlap with any other chromosome (see the top image in Figure 3).<\/p>\n

      DNA replication occurs in interphase during the S phase of the cell cycle.\u00a0 After replication, a chromosome is composed of two linked sister chromatids held together at a compacted region called the centromere.<\/p>\n

      \n

      Link to Learning<\/h3>\n

      This animation illustrates the different levels of chromosome packing:<\/p>\n