{"id":1696,"date":"2014-10-21T03:46:47","date_gmt":"2014-10-21T03:46:47","guid":{"rendered":"https:\/\/courses.candelalearning.com\/apvccs\/?post_type=chapter&p=1696"},"modified":"2016-08-03T21:45:52","modified_gmt":"2016-08-03T21:45:52","slug":"the-nucleus-and-dna-replication","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/atd-herkimer-biologyofaging\/chapter\/the-nucleus-and-dna-replication\/","title":{"raw":"The Nucleus and DNA Replication","rendered":"The Nucleus and DNA Replication"},"content":{"raw":"
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Nucleus<\/h3>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nThe nucleus is the largest and most prominent of a cell\u2019s organelles (Figure\u00a03.19<\/a>). The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins. Interestingly, some cells in the body, such as muscle cells, contain more than one nucleus (Figure\u00a03.20<\/a>), which is known as multinucleated. Other cells, such as mammalian red blood cells (RBCs), do not contain nuclei at all. RBCs eject their nuclei as they mature, making space for the large numbers of hemoglobin molecules that carry oxygen throughout the body (Figure\u00a03.21<\/a>). Without nuclei, the life span of RBCs is short, and so the body must produce new ones constantly.\r\n
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\"This<\/div>\r\n<\/div>\r\n
Figure\u00a03.19.\u00a0The Nucleus<\/strong><\/address>
The nucleus is the control center of the cell. The nucleus of living cells contains the genetic material that determines the entire structure and function of that cell.<\/address>
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Figure\u00a03.20.\u00a0Multinucleate Muscle Cell<\/strong>F<\/address>
Unlike cardiac muscle cells and smooth muscle cells, which have a single nucleus, a skeletal muscle cell contains many nuclei, and is referred to as \u201cmultinucleated.\u201d These muscle cells are long and fibrous (often referred to as muscle fibers). During development, many smaller cells fuse to form a mature muscle fiber. The nuclei of the fused cells are conserved in the mature cell, thus imparting a multinucleate characteristic to mature muscle cells. LM \u00d7 104.3. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/address>
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Figure\u00a03.21.\u00a0Red Blood Cell Extruding Its Nucleus<\/strong><\/address>
Mature red blood cells lack a nucleus. As they mature, erythroblasts extrude their nucleus, making room for more hemoglobin. The two panels here show an erythroblast before and after ejecting its nucleus, respectively. (credit: modification of micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/address>
\u00a0<\/address><\/div>\r\nInside the nucleus lies the blueprint that dictates everything a cell will do and all of the products it will make. This information is stored within DNA. The nucleus sends \u201ccommands\u201d to the cell via molecular messengers that translate the information from DNA. Each cell in your body (with the exception of germ cells) contains the complete set of your DNA. When a cell divides, the DNA must be duplicated so that the each new cell receives a full complement of DNA. The following section will explore the structure of the nucleus and its contents, as well as the process of DNA replication.\r\n
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Organization of the Nucleus and Its DNA<\/h2>\r\n<\/div>\r\nLike most other cellular organelles, the nucleus is surrounded by a membrane called the\u00a0nuclear envelope<\/em>. This membranous covering consists of two adjacent lipid bilayers with a thin fluid space in between them. Spanning these two bilayers are nuclear pores. A\u00a0nuclear pore<\/em>\u00a0is a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and the cytoplasm. Proteins called pore complexes lining the nuclear pores regulate the passage of materials into and out of the nucleus. Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids. There also can be a dark-staining mass often visible under a simple light microscope, called anucleolus<\/em>\u00a0(plural = nucleoli). The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of ribosomes. Once synthesized, newly made ribosomal subunits exit the cell\u2019s nucleus through the nuclear pores. The genetic instructions that are used to build and maintain an organism are arranged in an orderly manner in strands of DNA. Within the nucleus are threads of\u00a0chromatin<\/em>\u00a0composed of DNA and associated proteins (Figure\u00a03.22<\/a>). Along the chromatin threads, the DNA is wrapped around a set of\u00a0histone<\/em>\u00a0proteins. Anucleosome<\/em>\u00a0is a single, wrapped DNA-histone complex. Multiple nucleosomes along the entire molecule of DNA appear like a beaded necklace, in which the string is the DNA and the beads are the associated histones. When a cell is in the process of division, the chromatin condenses into chromosomes, so that the DNA can be safely transported to the \u201cdaughter cells.\u201d The\u00a0chromosome<\/em>\u00a0is composed of DNA and proteins; it is the condensed form of chromatin. It is estimated that humans have almost 22,000 genes distributed on 46 chromosomes.\r\n
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\"This<\/div>\r\n<\/div>\r\n
Figure\u00a03.22.\u00a0DNA Macrostructure<\/strong><\/address>
Strands of DNA are wrapped around supporting histones. These proteins are increasingly bundled and condensed into chromatin, which is packed tightly into chromosomes when the cell is ready to divide.<\/address>
\u00a0<\/address><\/div>\r\n<\/div>","rendered":"
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Nucleus<\/h3>\n<\/div>\n<\/div>\n<\/div>\n

The nucleus is the largest and most prominent of a cell\u2019s organelles (Figure\u00a03.19<\/a>). The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins. Interestingly, some cells in the body, such as muscle cells, contain more than one nucleus (Figure\u00a03.20<\/a>), which is known as multinucleated. Other cells, such as mammalian red blood cells (RBCs), do not contain nuclei at all. RBCs eject their nuclei as they mature, making space for the large numbers of hemoglobin molecules that carry oxygen throughout the body (Figure\u00a03.21<\/a>). Without nuclei, the life span of RBCs is short, and so the body must produce new ones constantly.<\/p>\n

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\"This<\/div>\n<\/div>\n
Figure\u00a03.19.\u00a0The Nucleus<\/strong><\/address>\n
The nucleus is the control center of the cell. The nucleus of living cells contains the genetic material that determines the entire structure and function of that cell.<\/address>\n
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\"This<\/div>\n<\/div>\n
Figure\u00a03.20.\u00a0Multinucleate Muscle Cell<\/strong>F<\/address>\n
Unlike cardiac muscle cells and smooth muscle cells, which have a single nucleus, a skeletal muscle cell contains many nuclei, and is referred to as \u201cmultinucleated.\u201d These muscle cells are long and fibrous (often referred to as muscle fibers). During development, many smaller cells fuse to form a mature muscle fiber. The nuclei of the fused cells are conserved in the mature cell, thus imparting a multinucleate characteristic to mature muscle cells. LM \u00d7 104.3. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/address>\n
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\"This<\/div>\n<\/div>\n
Figure\u00a03.21.\u00a0Red Blood Cell Extruding Its Nucleus<\/strong><\/address>\n
Mature red blood cells lack a nucleus. As they mature, erythroblasts extrude their nucleus, making room for more hemoglobin. The two panels here show an erythroblast before and after ejecting its nucleus, respectively. (credit: modification of micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/address>\n
\u00a0<\/address>\n<\/div>\n

Inside the nucleus lies the blueprint that dictates everything a cell will do and all of the products it will make. This information is stored within DNA. The nucleus sends \u201ccommands\u201d to the cell via molecular messengers that translate the information from DNA. Each cell in your body (with the exception of germ cells) contains the complete set of your DNA. When a cell divides, the DNA must be duplicated so that the each new cell receives a full complement of DNA. The following section will explore the structure of the nucleus and its contents, as well as the process of DNA replication.<\/p>\n

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Organization of the Nucleus and Its DNA<\/h2>\n<\/div>\n

Like most other cellular organelles, the nucleus is surrounded by a membrane called the\u00a0nuclear envelope<\/em>. This membranous covering consists of two adjacent lipid bilayers with a thin fluid space in between them. Spanning these two bilayers are nuclear pores. A\u00a0nuclear pore<\/em>\u00a0is a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and the cytoplasm. Proteins called pore complexes lining the nuclear pores regulate the passage of materials into and out of the nucleus. Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids. There also can be a dark-staining mass often visible under a simple light microscope, called anucleolus<\/em>\u00a0(plural = nucleoli). The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of ribosomes. Once synthesized, newly made ribosomal subunits exit the cell\u2019s nucleus through the nuclear pores. The genetic instructions that are used to build and maintain an organism are arranged in an orderly manner in strands of DNA. Within the nucleus are threads of\u00a0chromatin<\/em>\u00a0composed of DNA and associated proteins (Figure\u00a03.22<\/a>). Along the chromatin threads, the DNA is wrapped around a set of\u00a0histone<\/em>\u00a0proteins. Anucleosome<\/em>\u00a0is a single, wrapped DNA-histone complex. Multiple nucleosomes along the entire molecule of DNA appear like a beaded necklace, in which the string is the DNA and the beads are the associated histones. When a cell is in the process of division, the chromatin condenses into chromosomes, so that the DNA can be safely transported to the \u201cdaughter cells.\u201d The\u00a0chromosome<\/em>\u00a0is composed of DNA and proteins; it is the condensed form of chromatin. It is estimated that humans have almost 22,000 genes distributed on 46 chromosomes.<\/p>\n

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\"This<\/div>\n<\/div>\n
Figure\u00a03.22.\u00a0DNA Macrostructure<\/strong><\/address>\n
Strands of DNA are wrapped around supporting histones. These proteins are increasingly bundled and condensed into chromatin, which is packed tightly into chromosomes when the cell is ready to divide.<\/address>\n
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