Describe the Process of Cell Division in Prokaryotic Cells
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The Cell Cycle Objective # 1 In this topic we will examine the cell cycle, the series of changes that a cell Compare the amount and goes through from one division to the organization of genetic material in next. prokaryotic cells with the amount We will pay particular attention to how and organization of genetic the genetic material is passed on from material in eukaryotic cells. parent cell to daughter cells during the cell cycle. 1 2 Objective 1 Objective 1 An average eukaryotic cell has about 1,000 times more DNA then an The DNA in a eukaryotic cell is average prokaryotic cell. organized into several linear Prokaryotes have a single, circular chromosomes. Each chromosome DNA molecule. It is sometimes called normally contains one DNA molecule “naked” because the DNA is not which is combined with special combined with proteins. proteins called histones. 3 4 Objective 1 Objective # 2 DNA Prokaryotes Eukaryotes structure single, naked, many linear circular DNA chromosomes, Describe the process of cell molecule each made of 1 DNA molecule division in prokaryotic cells. joined with protein location in an area of the inside a cytoplasm called membrane-bound the nucleoid nucleus 5 6 1 Objective 2 Objective 2 Prokaryotes use a type of cell 3) Finally, the cytoplasm divides in half, division called binary fission: producing 2 daughter cells which 1) First, the single, circular DNA each have one copy of the original molecule replicates, producing two DNA molecule. Therefore, the 2 identical copies of the original. new cells are genetically identical to 2) Next, the 2 DNA molecules move each other and to the original cell: to opposite ends of the cell. 7 8 Objective 2 Objective # 3 Describe the structure of both unduplicated and duplicated eukaryotic chromosomes; and distinguish between chromosome, chromatid, centromere, and chromatin. 9 10 Objective 3 Objective 3 Eukaryotic chromosomes are made How can such long molecules fit inside of chromatin, a complex of DNA a microscopic nucleus? and protein. ¾Every 200 nucleotide pairs, the DNA Each unduplicated chromosome wraps twice around a group of 8 histone contains one DNA molecule, which proteins to form a nucleosome. may be several inches long. ¾Higher order coiling and supercoiling also help condense and package the chromatin inside the nucleus: 11 12 2 Objective 3 Objective 3 For much of the cell cycle, most of the chromatin is loosely coiled. During this time, the individual chromosomes cannot be seen inside the nucleus. 13 14 Objective 3, Eukaryotic Nucleus Objective 3 Prior to cell division each chromosome duplicates itself. All the duplicated chromosomes then condense into short rod-like structures that can be seen and counted under the microscope: 15 16 Objective 3 Objective 3 Because of duplication, each condensed chromosome consists of 2 identical chromatids joined by a centromere. Each duplicated chromosome contains 2 identical DNA molecules (unless a mutation occurred during duplication), one in each chromatid: 17 18 3 Objective 3 Objective 3 The centromere is a constricted point on the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores. Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division. 19 20 Objective 3 Objective # 4 Explain what karyotypes are and how they are useful. 21 22 Objective 4 Objective 4 The particular array of chromosomes in a eukaryotic cell is called its karyotype. To examine a karyotype, the chromosomes are photographed when they are highly condensed, then photos of the individual chromosomes are cut out and arranged in order of decreasing size: 23 24 4 Objective 4 Objective # 5 Karyotypes are used to study the Distinguish between a haploid number and structure of the chromosomes present in a cell. cell and a diploid cell. Distinguish between identical They can also be used to detect chromosomal abnormalities that may chromosomes, homologous be associated with specific genetic chromosomes, and non- traits or defects. homologous chromosomes. 25 26 Objective 5 Objective 5 In eukaryotes, every species requires a Cells that contain 1 complete set of specific number of chromosomes to chromosomes are called haploid. code for all the polypeptides produced n or N represents the number of by the organism. These chromosomes chromosomes in a haploid cell. make up 1 complete set. Cells that contain 2 complete sets of Each chromosome in a set controls chromosomes are called diploid. the production of a different group of 2n or 2N represents the number of polypeptides. chromosomes in a diploid cell. 27 28 Objective 5 Objective 5 For example, 23 different We will use different shapes to chromosomes are needed to code for represent the different chromosomes all the polypeptides produced by that make up a set, and different colors humans. to represent different sets of chromosomes. Therefore, in humans: N=23 2N = 46 29 30 5 Objective 5 Objective 5 Unduplicated Chromosomes Duplicated Chromosomes Haploid Cell, N = 3 Diploid Cell, 2N = 6 Haploid Cell, N = 3 Diploid Cell, 2N = 6 31 32 Objective 5 Objective 5 In a diploid cell, the chromosomes However, homologous chromosomes are occur in pairs. The 2 members of each not identical because they may code for pair are called homologous different forms of each trait: chromosomes or homologues. Red eyes Short wings Tan body Under the microscope, homologous chromosomes look identical. In addition, because they code for the same polypeptides, they control the White eyes Long wings Tan body same traits. 33 34 Objective 5 Objective 5 Identical chromosomes: Homologous chromosomes: ¾Look the same under the ¾Look the same under the microscope (have microscope (have the same shape the same shape but different colors on our and color on our diagrams) diagrams) ¾Control the same traits ¾Control the same traits ¾May code for different forms of each trait ¾Code for the same form of each trait ¾Independent origin - each was inherited from ¾Common origin – both descended a different parent from the same original chromosome 35 36 6 Objective 5 Objective 5 Non-homologous chromosomes: Duplicated Chromosomes ¾Look different under the microscope (have different shapes on our diagrams) ¾Control different traits Haploid Cell, N = 3 Diploid Cell, 2N = 6 37 38 Objective # 6 Objective 6 Gene – a section of a DNA molecule that contains the code for making one Define and be able to use the polypeptide. following terms correctly: gene, Gene locus –the location of a gene gene locus, and allele. along the length of a chromosome Alleles – genes that can occupy the same gene locus (on different chromosomes) 39 40 Objective 6 Objective # 7 Homologous Chromosomes Red eyes Short wings Tan body Identify the stages of the eukaryotic cell cycle, and describe the events of each stage. White eyes Long wings Tan body 41 42 7 Objective 7 Objective 7 The cell cycle refers to the sequence of Interphase is subdivided into 3 stages: events that occur as a cell grows and ¾ G1 is the primary growth phase of the divides. It is divided into 2 main stages: cell cycle ¾ Interphase – chromosomes are not ¾ S is when the cell synthesizes a copy of visible. Involves cell growth and its chromosomes (DNA duplication). duplication of the genetic material. ¾ G2 is the second growth phase, during ¾ Cell division – includes division of the which preparations are made for cell duplicated chromosomes (mitosis) and division. division of the cytoplasm (cytokinesis). 43 44 Objective 7 Objective 7 Mitosis is subdivided into 4 stages: ¾Prophase ¾Metaphase ¾Anaphase ¾Telophase 45 46 Objective # 8 Objective 8 Mitosis: ¾ some haploid and some diploid cells List, describe, diagram, and may divide by mitosis. identify the stages of mitosis. ¾ each new cell receives one copy of every chromosome that was present in the original cell. ¾ produces 2 new cells that are both genetically identical to the original cell. 47 48 8 Objective 8, Mitosis in a Diploid Cell (2N=6) Objective 8, Mitosis in a Haploid Cell (N=3) DNA duplication during DNA duplication during interphase interphase Mitosis Mitosis 49 50 Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6) Prophase: ¾ nuclear membrane disintegrates ¾ nucleolus disappears ¾ duplicated chromosomes condense ¾ mitotic spindle begins to form ¾ kinetochores begin to mature and attach to mitotic spindle Prophase 51 52 Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6) Metaphase: ¾kinetochores attach duplicated chromosomes to mitotic spindle ¾chromosomes line up, in single file, along metaphase plate at equator of cell Metaphase 53 54 9 Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6) Kinetochore Anaphase: Microtubule ¾ centromeres split so that each duplicated chromosome becomes 2 identical, unduplicated chromosomes ¾ kinetochore microtubules shorten, pulling identical chromosomes to opposite poles ¾ polar microtubules elongate preparing Polar Microtubule cell for cytokinesis 55 Anaphase 56 Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6) Telophase: ¾ chromosomes reach poles of cell ¾ kinetochores disappear ¾ polar microtubules continue to elongate, preparing cell for cytokinesis ¾ nuclear membrane reforms ¾ nucleolus reappears ¾ chromosomes decondense Telophase 57 58 Objective 8, Mitosis in a Haploid Cell (N=3) Objective 8, Mitosis in a Haploid Cell (N=3) Metaphase Prophase 59 60 10 Objective 8, Mitosis in a Haploid Cell (N=3) Objective 8, Mitosis in a Haploid Cell (N=3) Kinetochore Microtubule Polar Microtubule Anaphase 61 Telophase 62 Objective # 9 Objective 9 Cytokinesis refers to division of the cytoplasm during cell division, while Describe the process of mitosis refers to division of the genetic cytokinesis and distinguish material (chromosomes). between mitosis and Although cytokinesis generally follows cytokinesis. mitosis, this isn’t always the case. 63 64 Objective 9 Objective 9 In animal cells and other eukaryotic cells that lack a cell wall, cytokinesis is achieved by means of a constricting belt of actin filaments.