Cell Division Mitosis (what's with the 'osis thing anyways)

Biology Honors Mt. Mansfield Union High School Mitosis Notes Cell Division: Mitosis (what’s with the ‘osis thing anyways?) Cell Division Cells must divide to maintain communication, transportation of material, and S.A. to volume ratio. Each dividing cell is called a mother cell The descendants are called daughter cells This process transmits DNA Cellular reproduction Three basic types of Cell Division The way that genetic information is partitioned between the daughter cells. Prokaryotic cells Membrane growth and “pinching off” Prokaryotic fission Eukaryotic cells Mitosis – two identical daughter cells Meiosis – four daughter cells with half (haploid) the number of chromosomes Prokaryotes DNA attached directly to membrane Replicated DNA are attached to slightly different points on the membrane Plasma membrane grows between these points separating the DNA A crosswall begins to form between the DNA eventually forming two identical daughter cells. Eukaryotes 1) Nuclear contents (DNA) are divided by mitosis or meiosis 2) Cell splits in two by cytokenesis Complexity of Eukaryotes 1) Eukaryotes are larger than prokayotes and contain organelles 2) Eukaryotes house much more DNA (~700x) 3) Eukaryotes contain 2-1262 chromosomes compared to a single prokaryotic “chromosome” Biology Honors Mt. Mansfield Union High School Mitosis Notes During cell division the chromosomes condense into two chromatids which are connected at the centromere. These sister chromatids are genetic duplicates. Each chromosomes of a dividing cell has a unique shape and size. Chromosome Number: Haploid vs. Diploid In eukaryotic cells chromosomes occur in pairs These two similarly shaped chromosomes are called homologues- each has the same sequence of genes along its length Most cells carry two complete sets of homologues a 2N or diploid state – one set of each homologous pair was donated by each parent during sexual reproduction Human cells have 46 chromosomes, 23 from Mom and 23 from Dad (23 pairs of homologous chromosomes) Haploid (1N) cells contain only one set of homologues – egg or sperm cells are haploid The Cell Cycle The life of a cell begins with its formation from a mother cell and ends when it divides into daughter cells or dies. Two phases of cell cycle 1) “M” or mitotic phase – may only last 30 min. to an hour a) mitosis i. chromosome separation b) cytokinesis i. divided into two daughter cells 2) interphase – majority of life cycle, preparation for cell reproduction a) G1 (Gap1) phase – follows cytokinesis and precedes DNA synthesis i. Cell grows and carries out normal metabolism ii. Organelles duplicate iii. Nerve and muscle cells do not divide and remain in G1 phase b) S (synthesis) phase i. All DNA in chromosomes is replicated ii. Chromosome duplication c) G2 (Gap2) phase – follows DNA replication and precedes mitosis i. Cell grows and prepares for mitosis Biology Honors Mt. Mansfield Union High School Mitosis Notes Phases of Mitosis Although interphase occupies most of the cell cycle mitosis is the “dance of the chromosomes” that attracts so much attention. Mitosis is a continuous process that is often broken down into four stages defined by the behavior of the chromosomes. 1) Prophase – preparing for chromosome separation a) the longest phase with a number of complex activities i. chromosome condensation each chromosome contains a single DNA molecule that is spread throughout the nucleus of an interphase cell DNA protein fibers undergo a coiling process where they are packaged into mitotic chromosomes – condensed 30,000x Formation of chromatids occurs with identical chromatids attached at the centromere ii. Spindle apparatus formation rearrangement of cytoskeleton to form spindle fibers scaffolding and chromosome pulling machine microtubules are arranged and rearranged within the cell takes place outside of the nucleus at the same time chromosomes are being compacted inside the nucleus Biology Honors Mt. Mansfield Union High School Mitosis Notes 2) Metaphase – lining up the chromosomes a) Chromosomes of dividing cells are aligned in a plane that lies at the cells equator – midway between the spindle poles b) The chromosomes and spindle apparatus are interconnected – a group of spindle fibers attaches to the kinetochore (attachment site) which is located in the centromere region of the chromosome. c) During metaphase the kinetochores are aligned and the “arms” of the chromatids extend out in various directions 3) Anaphase – separation the chromatids a) In anaphase there is a sudden synchronous separation of the kinetochores b) Separated chromatids move away from each other towards opposite spindle poles c) The daughter cell are genetically identical to each other and the mother cell 4) Telophase – producing two daughter nuclei a) Begins when the chromosomes reach the spindle poles b) Chromosomes uncoil and spindle apparatus is dismantled c) Nuclear envelopes form around each chromosome cluster Cytokinesis Division of cytoplasm Animals Indentation of cell surface during late anaphase followed by a cleavage furrow The results of contractions by a ring of microfilaments just below the cell membrane Plants Begins with the formation of a cell plate Formed by secretion vesicles containing polysaccharides produced by Golgi Bodies Biology Honors Mt. Mansfield Union High School Mitosis Notes