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Exam Review Reproduction The Cell Cycle • The Cell Cycle takes place in the nucleus of the cell. • The Cell Cycle is the continuous process of mitosis, cell division and interphase. Interphase • Longest phase of the cell cycle. • Cell growth and DNA replication occur during this phase. Mitosis • Mitosis results in the separation of replicated DNA into 2 identical sets of DNA, one for each new cell. • Consists of 4 phases: – Prophase, Metaphase, Anaphase and Telophase Phases of Mitosis • Prophase: Nuclear membrane disappears, genetic material becomes visible and spindle fibres form. • Metaphase: Spindle fibres line the double stranded chromosomes along the middle of the cell. • Anaphase: Spindle fibres pull double stranded chromosomes apart. • Telophase: Single stranded chromosomes reach opposite ends of the cell. Spindle fibres disappear and the nuclear membrane reforms. At this point there are 2 nuclei in one cell. Cell Division • Cytokinesis: The process of the pinching in of cytoplasm separating the cell into 2 new identical cells. Cancer and the Cell Cycle • When a cell begins to divide uncontrollably the result is cancer. • A cancerous cell becomes stuck in the cell division phase of mitosis. Since the cell does not enter interphase, DNA is not replicated, resulting in new cells being produced without all of the instructions. Meiosis • Meiosis occurs only in reproductive cells called gametes; eggs and sperm cells. • Gametes are haploid, which means they have half the number of chromosomes than regular body or somatic cells. • Somatic cells have a diploid number of chromosomes. Meiosis • The process of meiosis ensures that each gamete has only one half set of chromosomes. • Meiosis also ensures that each gamete has a different combination of chromosomes present before meiosis. Phases of Meiosis • Meiosis consists of 2 stages: Meiosis I and Meiosis II. • In Meiosis I there are 2 sets of double stranded chromosomes. • These sets match up in homologous pairs. Meiosis I • Prophase I: Single strands from each double stranded chromosome cross over and exchange parts of DNA. • Metaphase I: Homologous pairs line up along the middle of the cell. • Anaphase I: Homologous chromosomes are pulled to opposite ends of the cell. • Telophase I: Cytoplasm divides and 2 daughter cells are formed (each cell contains one from each pair of homologous chromosomes). Meiosis II • Prophase II: Nuclear membrane disappears. • Metaphase II: Chromosomes lineup along middle of cell. • Anaphase II: double stranded chromosomes are separated and chromatids are pulled to opposite ends of the cell. • Telophase II: Cytoplasm pinches in and cell divides producing 4 haploid daughter cells. DNA • DNA: Deoxyribonucleic acid • Genetic information is contained in DNA. • Chromosomes are made up of tiny DNA molecules. What does DNA do? • DNA contains the “blueprints” for the cell. • DNA gives directions to your cells to either repair damaged cell parts or to make new cells. • DNA tells the cell how to respond to changes in their environment and how to respond to messages sent by other cells. Structure of DNA • DNA is made up of many nucleotides. • A nucleotide consists of a phosphate, a sugar and a nitrogen base. • The sugar in DNA is called deoxyribose. • There are 4 nitrogen bases: – – – – Adenine Thymine Cytosine Guanine • Adenine and Thymine always pair together. • Cytosine and Guanine always pair together. Sugar Phosphate Sugars and phosphates molecules make up the sides of the ladder to give DNA its shape. The rungs of the ladder are made up of nitrogen bases. Nitrogen bases Importance of DNA • DNA removal or duplication can help scientists and individuals in many ways: – – – – – – Elimination of harmful genes Determining Paternity Forensics (Who done it?) Genetic Screening Cloning Trait Selection