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Cell division functions in reproduction, growth, and repair • The ability to reproduce • cell cycle cell from its origin until its division to two. • unicellular organism - increasing the population. • Multicellular organisms repair and renew cells • The mitotic (M) phase of the cell cycle alternates with the much longer interphase . • The M phase includes mitosis and cytokinesis. • Stages of mitosis • prophase • metaphase • anaphase • telophase. Fig. 12.4 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Cell division requires the distribution of identical genetic material - DNA - to two daughter cells. • A cell’s genetic information, packaged as DNA, is called its genome. DNA duplicates, allocates the copies to opposite ends of the cell, and then splits into two daughter cells. • prokaryotes, single chromosome -DNA molecule. • Eukaryotes - chromosomes • DNA molecules are packaged into chromosomes. • Every eukaryotic species has a characteristic number of chromosomes in the nucleus. • Human somatic cells (body cells) have 46 chromosomes. • Human gametes (sperm or eggs) have 23 chromosomes, Produced by meiosis • Each eukaryotic chromosome consists of a long, linear DNA molecule. • Each chromosome has hundreds or thousands of genes, the units that specify an organism’s inherited traits. • Associated with DNA are proteins that maintain its structure and help control gene activity. • This DNA-protein complex, chromatin, is organized into a long thin fiber. • After the DNA duplication, chromatin condenses, coiling and folding to make a smaller package. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Each duplicated chromosome consists of two sister chromatids which contain identical copies of the chromosome’s DNA. • As they condense, the region where the strands connect shrinks to a narrow area, is the centromere. • Later, the sister chromatids are pulled apart and repackaged into two new nuclei at opposite ends of the parent cell. Fig. 12.3 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.29 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The sugar-phosphate backbone. • Pairs of nitrogenous bases, connect the chains with hydrogen bonds. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5 left Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5 right Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cytokinesis divides the cytoplasm: • Cytokinesis, division of the cytoplasm. • In animals, the first sign of cytokinesis (cleavage) is the appearance of a cleavage furrow Fig. 12.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Regulation of cell division. • Cultured cells normally divide until they form a single layer on the inner surface of the culture container. • If a gap is created, the cells will grow to fill the gap. Fig. 12.17 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Binary Fission Bacteria Fig. 12.10 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Humans inherit 23 chromosomes from each parent • The fertilized egg underwent trillions of cycles of mitosis and cytokinesis to develop a human. • These processes continue every day to replace dead and damaged cell - produce clones • In contrast, gametes (eggs or sperm) are produced only in gonads (ovaries or testes) In humans, meiosis reduces the number from 46 to 23. • Fertilization fuses two gametes together and doubles the number of chromosomes to 46 again. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings