Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cell Division and Reproduction • Before a cell becomes too large, it divides forming 2 “daughter” cells. This process is called cell division. • It keeps the large SA:V and keeps the cell from having “information overload” by coping its genetic material Reproduction • Asexual: the production of genetically identical offspring from a single parent Ex: bacteria, hydra, some plants • Sexual: offspring produced by sexual reproduction inherit some of their genetic information by each parent Ex: most animals and plants Cell Cycle • Chromosomes- Genetic information (DNA) bundled in to packages – In most prokaryotes, a single chromosome holds most of the organism's DNA • Eukaryotes usually have much more DNA • Chromosomes in eukaryotic cells form a close association with histones, a type of protein. • Chromosome + histone= chromatin • Centrioles- organelle used to pull apart chromosomes • Spindle fibers- fibers used to pull apart chromosomes • Cell cycle: cells grow, prepare for division and divides to form 2 daughter cells • Prokaryotic Cell Cycle: Binary Fission (asexual) – DNA duplicates, cell membrane indents, cell divides, 2 new cells with genetically identical organisms are produced Eukaryotic Cell Cycle • Interphase: Resting stage of cycle; DNA is copied Interphase • G1 Phase: Cell Growth • S Phase: DNA replication • G2 Phase: Preparation for mitosis • M Phase: follows interphase, produces 2 daughter cells Prophase • The DNA condenses into visible chromosomes • The nuclear envelope disappears • Spindle fibers form Metaphase • Chromosomes align at the center of the cell • Spindle fibers connect the centromere of each chromosome to the two poles of the spindle Anaphase • The sister chromatids pulled apart by spindle Telophase • Chromatids are at opposite ends of cell • Nuclear envelope reforms • Spindle disappears, chromosomes disappear Cytokinesis • The cytoplasm divides into two cells. Each cell is identical to the parent cell • Mitosis- the nucleus divides • Cytokinesis- the cytoplasm divides • Cytokinesis in plant cells: cell wall is too ridged to bend so a cell plate forms and later becomes the cell membranes followed by the new cell wall Regulating the Cell Cycle • The cell cycle is controlled by regulator proteins both inside and outside the cell • Cyclin: a protein that regulates the cell cycle • Internal regulators: respond to events within the cell – Ex: proteins that make sure a cell does not enter mitosis until its chromosomes have replicated • External regulators: respond to events outside the cell – Ex: Growth factors stimulate the growth and division of cells • Apoptosis: Programmed Cell Death Cancer: uncontrolled cell growth • Cancer cells do not respond to signals that regulate the growth of most cells. • Could be caused by defects in the genes that regulate cell growth and divisions • Sources of such defects include: smoking or chewing tobacco, radiation exposure, other defective genes