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 G 1 Phase: Cell Growth S Phase: DNA replication G 2 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