Cell Growth and Division

Cell Growth Limits to growth Stress on DNA Difficulty moving nutrients/wastes across membrane Ratio of surface area to volume Volume increases at a faster rate than surface area

Cell Division Before a cell becomes too large, it divides, producing 2 daughter cells Each daughter cell is an exact replica of the parent cell DNA is replicated

Cell Division 2 stages (eukaryotes) Asexual reproduction Mitosis- division of the cell nucleus Cytokinesis- division of the cytoplasm Asexual reproduction

Chromosomes Threadlike structure within the nucleus containing the genetic information (DNA) that is passed from one generation of cells to the next Cells of every organism have a specific number of chromosomes Fruit flies = 8; Humans = 46; carrots = 18

Chromosomes Chromatin- consists of DNA tightly coiled around proteins (nucleus) Chromatid- one of two identical “sister” parts of a duplicated chromosome Centromere- an area where the chromatids are attached to one another

The Cell Cycle 2 major phases Interphase Mitosis

Interphase 3 phases G1 phase= cells do most of their growing S phase= chromosomes and DNA replicated G2 phase= many of the organelles and molecules required for cell division are produced

Mitosis Divided into 4 phases Followed with Cytokinesis Prophase Metaphase Anaphase Telophase Followed with Cytokinesis Depending on cell- may last a few minutes to several days

Prophase 1st and longest phase of mitosis Events Chromosomes become visible Nucleolus disappears Nuclear envelope breaks down

Metaphase Often lasts only a few minutes Events Chromosomes line up across the center of the cell Microtubules connect the centromere of each chromosome to the two poles of the spindle

Anaphase Sister chromatids separate and move to opposite poles Anaphase ends when chromosomes stop moving

Telophase Nuclear envelope re-forms Spindle begins to break apart Nucleolus becomes visible

Cytokinesis Animal cells: Plant cells: Result? 2 new identical cells Cell membrane is drawn inward until the cytoplasm is pinched into 2 nearly equal parts Plant cells: Cell plate forms midway between the divided nuclei Cell wall begins to appear in the cell plate Result? 2 new identical cells

Controls on Cell Division Cells stop growing when they come into contact with other cells If cells are removed, the remaining cells will begin dividing again Something can turn cell division on or off

Regulating Cell Growth Cyclins- proteins that regulate the timing of the cell cycle in eukaryotic cells Internal regulators: proteins that respond to events inside the cell External regulators: proteins that respond to events outside the cell

Uncontrolled Cell Growth Cancer- disorder in which some of the body’s own cells lose the ability to control growth Cancer cells do not respond to the signals that regulate the growth of most cells