Cell Growth and Division Limits to growth Cell

Cell Growth and Division

• Limits to growth Cell 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) – 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 – G 1 phase= cells do most of their growing – S phase= chromosomes and DNA replicated – G 2 phase= many of the organelles and molecules required for cell division are produced

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

Prophase • 1 st 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 reforms • Spindle begins to break apart • Nucleolus becomes visible

Cytokinesis • Animal 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