Cell Growth & Division

Limits to cell growth 10-1 Cell Growth

DNA overload When a cell is small, its DNA is able to meet all of the cell’s needs. As the cell grows it produces more organelles, but the DNA is not replicated and it cannot meet the cell’s needs Cell Growth

Exchanging materials The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume. As the cell grows it becomes more difficult for it to get rid of wastes and to get food and oxygen into the cell Cell Growth

Ratio of surface area to volume Imagine a cell that is shaped like a cube. The surface area of a cell would be equal to length x width x number of sides(6) of a cell. The volume of the cell would be equal to length x width x height of the cell. The volume of the cell increases more rapidly than the surface area Cell Growth

Example Cell size Surface area volume Ratio of surface area to volume 10-1 Cell Growth

Division of the cell The process by which a cell divides into two new daughter cells is called cell division. Before the cell divides, it replicates all of its DNA. This process reduces cell volume and solves the DNA overload problem. Division of the cell Division of the cell – Cell growthCell growth 10-1 Cell Growth

10-2 Cell Division

Chromosomes The information that is passed from one generation to the next is carried by chromosomes. They are made up of DNA and proteins A chromosome consists of two sister chromatids Cell Division

Cell cycle The G1, S and G2 phases are part of the interphase in the cell cycle. The cell cycle is divided into four phases, which are: G1 phase: the cell grows S phase: DNA is replicated G2 phase: The cell prepares to divide M phase: mitosis and cytokinesis 10-2 Cell Division

Back Prophase Metaphase Anaphase Telophase Cytokinesis Cell Cycle 10-2 Cell Division

Prophase During prophase, the chromosomes become visible. The centrioles take positions in opposite sides of the cell and form the spindle Cell Division

Metaphase During metaphase, the chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the two poles of the spindle Cell Division

Anaphase During Anaphase, the centromeres that joined the sister chromatids split becoming individual chromosomes Cell Division

Telophase The chromosomes move to opposite sides of the cell and a nuclear envelope forms around each group of chromosomes Cell Division

Cytokinesis The process in which the cytoplasm separates, forming completely the two new daughter cells. It usually occurs about the same time as Telophase. This occurs different in plants and in animals Cell Division

Animals The cell membrane is drawn inwards until the cytoplasm is pinched into two nearly equal parts. Each part contains its own nucleus and cytoplasmic organelles Cell Division

Plants A structure known as the cell plate forms midway between the divided nuclei. The cell plate gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate. A structure known as the cell plate forms midway between the divided nuclei. The cell plate gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate Cell Division

Regulating the Cell Cycle 10-3 Regulating the Cell Cycle

Cells grow until they touch other cells If center cells are removed, cells near the space will start to grow again. SHOWS: Cell division genes can be turned on and off 10-3 Regulating the Cell Cycle

In early 1980’s scientists discovered a protein in dividing cells that caused a _________________to form in _______________ cells CELL CYCLE REGULATORS Mitotic spindle NON-dividing 10-3 Regulating the Cell Cycle

Levels of this protein rose and fell with the cell cycle so it was named __________ because it seemed to control the cell cycle. A whole family of CYCLINS have since been discovered that regulate the _____________________ in EUKARYOTIC CELLS CELL CYCLE REGULATORS CYCLIN TIMING of CELL CYCLE 10-3 Regulating the Cell Cycle

______________ REGULATORS Proteins that respond to events inside the cell. Allow cell cycle to proceed only if certain processes have happened EX: Cell can’t enter mitosis until all the chromosomes have been copied OTHER REGULATORS INTERNAL 10-3 Regulating the Cell Cycle

______________ REGULATORS Proteins that respond to events outside the cell. Signals tell cell to speed up or slow down the cell cycle EX: Growth factors stimulate cells to divide Especially important during wound healing and embryo development OTHER REGULATORS EXTERNAL 10-3 Regulating the Cell Cycle

Molecules on the surface of neighboring cells act as signals to slow down or stop the cell’s cycle. These signals prevent excessive growth and keep tissues from disrupting each other. EXTERNAL REGULATORS 10-3 Regulating the Cell Cycle

SEM Image by: Riedell 10-3 Regulating the Cell Cycle

Cancer cells don’t stop when they touch nearby cells... they just keep growing! That’s what makes a tumor. NO CONTACT INHIBITION Regulating the Cell Cycle

Carcinogens 10-3 Regulating the Cell Cycle

CELL CYCLE p Regulating the Cell Cycle