Chapter 10 Cell Growth and Division

Think about it…  How would you describe the process by which a multicellular organism increases its size?  Why do cells stay small?

Liver cell completes cell division – Magnification 11,500x

Limits to Cell Growth  Two reasons why cells can’t grow indefinitely and must divide:  DNA overload  Exchange of materials

DNA Overload  When the cell is small, the information stored in that DNA is able to meet all of the cell’s needs  If the cell grows too large, the DNA cannot produce enough proteins to supply the cell

Exchanging Materials  The rate at which food, oxygen, water, and wastes are moved in and out of the cell is dependent on the surface area of the cell. Surface area – the cell membrane

Exchanging Materials  The rate at which food, oxygen and water are used and waste is produced depends on the cell’s volume.

Exchanging Materials  Ratio of Surface Area to Volume  Ratio of Surface Area to Volume  As the length of a cell increases, its volume increases faster than the surface area.  The decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.

The surface area must be must allow sufficient exchange to support the contents of the cell!

Calculate the following of a cubic cell measuring 4cm on each side: Surface Area Volume Ratio of Surface Area to Volume:

Division of the Cell  Before it becomes too large, a growing cell divides forming two ‘daughter’ cells called cell division  Before cell division occurs, the cell replicates all of its DNA  Each daughter cell gets one complete set of genetic info

10.2 Cell Division  In eukaryotic cells, cell division occurs in two main stages: 1.Mitosis – division of the cell nucleus 2.Cytokinesis – division of cell cytoplasm

Chromosomes  Genetic information is passed from one generation to the next on chromosomes (made of DNA).  Chromosomes are not visible in most cells except during cell division (other times the DNA is in the chromatin state)  Before cell division, the DNA condenses into compact structures, chromosomes  Each chromosome is duplicated, or copied.

Chromosomes  Once copied, each chromosome consists of two identical “sister” chromatids.  Chromatids are attached at the centromere  When the cell divides, the sister chromatids separate and each new cell receives one Centromere Sister chromatids

The Cell Cycle  The cell cycle is the series of events that cells go through as they grow and divide.  During the cell cycle:  a cell grows  prepares for division  divides to form two daughter cells, each of which begins the cycle again  Interphase is the period of growth that occurs between cell divisions.

The Cell Cycle  The cell cycle consists of four phases:  G 1 (First Gap Phase)  S Phase  G 2 (Second Gap Phase)  M Phase

Events of the Cell Cycle  During G 1, the cell  increases in size  synthesizes new proteins and organelles

Events of the Cell Cycle  During the S phase,  chromosomes are replicated  DNA synthesis takes place  Once a cell enters the S phase, it usually completes the rest of the cell cycle.

Events of the Cell Cycle  The G 2 Phase (Second Gap Phase)  organelles and molecules required for cell division are produced  Once G 2 is complete, the cell is ready to start the M phase—Mitosis

Cell Cycle Events of the Cell Cycle

Mitosis  Biologists divide the events of mitosis into four phases:  Prophase  Metaphase  Anaphase  Telophase

Mitosis

Section 10-2 Prophase Spindle forming Chromosomes (paired chromatids) Centromere Mitosis  Prophase

Mitosis  Prophase is the first and longest phase of mitosis.  The centrioles separate and take up positions on opposite sides of the nucleus.  The spindle, a microtubule structure, forms between the centrioles  The nuclear envelope breaks down. Spindle forming Centromere Chromosomes (paired chromatids)

Centriole Spindle Mitosis Click to Continue Metaphase  Metaphase

Mitosis  The second phase The chromosomes line up across the center of the cell.  Microtubules connect the centromere of each chromosome to the poles of the spindle. Centriole Spindle

Individual chromosomes Anaphase Mitosis  Anaphase

Mitosis  The third phase of mitosis.  The sister chromatids separate into individual chromosomes.  The chromosomes continue to move until they have separated into two groups. Individual chromosomes

Nuclear envelope reforming Telophase Mitosis  Telophase

Mitosis  Telophase is the fourth and final phase of mitosis.  Chromosomes gather at opposite ends of the cell and lose their distinct shape.  A new nuclear envelope forms around each cluster of chromosomes.  Spindle breaks apart and the nucleolus reappears.

Cytokinesis Cytokinesis  Cytokinesis

Cytokinesis  Not a phase of mitosis  During cytokinesis, the cell membrane pinches in and the cytoplasm is split between the two cells.  Each daughter cell has an identical set of duplicate chromosomes

Cytokinesis in Plants  In plants, a structure known as the cell plate forms midway between the divided nuclei. Cell wall Cell plate

Cytokinesis in Plants  The cell plate gradually develops into a separating membrane.  A cell wall then begins to appear in the cell plate.

Cells in Mitosis ml ml Things to look: Shape of Cell Chromosomes Presence of a nucleus Where the chromosomes are in the cell If there is a division forming between cells

Mitosis Animations   9QB0 9QB0 9QB0  chem.swf chem.swf chem.swf  mitosis.html mitosis.html mitosis.html  s/cell_cycle/cells3.html s/cell_cycle/cells3.html s/cell_cycle/cells3.html

Controls on Cell Division  Normal cells will reproduce until they come into contact with other cells.  When cells come into contact with other cells, they respond by not growing.  This shows that cell growth and division can be turned on and off.

Cell Cycle Regulators  The cell cycle is regulated by a specific protein called cyclin  The amount of this protein in the cell rises and falls in time with the cell cycle

Internal Regulators Internal Regulators  Proteins that respond to events inside the cell are called internal regulators.  Internal regulators allow the cell cycle to proceed only when certain processes have happened inside the cell.

External Regulators External Regulators  Proteins that respond to events outside the cell are called external regulators.  External regulators direct cells to speed up or slow down the cell cycle.

Uncontrolled Cell Growth  Cancer is a disorder when cells lose the ability to control growth.  Cancer cells do not respond to the signals that regulate the growth of most cells.  Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.  Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.

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