Chapter 10 Cell Growth and Division

Cell Reproduction Why do cells Reproduce? To help tissues and organs grow and to replace dead or damaged cells Cells need to divide to limit their size because….  Their ability to exchange substances is limited by their surface area to volume ratio. Small cell exchange substances more efficiently than large cells.  Large cells need to make more protein to support cell functions. DNA can not be copied quickly enough in large cells to support their needs.

Chromosomes DNA is organized and packaged into structures call Chromosomes in eukaryotic cells. Prokaryotic cells have a loop of DNA. Chromosomes Are made of Chromatin Which is made of Nucleosomes Which are DNA wound around Histones

DNA Nucleosomes (DNA wound around histones) Chromatin Chromosome

UNPACKED (before cell division) PACKED During cell division nucleus Condensed package Chromatin

Chromosome

Preparing for Cell Division  All new cell come from the division of pre- existing cells  Before a cell divides, it must copy its DNA so that the original cell and its copy (daughter cell) each has the DNA it needs to carry out cell functions.

Cell Cycle The cell cycle is a repeating sequence of cellular growth and division during the life of a cell Interphase G 1 S G 2 Mitosis Prophase Metaphase Anaphase Telophase

Interphase Cells that divide often spend less time in interphase, while those that seldom divide spend a long time in interphase. Which cells, brain or bone, spend a longer time in interphase?

Interphase  G1 (Growth) Cell rapidly grows and makes more organelles Cells that don’t divide remain at this stage  S (DNA synthesis) A cell’s DNA is copied  G2 (Growth and preparation for division) Cells continue to grow and develop special structures (microtubules or spindle fibers) for cell division

Mitosis The process of dividing a cell into two daughter nuclei Following mitosis a process called cytokinesis occurs in which the organelles and cytoplasm in the cell are separated creating two new daughter cells.

Prophase  Chromosomes begin to condense and become visible under a light microscope.  The nuclear membrane breaks down.  The spindle forms

Metaphase Chromosomes line up at the cell’s equator. Spindle fibers form a link between the centromeres of the chromosome and the poles of the cell.

Anaphase  The spindle fibers shorten  Sister chromatids move toward opposite poles of the cell

Telophase  A nuclear envelope forms around the chromosomes at each pole  Chromosomes uncoil  Spindle fibers breakdown and disappear

Cytokinesis  Cell membrane grows into the center of the cell  Nuclear membrane forms around the two new nuclei

Identify the Stages

Cell Cycle Regulation Cell growth and division depend on protein signals and other environmental agents. Other things that regulate cell growth and division:  Signals from surrounding cells and tissues  Availability of nutrients

Checkpoints  G 1 Checkpoint  Before a cell can go into the S phase (DNA replication) The health and size of the cell is evaluated. If conditions are not favorable, the cell goes into a resting period.  G 2 Checkpoint  Before a cell can begin mitosis, its DNA needs to be examined for mistakes. Enzymes correct mistakes so that each daughter cell produced in mitosis contain the same DNA. Cell size is also double checked.

Checkpoints cont.  Mitosis checkpoint  During metaphase, the cell checks to see if the chromosomes are properly attached to the spindle fibers.

Cancer Uncontrolled cell growth and division can result in masses of cells that invade and destroy healthy tissues.  Cancer results from the loss of control of cell cycle regulation  Benign tumors or malignant tumors may occur.  Chemotherapy or radiation is used to kill cancer cells  Some cancers can be prevented by avoiding those things known to cause cancer.