Cell Division

The Cell Cycle and Meiosis

Somatic Cellular Reproduction:

The Cell Cycle and Mitosis

Cells that make up the “body”.

Somatic Cells

Why do Somatic Cells DivideReproduction

Growth

Repair

Development

Surface : Volume

Maintain chromosome number

Structures that contain the genetic material

Chromosomes

ChromosomesComposed of chromatin and proteins

Each Chromosome (after the S phase) contains two identical parts called “sister chromatids” attached at a centromere (referred to as “double stranded”)

• Interphase and Mitosis• The cycle of growth and division in all cells

The Cell Cycle

Interphase

Prophase

Metaphase

• Either of two submicroscopic attachment points for chromosomal microtubules, present on each centromere during the process of cell division

Kinetochore

Mitotic Spindle made of microtubules

• Several microtubules joined together create structures known as spindle fibers which guide chromosomes during mitosis.

Spindle Fibers

Spindle Fibers

Spindle Fibers

Anaphase

Telophase

Cytokinesis

Identify the Stages of Mitosis

1 2 3

4 5

Cell Cycle Regulation

Checkpoints during each phase

Signals registered at the checkpoints report the status of various cellular conditions

(e.g., Is the environment

favorable? Is the cell big enough? Is all DNA

replicated?

Molecular protein clocks that regulate the activities of the cell cycle in a particular order

Levels controlled by genes:

Proto-Onco Genes Stimulate

Tumor Supressor Genes Inhibit (p53 is a common example)

p53 is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is severe this protein can cause apoptosis (cell death).

Cyclin Dependent Kinases

Cell Growth and Division Also Regulated By External Factors:Density

Growth Factors

Cancer

Cancer cells do not

respond normally to the body's

control mechanisms.

They divide excessively, invade other tissues and, if unchecked, can kill the

whole organism.

Abnormal cells which have

escaped normal cell-

cycle controls are the

products of mutated or transformed normal cells.

A p53 mutation is the most frequent mutation leading to

cancer because it prevents

apoptosis.

Malignant Tumors and Metastasis

Meiosis

Why Meiosis?

Sexual reproduction

Reduction of chromosome number

Genetic recombinati

on

Prophase I

Metaphase I

Anaphase I

Telophase I

Meiosis I

Prophase II

Metaphase II

Anaphase II

Telophase II

Meiosis II

Crossing-Over

Nondisjunction