Cell Division

Objectives1. Describe the cell cycle.2. Describe the events in each stage of mitosis.3. Explain cancer as a disease of the cell cycle.

Pg 240-252

Think! Think!! Think!!!

Does a living thing grow larger because it increases the size of its cells or because it produces more cells?

Think! Think!! Think!!!

Living things grow because they produce more cells. There is a limit to the size that cells can grow. The DNA that is in the nucleus of each cell is like the library of a small town. When the town is small, there are enough books for the residents to share. If the town population were to increase, there would be a shortage of books. So instead of growing larger, cells must reproduce.

Cell Division

Cell Division – the process by which a cell divides into two new identical daughter cells

Before cell division, the DNA of the cell is copied, so each daughter cell gets a copy.

DNA – (deoxyribonucleic acid) the large molecule in the nucleus of each cell that carries genetic information

Chromatin

Chromatin - DNA in the nucleus that looks like spread out “strings” when the cell is not dividing

Chromosomes

Chromosomes – condensed chromatin visible in the nucleus when the cell is dividing

Humans have 46 chromosomes or 23 pairs.

Chromosomes

Before cell division, each chromosome is duplicated. The identical chromosomes attach to each other.Sister Chromatids –

two identical chromosomesattached to each other

Centromere – the place that the sister chromatids are attached to each other

The Cell Cycle

Interphase G1 – “G for Grow” the cell

size increases S – “S for DNA Synthesis”

the chromosomes are duplicated

G2 – centrioles and other organelles required for cell

division are madeMitosis – the duplicated chromosomes separate, has four phasesCytokinesis – the cell physically splits in two

Cancer: A Disease of the Cell Cycle

Cancer – a disorder in which some of the body’s cells divide uncontrollably.

The cells that continue to divide cause masses called tumors.

Causes can be tobacco, UV radiation, or viruses.

Mitosis

Prophase – chromatin condenses into sister chromatids, centrioles separate, spindle forms, nuclear envelope breaks downMetaphase – sister chromatids line up across middle of cell, each is connected to a spindle fiber at its centromereAnaphase – sister chromatids separate and move to opposite sides of the cellTelophase – sister chromatids lose their shape and become chromatin, two new nuclear envelopes form

http://www.rattlerscience.com/life/classes/preapbio/documents/Unit%203/chapter10/cell_cycle.swf

http://bio.rutgers.edu/~gb101/lab2_mitosis/graphics/aavideo.mov