If cancer is uncontrolled If cancer is uncontrolled cell division…why would a cell division…why would a

cell divide in the first cell divide in the first place? place?

Brainstorm a list of reasons a cell would divide.

Why would a cell divide? Why would a cell divide?

DNA “overload”Trouble exchanging materialsRepair an injuryReplace old worn out cellsAsexual reproductionOrganism = growth

The Cell CycleThe Cell CycleThe series of events that cells go through as they

grow and divide.

http://wise.berkeley.edu/webapp/teacher/index.html

Where does cell division occur? Where does cell division occur?

Most cells are able to divide…

But some cannot, like:

Most nerve cellsBrain cellsHeart cellsBlood cells

Cut out your cells and Cut out your cells and place them in place them in

chronological order. chronological order. Glue them in your notebook once

you have approval.

What is the end product of What is the end product of mitosis? mitosis?

Steps of the cell cycleSteps of the cell cycle

Step One: copy the DNAStep One: copy the DNA

Stop and think: why would it be important to do this each time?

Step Two: Split the DNA equally Step Two: Split the DNA equally between the 2 cellsbetween the 2 cells

Step three: Split the cell’s Step three: Split the cell’s contentscontents

Life Cycle of a CellLife Cycle of a Cell

Before a growing cell becomes too large it divides

The division results in two essentially identical cells called “daughter cells”.

Prior to division the cell replicates all of its DNA.

Replication solves the problem of information storage, each daughter cell receives its own genetic information

Why would it be important that the cell copies itself before dividing???

What would happen if a cell split into two without copying itself? Would both sides survive?

Phases of MitosisPhases of Mitosis

InterphaseInterphase

In interphase the DNA in the nucleus is in a loose stringy form called chromatin

DNA replication takes place, copying itself to get ready for mitosis

ProphaseProphase

During prophase chromosomes become visible, centrioles take position on opposite sides of the nucleus

Nucleus disappears and the nuclear envelope breaks down

MetaphaseMetaphase

Chromosomes begin to line up across the center of the cell

Each chromosome is now connected to a spindle fiber at its centromere

AnaphaseAnaphase

The centromeres that join the sister chromotids separate creating two individual chromosomes

Chromosomes continue to move until the have separated into two groups near the poles of the spindle

TelophaseTelophase

The chromosomes gather at opposite ends of the cell

Chromosomes begin to lose their distinct shape

Two new nuclear membranes form

CytokinesisCytokinesis

Cytokinesis is the division of the cytoplasm

Occurs at same time as telophase (not a different step in mitosis)

Done a little different in plant and animal cells

Prophase Metaphase Anaphase Telophase