Cell Division

Learning Objective: Today, we will describe the steps of cell division.

How do these two pictures show division? Discuss with your partner two ways these show division.

ConnectionsIn math, we can use blocks and divide them into groups.

In baseball, the MLB is divided into two divisions: the American and National League.

Today, we will be looking at how cells divide and create new cells.

The Cell Cycle•Cells grow by dividing.•The cell cycle is divided into three main stages.•One “parent” cell divides to form two identical “daughter” cells.•New cells are made for various reasons:

1. Replacement of dead or dying cells2. Repair of damaged tissue3. Growth

Stage 1: Interphase

•This is the stage before cell division occurs.•During the first part of Interphase, the cell doubles in size and produces all the structures needed to carry out its functions.

Stage 1: Interphase•The cell enlarges its ER, makes new ribosomes, and produces enzymes. •The mitochondria and the chloroplasts make copies of themselves during this growth stage.

Stage 1: Interphase•The cell makes a copy of the DNA in its nucleus in a process called replication.•DNA holds all of the information that the cell needs to carry out its functions.

•At the end of replication, the cell contains two identical sets of DNA.•One set will be distributed to each daughter cell.

Stage 2: Mitosis

•There are four phases of Mitosis: Prophase, Metaphase, Anaphase, and Telophase.•During mitosis, one copy of the DNA is distributed into each of the two daughter cells.

Stage 2: MitosisPhase 1: Prophase

•Mitosis begins (the nucleus begins to divide).•Centrioles (or poles) appear and begin to move to opposite ends of the cell.•The nuclear membrane begins to break down.

Stage 2: MitosisPhase 2: Metaphase

•The Chromosomes line up across the center of the cell.

•Each chromosome attaches to a spindle fiber at its centromere, which still holds the chromatids together.

Stage 2: MitosisPhase 3: Anaphase

•One chromatid moves along the spindle fiber to one end of the cell while the other chromatid moves to the opposite end.

•The cell becomes stretched out as the opposite ends pull apart.

•The centromeres split and the two chromatids separate.

Stage 2: MitosisPhase 4: Telophase

•The chromosomes begin to stretch out and lose their rodlike appearance in the two regions at the ends of the cell.

•A new nuclear membrane forms around each region of chromosomes.

Stage 3: Cytokinesis

•The cell membrane pinches in around the middle of the cell. Eventually, the cell pinches in two.•Two daughter cells are formed. •Each has its own nucleus with identical chromosomes and about half the organelles and cytoplasm.

Stage 3: Cytokinesis

•Cytokinesis marks the end of the cell cycle.•At the end of cytokinesis, each cell enters interphase, and the cycle begins again.

Length of the cell cycle•Depends on the type of cell.•An average human cell takes about 22 hours to divide. Approximately 21 hours is spent in Interphase, while only 1 hour is spent in mitosis.•Some cells, like the human brain cells, never divide. They remain in the first part of Interphase for as long as they live.

Warm UpIn your own words, explain the process of cell division.

Which is the correct order?•Prophase, Interphase, Cytokinesis, Metaphase, Anaphase, Telophase•Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

How did you know?

Cell Division flipbookUsing notes and book pages 130-135 create a book of cell division.Please include notes in your own words for each step in cell division and draw and color a detailed picture of each step.

Closure on page ___in your notebook.1. What are the three steps of cell division?2. Which stage lasts the longest?3. Are there cells that never replicate, if so which

ones?