Chapter 2, Section 5 Cell Division Thursday, October 22, 2009 Pages

Objectives Understand the events that take place during the three stages of the cell cycle. Understand the role of DNA replication. Know the role of nitrogen bases.

Vocabulary Words Cell Cycle Interphase Replication Mitosis Chromosomes Chromatid Cytokinesis Daughter cells Centromere

The Cell Cycle The cell cycle is a sequence of growth and division that cells undergo. The cell cycle is divided into three main stages.

Interphase Interphase is the first stage of the cell cycle. The cell grows to its mature size. A copy of the DNA is made. The cell prepares to divide into two cells.

Mitosis Mitosis occurs in 4 phases. Prophase Metaphase Anaphase Telophase

Prophase The threadlike chromatin in the nucleus begins to condense into tiny rods. Doubled rods of condensed chromatin is called chromosome. Each “leg” of the chromosome is called a chromatid. The centromere holds the two strands together.

Metaphase Second stage of mitosis. The chromosomes line up in the center and are attached to the spindle fibers.

Anaphase Centromeres split and the chromatids separate. Chromatids move toward opposite poles along the spindle fiber. A complete set of chromosomes has assembled at each pole at the end of anaphase.

Telophase Nuclei begin to form at opposite poles. Chromatin fibers of chromosomes uncoil. DNA on one cell have been divided equally into two. Telophase ends mitosis.

Cytokinesis Completes the process of cell division. Cytoplasm divides and distributes the organelles into each of the two new cells. Each daughter cell has the same number of chromosomes as the original parent cell. At the end of cytokinesis, each cell enters interphase and the cycle begins again.

Length of Cell Cycle The time it takes a cell to go through one cell cycle depends on the type of the cell. The length of each stage in the cell cycle also varies.

DNA Ladder The ladder is made up of alternating sugar and phosphate molecules. Each rung is made up of a pair of molecules called nitrogen bases. 4 kinds of nitrogen bases: Adenine, thymine, guanine, and cytosine. A-T and G-C

The Replication Process DNA replication begins when the 2 sides of the DNA molecule unwind and separate. The nitrogen bases then pair up on each half of the DNA molecule. The order will be identical to that of the original DNA molecule.

Homework Workbook Chapter 2, Section 5 -- due 10/26.