Chapter 9: Chromosomes and Mitosis

p. 198 - 207

Review of Important Terms:

Gene - segment of DNA that codes for a protein

Chromosome - DNA + proteins, each contains thousands of genes, visible in cell during cell division

Mitosis - the division of the cell nucleus resulting in two daughter cells; consists of 4 phases

Genes

DNA is organized into genesEach chromosome may contain hundreds - thousands of genesHumans have 35,000 - 40,000 genes that code for proteins

Chromosomes

located in cell nucleusmade of chromatin  - a complex material consisting of proteins  and DNA - long, thin threads When a cell is not dividing, chromosomes are present but in an unraveled formDuring division, chromatin fibers condense into chromosome form

Chromosomes

Every species has a specific number of chromosomes present in the nuclei of body cells

It is not the number of chromosomes that makes the species unique, but the information specified by the genes

Humans have _____ chromosomesMost plants and animals have between ____ and ____ chromosomes

The Cell Cycle

Cell cycle - sequence of cell growth and divisionDo all cells divide?  - Types of cells that do not divide: - nerve - skeletal muscle - red blood cells If cells divide, undergo mitosis

Cell Cycle

represented by a circlegeneration time - period of one division to the beginning of the next - can vary widely Divison involves 2 main processes: - Mitosis - Cytokinesis

Mitosis.mpg

Cell Cycle

Interphasemost of the cell's lifeno cell divisionG1 - no DNA synthesis occurs, growth period, longest stageS - DNA replication G2 - shortest of the 3 phases of interphase, completion marks the beginning of mitosis, 2nd phase of growth

4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

The Stages of Mitosis.mpg

Mitosis

Cell Cycle

Longest phase: 50-60% of total time in mitosisThe chromosomes become visibleCentrioles - separate and take up positions on opposite sides of the nucleusSpindle begins to form - its job is to help separate the chromosomes Nuclear envelope breaks down

Prophase

Only lasts a few minutesChromosomes line up across the center of the cellCentromere of each chromosome is attached to the spindle

Metaphase

Centromeres split Sister chromatids separate and become individual chromosomesChromosomes move to opposite ends of the cell

Anaphase

Final stage of mitosisChromosomes begin to disperse into a tangle of dense materialNuclear envelope reforms around each cluster of chromosomesSpindle breaks apartNucleolus becomes visible in each daughter nucleus

Telophase

Cell Cycle

Cytokinesisformation of 2 separate daughter cellsdivision of the cytoplasmbegins during telophaseanimals - cleavage furrow developed, gradually deepens and separates the cytoplasm to form 2 cellsplants - cell plate forms

Attachments

Mitosis.mpg

The Stages of Mitosis.mpg