Chapter 9: Chromosomes and Mitosis p
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 genes Each chromosome may contain hundreds - thousands of genes Humans have 35, ,000 genes that code for proteins
Chromosomes located in cell nucleus made 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 form During 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 _____ chromosomes Most plants and animals have between ____ and ____ chromosomes
The Cell Cycle Cell cycle - sequence of cell growth and division Do 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 circle generation 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 Interphase m ost of the cell's life no cell division G1 - no DNA synthesis occurs, growth period, longest stage S - 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 mitosis The chromosomes become visible Centrioles - separate and take up positions on opposite sides of the nucleus Spindle begins to form - its job is to help separate the chromosomes Nuclear envelope breaks down Prophase
Only lasts a few minutes Chromosomes line up across the center of the cell Centromere of each chromosome is attached to the spindle Metaphase Centromeres split Sister chromatids separate and become individual chromosomes Chromosomes move to opposite ends of the cell Anaphase
Final stage of mitosis Chromosomes begin to disperse into a tangle of dense material Nuclear envelope reforms around each cluster of chromosomes Spindle breaks apart Nucleolus becomes visible in each daughter nucleus Telophase
Cell Cycle Cytokinesis formation of 2 separate daughter cells division of the cytoplasm begins during telophase animals - cleavage furrow developed, gradually deepens and separates the cytoplasm to form 2 cells plants - cell plate forms
Attachments Mitosis.mpg The Stages of Mitosis.mpg