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 genes
Each chromosome may contain hundreds - thousands of genes
Humans have 35,000 - 40,000 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
most 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
Cell Cycle
Mitosis
4 phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
The Stages of Mitosis.mpg
Prophase
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
Metaphase
Only lasts a few minutes
Chromosomes line up across the center of the cell
Centromere of each chromosome is attached to the spindle
Anaphase
Centromeres split
Sister chromatids separate and become individual chromosomes
Chromosomes move to opposite ends of the cell
Telophase
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
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