Chromosomes Chromatin – long strands of DNA wrapped around proteins Chromosome – a rod-shaped structure that forms when a single DNA molecule coils tightly before cell division

Single ChromosomeDuplicated Chromosome

Chromatid – one of two copies of each chromosome Sister Chromatid – two identical copies of the chromosome Centromere – a protein disk that attaches the two chromatids

Single ChromosomeDuplicated Chromosome ChromatidSister Chromatids Centromere Chromatid

Human cells have 23 different chromosomes Contain 2 copies of each chromsome for a total of 46 Homologous chromosomes – two copies of each chromsome that are similar in shape, size and have similar genetic information

Cell Division Cell division – process by which new cells are made from an existing cell Two types of cell division Mitosis – makes somatic cells (body cells) Meiosis – makes gametes (sperm and egg)

The Cell Cycle Cell Cycle – sequence of growth and division of a cell 5 Phase of the Cell Cycle 1.G1 Growth of cell Makes new proteins and organelles

2. S DNA replicates 3. G2 Produces proteins needed for mitosis or meiosis 4. M Mitosis or Meiosis 5.Cytokinesis – cytoplasm divides separating into 2 daughter cells G1, S, and G2 combined are called Interphase Where the cell spends most of its life

Video

Mitosis Mitosis – process by which the nucleus of a cell is divided into 2 identical nuclei with the same number of chromosomes Mitosis is divided into 4 stages

1. Prophase Chromatin coils into chromosomes Nuclear envelope breaks down Centrioles form and move to opposite poles As centrioles separate, spindle fibers form which are microtubules (protein cables) Longest phase of mitosis

2. Metaphase Spindle fibers attach to the chromosomes at the centromere Chromosomes line up in the middle

3. Anaphase Centromeres split and sister chromatids are pulled apart toward opposite poles Each chromatid may now be called a chromosome

4. Telophase Chromosomes reach opposite poles Spindle fibers break Chromsomes uncoil Nuclear envelope forms

Cytokinesis Two daughter cells are formed

Cytokinesis differs between plants and animals Animals – the cell membrane pinches in along the center of the cell

Plants – have a cell wall so cell membrane can’t pinch in Instead a cell plate is laid down across the center

The Cell Cycle

Regulating the Cell Cycle Normal Cell Growth Scientists have worked long and hard to discover the factors that initiate and control cell division. A clear understanding of these control factors can benefit medical research. Scientists have found that a specific protein called cyclin regulates the cell cycle.

Uncontrolled Cell Growth Occasionally cells lose control of the cell cycle This loss of control may be caused by… Environmental factors Changes in enzyme production Cancer is a result of uncontrolled cell division Cancer cells divide uncontrollably and form masses of cells called tumors. Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.

Cancer