•
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 Chromosome
Duplicated 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 Chromosome
Duplicated Chromosome
Centromere
Chromatid
Chromatid
Chromatid
Sister Chromatids
•
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
Fig. 9.3, p. 151
Slide 3
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