BIOLOGY UNIT
6
THE CELL CYCLE AND
MITOSIS
A. Cell Division
1. the reproduction of cells
2. the continuity of life depends on cell division a. every cell comes from a cell
3. can produce progeny for some organisms
4. can function in renewal and repair, replacing dead or
THE CELL CYCLE AND
MITOSIS
B. From DNA to chromosomes
1. DNA molecules are “packaged” into chromosomes a. DNA binds with proteins to make chromatin
b. chromatin keeps coiling upon itself to form chromosomes
THE CELL CYCLE AND
MITOSIS
2. chromosome number:
a. karyotype
1. a set of chromosomes
2. ex. human’s somatic cells contain 46 chromosomes
THE CELL CYCLE AND
MITOSIS
3. ex. human’s reproductive cells have 23 chromosomes
a. called haploid
1. ½ the number of chromosomes b. female chromosomes are XX
THE CELL CYCLE AND
MITOSIS
3. chromosome structure:
a. a duplicated chromosome has 2 sister chromatids
THE CELL CYCLE AND
MITOSIS
C. The Cell Cycle
1. the life of a cell from the time it is first formed from a dividing parent cell until its own division into two cells
2. defined as: sequence of events that occurs in cells from one cell
THE CELL CYCLE AND
MITOSIS
3. Five Parts to the Cycle:
a. G1 Period (Gap 1) 1. cell growth
2. cell doubles in size
3. enzymes, organelles double b. S Period
1. DNA replication takes place
2. when coiled, both strands of DNA form each side of the chromosomes, called the sister chromatids
c. G2 Period (Gap 2)
1. growth and preparation for cell division
THE CELL CYCLE AND
MITOSIS
d. Mitosis
1. the division of the cell nucleus e. Cytokinesis
1. the division of cytoplasm
THE CELL CYCLE AND
MITOSIS
4. a typical human cell would undergo 1 division in 24 hours
a. Mitosis – less than 1 hour b. S phase – 10- 12 hours c. G2 phase – 4-6 hours d. G1 phase – 5-6 hours
THE CELL CYCLE AND
MITOSIS
D. Mitosis
1. division of the cell nucleus in which chromosomes in parent cells
divide into 2 identical sets
2. the offspring will have the same DNA 3. why do we need mitosis?
THE CELL CYCLE AND
MITOSIS
4. Steps:
a. Prophase
1. as the chromatin becomes more tightly coiled,
visible chromosomes appear
2. nucleus and nuclear membrane disappear
3. each duplicated chromosome appears as two
identical sister chromatids
joined together
4. centrosomes move to opposite ends of the cell
a. an organelle functioning only in cell division,
made of centrioles
THE CELL CYCLE AND
MITOSIS
1. microtubules that extend out from the centrosomes 2. structures that will eventually separate the
chromosomes
a. some microtubules, called kinetochore microtubules actually attach to the chromosomes at the kinetochore, a
THE CELL CYCLE AND
MITOSIS
b. Metaphase
1. chromosomes line up along the center, equator, of the cell 2. the longest stage of Mitosis, lasting about 20 minutes
THE CELL CYCLE AND
MITOSIS
c. Anaphase
1. chromosomes divide at the centromere
2. sister chromatids move to opposite sides of the cell - become just chromosomes
a. pulled at the centromere region b/c they are attached to the kinetochore
THE CELL CYCLE AND
MITOSIS
d. Telophase (basically the opposite of Prophase)
1. chromosomes are now at opposite sides of the cell 2. centrioles and spindles disappear
3. nucleus and nuclear membrane reappear
THE CELL CYCLE AND
MITOSIS
5. Cytokinesis
a. immediately following mitosis b. last step in the cell cycle
c. cytoplasm from original cell splits and forms 2 new cells
THE CELL CYCLE AND
MITOSIS
e. cleavage furrow – where the cell pinches into two (starts to form in Telophase)
1. plant cells do not produce a cleavage furrow b/c they have a cell wall
THE CELL CYCLE
AND MITOSIS
E. Binary Fission
THE CELL CYCLE AND
MITOSIS
F. Loss of Cell Cycle Controls in Cancer Cells
1. caused by abnormal cell division or growth
2. tumor – mass of abnormal cells that have divided
uncontrollably, invade tissues
a. transformation – when a single cell becomes a
cancer cell from a normal cell
b. if “unseen” by the human defense system, it can
divide and form a tumor
THE CELL CYCLE AND
MITOSIS
d. malignant tumor – impairs the functions of one or more organs, have cancer
1. cancer cells have been found to have an abnormal number of chromosomes
e. metastasis – the spread of cancer cells to locations outside of their original site
THE CELL CYCLE AND
MITOSIS
a. carcinogens – cancer causing agents
1. radiation, viruses, chemicals, nicotine 2. damage the DNA
