Transcript Life: The Science of Biology, 8e

THE CELL CYCLE, AND CELL DIVISION
1.
2.
3.
Objectives:
Describe the life cycle of a cell (explain what happens in each phase
of the life cycle)
Describe the process of mitosis and state its function
Explain the role that mitosis plays in transmitting genes from one cell
to the next.
Why Do Cells Divide?
• Unicellular organisms use cell division
primarily for reproduction.
• In multicellular organisms, cell division is
also important in growth and repair of
tissues.
Figure 9.1 Important Consequences of Cell Division
The cell cycle:
Events that occur to produce two eukaryotic cells from
one. (eukaryotic cells have nuclei)
Interphase
A period between divisions, when the cell grows rapidly
and prepares for mitosis by copying its DNA
Most of the life of a cell is spent in interphase
Mitosis
Cell division
The Eukaryotic Cell Cycle
Four events must occur for cell division:
• Reproductive Signal: to initiate cell division
• Replication: of DNA
• Segregation: distribution of the DNA into the
two new cells
• Cytokinesis: separation of the two new cells
Prokaryotic Cell Division
Figure 9.2 Prokaryotic Cell Division (Part 2)
Eukaryotic Cells Division:
• Eukaryotes usually have many chromosomes.
• Mitosis is the process that segregates the
chromosomes.
• The nucleus must be divided into two nuclei
before the cell can split into daughter cells
9.3 What Happens during Mitosis?
Mitosis can be divided into phases:
• Prophase
• Metaphase
• Anaphase
• Telophase
The cell enters mitosis from interphase
Interphase
- each chromosome copies itself to make sister chromatids
(bundles of DNA) that are held together by centromeres
(proteins)
- two identical chromatids joined together are called a
chromosome
Chromatin fibers consist
of DNA and proteins
The centromere is
visible as a
constriction.
Recall DNA replication
1. Prophase
MITOSIS
• Nuclear membrane disappears
• Chromatids (DNA coils) become visible
• Centrioles move to opposite sides of cell and spindle
fibers grow from the centrioles to the centromeres on
each sister chromatid
Prophase
Spindle fibers
Figure 9.10 Mitosis (Part 1)
2. Metaphase
• Chromatids line up in the
centre of the cell
3. Anaphase
• Sister chromatids are pulled
apart by the spindle fibers at
the centromeres
4. Telophase
• Spindle breaks down
• Chromosomes uncoil
• Nuclear envelope and nucleoli
are reformed
• Two daughter nuclei are
formed with identical genetic
information
Figure 9.10 Mitosis (Part 2)
Cytokinesis (follows mitosis)
- division of the cytoplasm
- cell membrane moves in to pinch off
two daughter cells, each with its
own nucleus with identical
chromosomes
Figure 9.12 Cytokinesis Differs in Animal and Plant Cells
Plenary
1. A cell with 10 chromosomes undergoes mitosis.
How many chromosomes would be in each of the
resulting daughter cells?
2. What happens in interphase to allow the cell to
be capable of undergoing future divisions?
3. What is the significance of cytokinesis? What
do you think would happen if this process didn’t
happen?
Interphase - Onion
Prophase - Onion
Metaphase - Onion
Anaphase - Onion
Telophase - Onion
Prophase - Whitefish
Metaphase - Whitefish
Anaphase - Whitefish
Telophase – Whitefish
Count ‘em Up!!!!
Count the cells on the following two slides.
Count the number of cells in interphase and in cell
division (mitosis)
For 20 Onion root tip cells
cells
For 20 Whitefish blastula
# in Interphase
# in Interphase
# in Division
# in Division
What type of cells are these???