The Cell Cycle (IPMAT)

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Transcript The Cell Cycle (IPMAT)

The Cell Cycle and Mitosis
Lesson 5
January 25th, 2011
The Cell Cycle (IPMAT)
• Cells alternate between stages of dividing and not
dividing. This is called the cell cycle.
• In the cell cycle the initial cell is called the parent
cell and the two identical cells are called
daughter cells. The daughter cells have
Identical DNA
Functions of Cell Division
Healing and tissue repair
• Dead cells are replaced by new
Functions of Cell Division
• Cell division increases the number of cells.
• Cells have an optimal size. Surface area to
cytoplasm ratio
Functions of Cell Division
Reproduction of organisms
• Perpetuates life
• Fundamental to unicellular and multicellular
• Every cell contains chromosomes.
• Each chromosome is a long piece of coiled
DNA and proteins. The number of
chromosomes in each cell differs between
– Humans 46 – 23 matching pairs
– Hermit crabs 254
• For mitosis to occur, each chromosome must
be copied. The identical copies are called sister
Mitosis Movie
The Cell Cycle
There are four phases in the cell cycle:
• First growth phase (G1)
• Synthesis phase (S)
• Second growth phase (G2)
• Mitosis (M)
The Three Phases of Interphase
• -A cell spends 90 percent of its time in interphase.
1. First Growth Phase (G1)
• Period of growth
• Produces new proteins and organelles
2. Synthesis Phase (S)
• Makes (synthesizes) an entire copy of the DNA of
the cell.
• Key proteins associated with chromosomes also
The Three Phases of Interphase
3. Second Growth Phase (G2)
• Produces organelles and structures needed for
cell division
Mitosis (PMAT)
• When the cell is ready to divide it enters mitosis.
• All preparation up until this phase must be complete
as it requires a lot of energy.
• Contains 4 stages
1. Prophase(IPMAT)
Early Prophase
• The chromatin condenses to form
• The centrioles move toward the poles.
• - Spindle fibres form.
1. Prophase(IPMAT)
Late Prophase
• The nuclear envelope breaks down.
• Each chromosome is connected to a spindle fibre
at its centromere.
• Centrioles move to opposite ends of cell forming
poles of the mitotic spindles
2. Metaphase (IPMAT)
• -Each chromosome becomes completely
• -The chromosomes move toward the centre of
the cell and line up at the middle of the cell.
• - The mitotic spindle is completely attached
from the mitotic spindle to the centromere
3. Anaphase (IPMAT)
• Sister chromatids separate at the centromere.
• Each chromatid is now a complete chromosome.
• The separated chromosomes are pulled to
opposite poles of the cell.
4. Telophase and Cytokinesis
• Mitotic Spindle breaks down
• Two new nuclei form
• The cytoplasm and cell membrane pinch in half to
form two new daughter cells.
4. Telophase and Cytokinesis
• The process of splitting the cytoplasm is known
as cytokinesis.
• In plant cells, the cell plate forms the cell wall and
inner plasma membrane in each of the new cells.
• Each of the new cells enters the G1 phase of
the cell cycle, and the cell cycle is repeated.
• 1. What is the purpose of the cell cycle?
• The purpose of the cell cycle is cell division.
Cell division allows for:
– Healing and tissue repair
– Growth
– Reproduction
• 2. Define the term “interphase” and describe its
• Interphase is the time period when the cell grows,
duplicates its DNA and prepares for mitosis.
• 90% of the cell cycle is spent in interphase.
• Without this stage, it would not be possible for the
cell cycle to occur.
• 3. (a) What is mitosis?
• (b) Why is mitosis important to the cell?
• (a) Mitosis is the process of cell division.
Genetic information in the nucleus is packaged
into two equal portions.
• (b) Mitosis is important for growth and repair.
• 4. Define and distinguish between the following
terms: chromosome, centromere, and sister
• Chromosomes: a long piece of coiled DNA and
• Centromere: place at which the two sister
chromatids are joined together
• Sister chromatids: the identical copies of a
chromosome that are attached together
• 5. Explain the meaning and importance of the
term “cytokinesis.”
• Cytokinesis is the process by which the
cytoplasm splits into two portions. This produces
two new cells that enter interphase.
Micro viewer 55
• Do the questions and hand them in