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The Cell
Topic 2.5
Cell Division
Mitosis
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Cellular division in eukaryotic cells.
Chromatin is arranged into chromosomes.
Chromosomes double.
Cell grows in size.
Cells divide.
Is cellular cloning.
Phases of the Cell Cycle
the ‘life cycle’ of a cell.
There are 2 phases:
1. Interphase
2. M phase (mitotic phase)
a. Prophase
b. Metaphase
c. Anaphase
d. Telophase & cytokinesis
Figure 12.4 The cell cycle
1. Interphase
• The non-dividing phase in a cell
• Lasts about ~ 90% of the cell cycle.
• The cell grows and replicates DNA
preparing for Mitosis.
• There are three periods:
3 periods of Interphase
1.
2.
3.
4.
Go – a cell functioning as normal
G1 phase – first growth phase
S phase- synthesis of DNA
G2 phase- 2nd growth phase
Mitosis is a reliable process. Only one error occurs
Per 100,000 cell divisions.
2. Mitosis: Prophase
• The nucleolus
disappears.
• Chromatin
condenses into
visible
chromosomes.
• There are two
sister chromatids
held together by a
centromere.
• The mitotic spindle
forms in the
cytoplasm.
Figure 12.3 Chromosome duplication and distribution during mitosis
“Pro”metaphase
• The nuclear
envelope
disappears.
• Spindle fibers
extend from each
pole to the cell’s
equator.
• Spindle fibers
attach to the
centromeres.
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase
Metaphase
• Chromosomes
are lined up in
the equator
(middle) of the
cell.
• This is called
the metaphase
plate.
Figure 12.6 The mitotic spindle at metaphase
Anaphase
• Characterized by
movement. It begins
when pairs of sister
chromatids pull apart.
• Sister chromatids move
to opposite poles of the
cell.
• Chromosomes look like a
“V” as they are pulled.
• At the end of anaphase,
the two poles have
identical number and
types of chromosomes.
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.
Telophase and Cytokinesis
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Microtubules elongate the cell.
Daughter nuclei begin to form at the two poles.
Nuclear envelopes re-form.
Nucleolus reappears.
Chromatin uncoils.
Cells split their cytoplasm.
It is basically the opposite of prophase.
Figure 12.5x Mitosis
Figure 12.8 Cytokinesis in animal and plant cells
Figure 12-09x Mitosis in an onion root
Role of Mitosis
•Growth: Multicellular organisms increase their size through
growth. This growth involves increasing the number of cells
through mitosis. These cells will differentiate and specialize
their function.
•Tissue Repair: As tissues are damaged they can recover
through replacing damaged or dead cells. This is easily
observed in a skin wound. More complex organ
regeneration can occur in some species of amphibian.
•Asexual Reproduction: This the production of offspring
from a single parent using mitosis. The offspring are
therefore genetically identical to each other and to their
“parent”- in other words they are clones. Asexual
reproduction is very common in nature, and in addition we
humans have developed some new, artificial methods
Tumors
The cancer cells are a mass of cells produced from uncontrolled cell division
and can occur in an tissue. These cells disrupt biological order and function. If
left unchecked, to bring the whole complex, life sustaining edifice that is the
human body crashing down' This mass is called a tumor.
There are two major types of tumor:
1. Benign Tumors this is a
mass of cancerous cells that do not
invade other areas of the body. These
are not as dangerous to health but
may still require removing to prevent
effects on neighboring tissue
2. Malignant Tumors is a
mass of cancer cells that
may invade surrounding
tissues or spread to distant
areas of the body. Cancer
cells replace normal
functioning cells in distant
sites:
e.g. replacing blood forming
cells in the bone marrow,
replacing bones leading to
increased calcium levels in
the blood, or in the heart
muscles so that the heart
fails.
1. Image is a normal CT. Images 2, 3 & 4
Are PET scans, Light green/blue areas
show cancer cells