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CELL DIVISION
TOPIC 2.5
ASSESSMENT STATEMENTS2.5.1 Outline the stages in the cell
cycle, including interphase (G1, S, G2), mitosis and cytokinesis
2.5.2 State that tumors (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue
2.5.3 State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts
2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase, and telophase)
2.5.5 Explain how mitosis produces two genetically identical nuclei
2.5.6 State that growth, embryonic, development, tissue repair and asexual reproduction involve mitosis
The cell cycle• Describes the behavior of cells as
they grow and divide• Produced cells are called daughter
cells• Sometimes cells divide so rapidly
without restraint that they form a solid mass of cells called a tumor (cancer)
• Cancer can occur in any organ or tissue
Interphase• Largest part of the cell cycle• Phases
– G1 – growth of the cell– S – replication of the DNA (synthesis)– G2 – growth of the cell, preparation
for mitosis, increase in organelle number, DNA condenses from chromatin to chromosomes
Chromatin to chromosome• Chromatin condenses through a
process called supercoiling – DNA wraps around histones to produce
nucleosomes– Nucleosomes wrap into a solenoid– Solenoids group together in looped domains– Final coiling produces chromosome
• Before replication in the S phase chromosomes are composed of one molecule of DNA
• After replication the chromosome contains two molecules of DNA
• These 2 molecules called sister chromatids are held together by centromere
Mitosis• When all preparations are made
and the DNA has replicated, the cell moves into mitosis or the M phase
• Four phases:– Prophase– Metaphase– Anaphase– Telophase
Prophase1. Chromatin fibers become more
tightly coiled to form chromosomes2. Nuclear envelope disintegrates and
nucleoli dissappear3. Mitotic spindle forms4. Centromere of each chromosome
has a central region called the kinetochore that attaches to the spindle
5. Centrosomes move toward opposite poles of the cell due to lengthening microtubules
Metaphase1. Chromosomes move to middle or
equator of cell (metaphase plate)2. Chromosome’s centromeres lie
on the plate3. Movement of chromosome is due
to the action of the spindle which is made of microtubules
4. Centrosomes now at opposite poles
Anaphase1. Two sister chromatids of each
chromosome are split2. Chromatids move towards
opposite poles of the cell3. Chromatid movement due to
shortening of microtubules4. Since the centromeres are
attached to the microtubules, they move toward the poles first
5. Each pole has a complete, identical set of chromosomes
Telophase1. Chromosomes are at each pole2. Nuclear membrane (envelope)
begins to reform around each set of chromosomes
3. Chromosomes begin to elongate to form chromatin
4. Nucleoli reappear5. Spindle disappears6. Cell is elongated and ready for
cytokinesis
Cytokinesis• In animals
– Inward pinching of the fluid plasma membrane to form cleavage furrows
• In plants– Forms a cell plate which moves
outward toward the sides of the cell from a central region
• Both results in two separate daughter cells that have genetically identical nuclei
Activities which require involve mitosis• Growth• Embryonic development• Tissue repair• Asexual reproduction
Topic 2.5 Exercise• Create a foldable which outlines
the stages of the cell cycle, including interphase, mitosis, and cytokinesis
• Must include name, description, and illustration for each phase of each stage
• Due Monday November 24th