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