CELL DIVISION TOPIC 2.5

ASSESSMENT STATEMENTS 2.5.1 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

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

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

Prophase Chromatin fibers become more tightly coiled to form chromosomes Nuclear envelope disintegrates and nucleoli dissappear Mitotic spindle forms Centromere of each chromosome has a central region called the kinetochore that attaches to the spindle Centrosomes move toward opposite poles of the cell due to lengthening microtubules

Metaphase Chromosomes move to middle or equator of cell (metaphase plate) Chromosome’s centromeres lie on the plate Movement of chromosome is due to the action of the spindle which is made of microtubules Centrosomes now at opposite poles

Anaphase Two sister chromatids of each chromosome are split Chromatids move towards opposite poles of the cell Chromatid movement due to shortening of microtubules Since the centromeres are attached to the microtubules, they move toward the poles first Each pole has a complete, identical set of chromosomes

Telophase Chromosomes are at each pole Nuclear membrane (envelope) begins to reform around each set of chromosomes Chromosomes begin to elongate to form chromatin Nucleoli reappear Spindle disappears Cell is elongated and ready for cytokinesis

Cytokinesis In animals In plants 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