Mitosis Cell division Agenda Cell cycle Mitosis Overview

Mitosis Cell division

Agenda Cell cycle Mitosis Overview When things go wrong

The Expectations 2. 5. 1 Outline the stages in the cell cycle, including interphase (G 1, S, G 2), mitosis and cytokinesis

The Cell Cycle… • Cells have a life cycle, called the cell cycle • The cell cycle consists of 3 stages: – Interphase (growth and replication) – Mitosis (Nuclear(DNA) division) – Cytokinesis (cytoplasm division)

The Cell Cycle G 1 Synthesis of DNA for Duplication of chromosomes Phase of rapid cell growth S Growth and preparation for cell division G 2 M

Interphase • 1. Stage G 1: primary growth phase. Increase in proteins and in the number of cell organelles. • 2. Stage S: indicates the synthesis of DNA. A. k. a. DNA replication • 3. Stage G 2: Chromosome condensation, preparation for mitosis. • Longest stage of cell cycle (The part where it does not divide). (G 1, S, G 2). Human cells contain 46 chromosomes during the G 1 stage of interphase. This is doubled to 92 strands (still considered 46 chrom) during the S stage of interphase.

Stages of Cell Cycle • Mitosis(M phase) –refers to the process of nuclear division • Cytokinesis (C phase)- occurs after mitosis and is the actual physical division of the cell. Not included in mitosis • Interphase: (G 1, S, G 2)

Why do cells divide? 1. If cells got too large, they would not be able to carry out their functions to survive 2. Growth: allow organisms to grow from a single cell to a multi-celled organism 3. Maintenance: allows new cells to replace worn-out or dead cells 4. Repair: regenerates damaged tissues

Why Divide? It is because the Surface area of a cell to its cytoplasm volume ratio affects the exchange of materials and wastes through the cell.

The Basics: Genetic Material Chromatin in the cell during interphase is structurally loose

DNA • Chromosome: DNA and associated proteins (nucleosomes/histones) that help condense chromosome into a smaller area during mitosis.

Chromosomes one chromosome (unduplicated) Chromosome: a long piece of coiled DNA and proteins. The number of chromosome in each organism differs. 46 in humans. Seen only when the cell divides. Sister chromatids: 2 identical copies of the same chromosome one chromosome (duplicated) Centromere Sister Chromatids

Difference between Plant and Animal Cell Division Uses of Mitosis in Eukaryotic Cells: a. during growth of the individual. b. when tissues have been damaged and need to be repaired (as in healing of a cut). c. to reproduce asexually.

The Expectations 2. 5. 2 State that tumours (cancers) are a result of uncontrolled cell division and that these can occur in any organ or tissue

Cancer • Mitosis and cell division are under strict control. Only producing cells when needed for growth and repair • Tumour repressive genes- inhibit cell division • Prot-oncogenes- stimulate growth/division

Cancer • Cancer: Disorder in which some of the body's cells lose the ability to control their growth. • Tumour - repeated, uncontrolled cell division to form a mass of cells. This can happen in any organ. Some tumours grow large and spread to other parts of the body (metastasis). The diseases caused by the growth of tumours is known as cancer. – Tumours can be benign (harmless) or malignant (spread)

Causes • Carcinogens (increase chances of mutation leading to cancer) – Radiation (gamma, UV, x-ray etc. ) – Chemicals (textile dyes, paints and inks) – Viruses (hepititis B and C and HPV)

Removal • Surgical– physically excise the tumour cells • Radiation– using strong ionising or nuclear radiation beam which can be directed to a point and burn the cells • Chemotherapy– Uses chemicals to destroy all rapidly dividing cells by medication. Can destroy other rapidly dividing cells (hair, stomach/intestinal cells, sperm)

Cancer vs. Normal cells Cancer cells Normal Cells Make exact copies of themselves during mitosis Do not stop reproducing Behave independently Metstacize, no controlled death Reproduce 50 -60 cells Work dependently/stick together Self destruct “apoptosis” when old

The Expectations 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 chloroplasts

Interphase • Most of the time of a cell’s life • Many chemical reactions – Biochemical reactions, DNA transcription and translation and DNA relication – # of mitochondria and chloroplasts increase in G 2

The Expectations 2. 5. 4 Describe the events that occur in the four phases of mitosis -PMAT-

Prophase *chromatin condenses into chromosomes that contains 2 sister chromatids attached by a centromere * Centrioles move to poles *the nuclear envelope and nucleolus disintegrate *Mitotic spindle forms from microtubules *the pair of sister chromatids attach to the spindle at their * Sister chromatids centromeres. present *in animal cells, a pair of centrioles move to each end, called the poles * During late prophase the nuclear envelope breaks down and each chromosome is connected to a spindle fibre by its centromere

Metaphase *Each chromosome becomes completely condensed. The chromosomes line up at the centre of the cell. Line up at the equitorial plate (equator) *The mitotic spindle (made of tubes) is complete and extend from each pole (centrioles) to the middle of the cell.

Anaphase • The sister chromatids separate at the centromere. Each is now called a chromosome. The separated chromosome are pulled to opposite poles by the spindle fibres

Telophase • • • Chromosomes have arrived at the poles Spindle disappears Centrioles replicate (in animals) Nuclear membrane reappears Nucleolus beocmes visible Chromosomes become chromatin

Cytokinesis • The cell divides the cytoplasm and organelles into two portions (splitting known as cytokinesis) • The cell membrane cleaves inward and in plant cells a cell plate forms, nuclear membrane reforms and spindle disappears • 2 identical daughter cells result

Mitosis is an Animal cell Metaphase Anaphase Chromosomes line up. The centromeres divide and the resulting chromosomes, at the equatorial plate. Chromosomes continue move to opposite poles of the The nuclear membrane to condense. Early Prophase completely dissolves. cell. An identical set The centrioles assemble (homologues) of chromosomes and spindle moves to each pole. attach to the The chromosomesfibres condense, becoming shorter centromeres and thicker. of thetochromosomes. The centrioles move opposite nuclear membrane poles of the cell and spindle starts to dissolve. fibres start to form. Telophase DNA replicated and cell Chromosomes lengthen again, prepares for division. In the spindle fibres dissolve, and a Interphase humans, 46 chromosomes nuclear membrane forms around are duplicated (46 pairs). Telophase the chromosomes. In humans, Late Prophase Interphase each new nucleus contains 46 unique chromosomes http: //www. youtube. com/watch? v=Ahg. Rh. Xl

Cell Death • Apoptosis: regulated or controlled cell death of cells that are no longer useful. This is also used to control cells that have stopped performing properly – E. g your body must produces cells to fight a viral infection. When the infection is gone the cells are removed by apoptosis

Mitosis Summary Two divisions occur during cell division • Nuclear division (mitosis) and cytoplasmic division (cytokinesis) During interphase genetic material is replicated 2 Identical daughter cells produced Embryonic growth is a result of repeated mitotic divisions • A zygote is one cell after fertilization. As divisions occur, specialization occurs.

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