CELL GROWTH & DIVISION Sapling 3.4 Cell Cycle & Mitosis CP Biology Paul VI Catholic High School

CELL GROWTH & DIVISION I.CHROMOSOME “ANATOMY” A. Chemistry: 1. DNA (40%) One continuous Strand of DNA Each (human) approx. 5.0 cm. Contains 140,000,000 nucleotides 2. PROTEIN (60%) a. Histone Protein b. Scaffolding Protein

CELL GROWTH & DIVISION Four types of proteins: a. Histone “octad” (8 proteins) Positively charged Promotes DNA coiling Forms NUCLEOSOME b. Scaffolding Proteins: “Backbone” of DNA coiling

CELL GROWTH & DIVISION

c. Cohesin: Integral part of Centromere Responsible for binding sister chromatids together d. Condensin: Joins loops of coiled DNA Aids in condensing chromosome

CELL GROWTH & DIVISION

CONDENSIN

CELL GROWTH & DIVISION

B. STRUCTURE: 1. Centromere: Indentation on chromosome Variable placement 2. Sister Chromatids: Replicated chromosome Contains identical genes

CELL GROWTH & DIVISION

3. Homologous Chromosomes Contains similar genes for same traits one from each parent Alleles: different gene variations for same trait on “homologues”

CELL GROWTH & DIVISION

B. STRUCTURE: 4. Heterochromatin: Highly condensed portions of chromatin Unable to be “read” 5. Euchromatin: Condensed only in cell division Allows “expression” of DNA 6. Karyotype: Array of chromosomes of an individual (human = 46)

CELL GROWTH & DIVISION

a. Diploid (2n): Represents the two sets of homologous chromosomes in a somatic cell b. Haploid (n): Represents one set of chromosomes (i.e. from one parent) in a somatic cell.

CELL GROWTH & DIVISION

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Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

Mitosis

B. MITOSIS (M Phase): 1. Prophase: Chromosome condensation Spindle apparatus assembled Nuclear envelope breaks down E.R. absorbs; Golgi dissembles Mitosis

B. MITOSIS: 1. Prophase: Microtubule Assembly completed Kinetochore Microtubules Astral Microtubules Polar Microtubules Mitosis

B. MITOSIS: 2. Metaphase: (Division of centromere) Alignment of chromosomes Kinetochore attachment Centromeres Divide “Metaphase Plate” Mitosis

B. MITOSIS: 3. Anaphase: Shortest of the phases Sister chromatids pulled apart Centromeres move to poles 4. Telophase: Spindle disassembled Nuclear envelope re-forms Gene expression commences Mitosis

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C. CYTOKINESIS: Cytoplasmic division 1. Animal Cells: Constriction furrow (actin) Furrow deepens to division 2. Plant Cells: Cell Plate forms Primary cell wall of cellulose Secondary cell wall of lignin Middle lamella of pectin

C. CYTOKINESIS: 3. Fungi/Protists: Mitosis occurs in intact nucleus Nuclear division occurs after mitosis is complete Organelle replication is not equally distributed to daughter cells

Cell Cycle Control

III. CELL CYCLE CONTROL A. Extracellular Controls: 1. Growth Factors 2. Mitogens 3. Survival Factors B. Intracellular Controls: 1. Checkpoints 2. Cyclin Dependent Kinases (Cdk’s) Cell Cycle Control

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Extracellular Controls: 1. Mitogens: Stimulate cell division by relieving negative controls “Release the brakes” (release Cdks) Primarily in G 1 Stage Responds to growth signals Examples: PDGF (Platelet Derived Growth Factor) EGF (Epidermal Growth Factor) Cell Cycle Control

Extracellular Controls: 2. Growth Factors: Bind to receptors on the cell membrane surface and activate intracellular signaling. 3. Survival Factors: Signals from other cells preventing apoptosis. Competition (cells with enough SF continue living) Cell Cycle Control

Intracellular Controls: 1. Checkpoints: Specific sites in the cycle that monitor the progress of cell division. Cell Cycle Control

G0G0

Intracellular Controls: a. G 1 Checkpoint: “Restriction Point” in animal cells, “Start” in yeast cell. Assesses environmental conditions b. G 2 Checkpoint: Triggers start of M Phase c. M Checkpoint: Assesses mitosis Cell Cycle Control

47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G 1 (growth) G0G0 G 2 checkpoint Mitosis checkpoint. Mitosis will occur if DNA has replicated properly. Apoptosis will occur if the DNA is damaged and cannot be repaired. S (growth and DNA replication) M Cytokinesis T elophase Anaphase Metaphase Late prophase Prophase Interphase G1 checkpoint Cell cycle main checkpoint. If DNA is damaged, apoptosis will occur. Otherwise, the cell is committed to divide when growth signals are present and nutrients are available. M checkpoint Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned. M G2G2 G1G1 G 2 (growth and final preparations for division)

Intracellular Controls: Cyclins: Proteins that undergo synthesis & degradation in each cell cycle Cyclin Dependent Kinases (Cdk’s) Proteins that activate or suppress Inactive until bound to a CYCLIN Express their activity at the various “checkpoints” by adding PO 4 group Cell Cycle Control

Checkpoint video Cell Cycle Control

Cyclins degraded. Each step only happens once per cycle.

G 1 Checkpoint:  Called “Restriction Point” in animal cells  Multiple control factors required Cyclin & G 1 Cdk “Rb Protein” (Retinoblastoma) “P 53 Protein” Proto-oncogenes vs. Oncogene Cell Cycle Control

52 Regulation at the G1 Checkpoint Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. P P RB protein RB protein E2F CDK not present E2F not released released E2F E2F binds to DNA. DNA cell cycle proteins phosphorylated RB CDK present b. P P P P breakdown of p53 no DNA damage DNA damage phosphorylated p53 DNA repair proteins apoptosis p53 binds to DNA. DNA p53

Rb Protein: Blocks S Phase Influenced external factors P 53 Gene: “Guardian Angel gene” Assesses DNA Prevents S Phase if DNA inaccurate Allows time for repair & correction Severe DNA damage  apoptosis “Better dead than read” Cell Cycle Control