Cell Growth and Division

Why are cells so small? DNA Diffusion Messages from the nucleus must be able to reach all parts of the cell Diffusion Nutrients must enter and wastes must leave If the cell was too big, diffusion would happen too slowly

Why are cells so small? Surface Area vs. Volume As a cell grows larger, the volume increases faster than the SA A bigger cell needs more nutrients, but has relatively less SA to take in those nutrients

Surface Area vs. Volume Cell Size 5 cm 10 cm Surface Area (l×w×6) Volume (l×w×h) 125 cm3 1000 cm3 SA to Volume Ratio 150/125 = 6:5 600/1000 = 6:10

Cell Cycle Cells divide before growing too large Before dividing, cells must prepare Preparation = Interphase G1 phase: Cell grows larger S phase: Cell makes new DNA for daughter cell G2 phase: Cell makes new organelles for daughter cell

Cell Cycle

Chromosomes Each chromosome is replicated during the S phase Centromere Sister Chromatids Each chromosome is replicated during the S phase A replicated chromosome has two identical sister chromatids connected by a centromere

Mitosis CLICK FOR MITOSIS VIDEO

Mitosis Four Stages: Prophase (pro- means first) Metaphase (meta- means middle/after) Anaphase (ana- means apart) Telophase (telo- means far away/end)

Prophase Chromatin condenses into chromosomes condensing Chromatin condenses into chromosomes Nuclear envelope and nucleolus disintegrate Centrioles migrate to opposite ends of the cell Spindle fibers form in foot ball shape across cell

Metaphase Chromosomes line up in the middle (equator) of the cell Spindle fibers attach to centromeres

Metaphase

Anaphase Sister chromatids separate Spindle fibers shorten, pulling chromatids to opposite ends of cell Animal cells begin to pinch in Plant cells begin to form cell plate in the middle

Anaphase

Telophase Nuclear membrane built from ER around each set of chromosomes Nucleolus reforms in each nucleus Chromosomes become mass of chromatin

Two cells dividing into four Telophase Two cells dividing into four

Cytokinesis Final division of cytoplasm resulting in two daughter cells Animals – CM pinches together Plants – Cell plate forms new CM dividing the daughter cells

Plant Cell Division CLICK HERE FOR PLANT MITOSIS VIDEO

Which phases can you see? Anaphase Prophase Metaphase Telophase Interphase

Knowing when to divide Cyclins Protein that regulates the cell cycle in eukaryotes Internal regulators – tell the cell when to enter mitosis External regulators – control the rate of the cell cycle

Cellular Response to Injury

Effect of Cyclins Cytoplasm is injected into a second cell in G2 phase Cytoplasm is removed from cell in mitosis Second cell enters mitosis

Cancer Cancer results when cells do not respond to cell cycle regulators Cells grow unregulated, forming a tumor Tumor damages surrounding tissue

Leukemia – Blood cancer

Mammary (Breast) Cancer

Skin Cancer