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THE CELL CYCLE Chapter 10 Biology CPA The Cells Life of Cycle CELL GROWTH •A cell is limited by its cell size •The larger the cell the harder it is to move through tissue and get nutrients •In order to stay alive and not grow continuously, the cell will divide REASONS WHY TO DIVIDE •DNA •Genetic information stored •Found in the nucleus of the cell •DNA would not be able to keep up with demand of the cell •Transport •Rate decreases as the cell size increases •Takes too long for nutrients and wastes to move in and out of cell SURFACE AREA TO VOLUME •Surface Area • Area on outside of cell where reactions can occur • As a cell increases, the surface area decreases CELL DIVISION AND REPRODUCTION •Asexual Reproduction •Produces identical offspring from a single parent •Used by many single-celled organisms Ex: bacteria •Occurs very quickly •Sexual Reproduction •Produces genetically different offspring from two parents •Fusion of two parent cells CHROMOSOMES •Made up of our DNA •Holds genetic information •Tight coils or rod like structures •Organisms have a specific amount of chromosomes Humans have 46 chromosomes of DNA in every somatic cell CHROMOSOME STRUCTURE •Histones are proteins that DNA wraps around to make the chromosome shape •Chromosomes are made of two sister chromatids • Identical to each other CHROMOSOMES •Centromeres are in the center of a chromosome •Chromosomes are tightly coiled strings of DNA called chromatin •Chromatin is the string-like form of DNA CHROMOSOME NUMBERS •There is a specific number of chromosomes in each organism •Humans autosomes and sex chromosomes •We have 2 sex chromosomes •Either X or Y •We also have 22 autosomes •Which do not code for gender KARYOTYPE •A karyotype is a picture of one set of chromosomes • Shows you sex of organism • Shows your any chromosomal disorders CHROMOSOME NUMBERS •A diploid cell contains 2 sets of each chromosome •Prefix di = 2 •A haploid cell contains only 1 set of each chromosome •Half of the total number •Usually sex cells CELL DIVISION IN PROKARYOTES •Prokaryotes •No nucleus •No organelles •Ex: Bacteria •Reproduction is VERY fast •Copy DNA •Split into two cells •Cell division is called binary fission EUKARYOTIC CELL REPRODUCTION •Eukaryotes •Have a nucleus •Have organelles •Ex: Humans, plants •Complex reproduction •Everything needs to be controlled! •Much longer process – about 18 hours! CELL REPRODUCTION •A cell splits to make 2 identical copies •If asexual reproduction •Only 1 cell involved •This occurs in 3 main stages 1. Interphase – Growth 2. Mitosis – Splitting of the cell 3. Cytokinesis – Splitting of the cytoplasm INTERPHASE •Cell growth •90% of cell’s life is spent in interphase. •3 Part of Interphase: •G1, S, G2 G1 PHASE •The cell is growing •The organelles are doubling S PHASE •Takes place when cells are too big •S = Synthesis of DNA •DNA is replicated so there is a set for each new cell DNA REPLICATES IN INTERPHASE SO THE DAUGHTER CELLS EXACT COPIES OF THE DNA G2 PHASE •Cell growth again •Replication of organelles •Last stage of interphase •Cell prepares for cell division HOW IS DNA COPIED? •Each cell has an protein called helicase •Enzyme the unwinds the DNA making 2 identical strands •http://www.youtube.com/watch?v=zdDkiRw1PdU MITOSIS Cell Division MITOSIS • The part of a cell’s life cycle when the cell’s nucleus divides into 2 identical nuclei •4 steps: •Prophase •Metaphase •Anaphase •Telophase PROPHASE • All organelles disappear • Centrioles separate and move to opposite pole • Chromatin becomes chromosomes • Centrioles shoot off spindle fibers METAPHASE • Chromosomes line up at the equator ANAPHASE •Centromere splits •Sister chromatids attach to the short spindle fibers •Spindle fibers shorten and bring the sister chromatids to opposite poles TELOPHASE •Chromatids become chromatin (one at each pole) • Spindle disappears •Organelles reappear CYTOKINESIS •Once mitosis has finished! •Last stage of cell cycle •Process is when the cytoplasm splits apart •There are now 2 identical cells CYTOKINESIS IN PLANT CELLS •A cell plate forms between the two nuclei. •The cytoplasm divides. •A cell wall forms two daughter cells. CYTOKINESIS IN ANIMAL CELLS •Cell membrane pinches in at equator •Cleavage furrow MITOSIS: DIVISION OF THE NUCLEUS CELLS IN VARIOUS STAGES OF THE CELL CYCLE CONTROL OF CELL DIVISION •Checkpoints (Regulatory Proteins) • DNA repair enzymes will fix any mutations, if checkpoint is passed mitosis will occur •Mitosis checkpoint – if all is correct, the 2 daughter cells will enter G1 phase and start over again •If a cell does not meet requirements for checkpoints, the cell will be programmed to die Apoptosis is controlled cell death Uncontrolled Mitosis is cancer. WHEN CONTROL IS LOST •Enzyme proteins are not functioning properly causing cell to reproduce out of control •Could cause cancer •Cancer cells do not respond to body’s signals that control mechanisms COMPARE/CONTRAST HOW ELSE CAN OUR BODY CONTROL CANCER?
