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Transcript
Cell Growth and Division Growth vs. Division • When an animal or plant grows, what happens to its cells? • Does an animal get larger because each cell increases in size (grows) or because it produces more of them? Why can’t cells grow forever? • REASON 1: Not enough DNA!...as the cell increases in size, it keeps the same amount of DNA. Eventually the cell will grow too much for the DNA to control all its activities Memory Trick: Think of DNA like a library of books. If a town (cell) is too big, people may have to wait for books! Why Can’t Cells Grow Forever? • REASON #2: Surface area of membrane doesn’t increase as quickly as cell volume Too little membrane not enough exchange of materials (nutrient absorption and waste removal) between cell and environment Cells need a: • (Large surface area) for more materials to pass in and out of the cell… • (Small volume) less distance within the cell for materials to have to travel Specialized Cells • Villi (stomach lining) – absorbs food & nutrients • Alveoli (lungs) – exchanges oxygen and carbon dioxide (oxygen in and carbon dioxide out) • Root hairs (plants) – absorbs water and minerals ALL of these specialized cells have: - increased surface to volume ratios because - their function is to absorb large quantities of material (more surface area allows for more efficient absorption rates) Surface Area & Volume • Surface area of cube 6 sides x area of each side 6 x length x width = surface area • Volume of a cube length x width x height Which of the cubes would have a larger surface area to volume ratio? • Calculate it… 1 cm3 2 cm3 3 cm3 6 cm2 24 cm2 54 cm2 1 cm3 8 cm3 27 cm3 Surface Area Volume Surface area : Volume 6:1 (24 : 8) (54 : 27) 3:1 2:1 The Solution? • Before a cell becomes too large, it divides to form 2 “daughter cells”. • This process is called cell division • Cell division can only happen once a cell has made a copy of its DNA so that each daughter cell can have a full genetic library Cell Division in Prokaryotes • DNA is copied and divided into two cells • Creates two identical daughter cells • Process is called Binary Fission Cell Division in Eukaryotes • DNA is found in the nucleus • Chromatin is DNA & protein threads that coil into chromosomes during cell division. Structure of Chromosomes • Coiled threads of DNA and proteins. • Contains genes (hereditary information) • Must successfully divide for new cells to be made Structure of Chromosome Chromatids: 2 identical copies Of DNA that are connected to Form a chromosome Centromere: the area where chromatids are attached (usually at the middle of the chromatids) Chromosome #’s • The cells of every organism have a specific number of chromosomes Cell Type # of Chromosomes Fruit Flies 8 Carrots 18 Human 46 Diploid vs. Haploid Cells • Diploid Cells (2n) = 2 sets of chromosomes…one from each parent (Example: human body cell has a diploid number of 46) • Haploid Cells (n)= only have 1 set of chromosomes (Example: Sperm or Egg Cell has a haploid number of 23) Types of Chromosomes • Sex chromosomes = determine the sex of an organism; either X or Y • Autosomes = all the other chromosomes in an organism Cell Cycle • • • The series of events that cells go through as the grow and divide During the cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which then begins the cycle again 2 Main Parts 1) Interphase 2) Cell Division Interphase • Time between divisions where cell grows and replicates DNA • 3 Parts 1) G1 = cell grows and matures 2) S = DNA is copied 3) G2 = cell http://www.cellsalive.com/cell_cycle.htm prepares for division Mitosis • This involves division of the nucleus • 4 Phases 1) Prophase 2) Metaphase 3) Anaphase 4) Telophase Part 1: Prophase • Coiling of DNA into chromosomes • Nuclear membrane breaks down • Mitotic Spindle forms using centrosomes / centrioles What is the mitotic spindle? • 2 Structures located in the cytoplasm called centrioles move towards opposite sides of the nucleus • Microtubules (protein tubes) called spindle fibers grow from the centrioles • Spindle fibers attach to chromosomes at the centromere and help pull chromatids apart NERD Part 2: Metaphase • Spindle fibers move chromosomes to the center of the dividing cell Part 3: Anaphase • Chromatids of each chromosome separate at the centromere and move toward opposite poles of the dividing cell Part 4: Telophase • Chromosomes reach poles of cell • Spindle breaks down • Chromosomes uncoil into chromatin • Nuclear envelopes and 2 nucleoli form Cytokinesis • Division of the cytoplasm • Animal Cell: Cleavage Furrow (cell membrane pinches in ) • Plant Cell: Cell Plate (cell wall grows between daughter cells) Mitosis in Real Cells http://www.cellsaliv e.com/mitosis.htm ..\..\..\Downloaded Videos\The Stages of Mitosis.avi ..\..\..\Downloaded Videos\Cell Division and the Cell Cycle.avi Modern Cell Theory – With Cell Division! Original Cell Theory: 1) All living things are made of cells. 2) Cells are the basic unit of structure and function in living things 3) All cells come from pre-existing cells Additions to the Cell Theory: 1) Energy flow (metabolism and biochemistry) occurs in cells 2) Cells contain hereditary information (DNA) that is passed from cell to cell during cell division 3) All cells are basically the same in chemical composition in organisms of similar species. (ex: all cell membranes are made of phospholipids ; all plant cell walls are made of cellulose – a polysaccharide) Rate of Cell Division • The rate of cell division is different for different types of cells Division Rate Do not divide after tissue is mature Cell Type Nerve Cells, Muscle Cells Do not normally divide but Liver Cells can be stimulated to do so (ex: if a portion of the liver is removed surgically) Divide constantly and rapidly Skin Cells, Epithelial Cells, Sperm Cells, Bone Marrow Cells Fun Facts about Cell Division Rate in Various Cell Types • The average red blood cell lives only about 120 days. There are about 2.5 trillion of them in an adult body. To maintain this number, about 2.5 million new red blood cells must be produced each second by the division of stem cells in the red bone marrow. • All told, about 2 trillion cell divisions occur in an adult human every 24 hours; about 25 million a second! Cell Specialization • A single-celled organism is called unicellular. Examples: bacteria, algae (plant), yeasts (fungi) • These organisms perform ALL of their functions in ONLY ONE CELL using different organelles!!! • Multicellular organisms are made up of MANY cells. • These organisms have cell specialization— different types of cells with different structures for different jobs/purposes. • As cells specialize, only DNA related to the functions of a particular cell remains active. Stem Cells • All cells in your body came from a single fertilized cell (sperm + egg). • Most cells become specialized before birth. Once a cell becomes specialized, it cannot be changed into another type of cell. • Stem cells are cells that have not become specialized. • Stem cells can be found in developing embryos or adult bone marrow Cells – What do they really look like? • Cells have drastically different shapes and sizes depending on their functions Levels of Cell Organization • Cells—the smallest unit of life Example: Neuron • Tissues—a group of similar cells working together Example: Nervous Tissue • Organs—a group of similar tissues working together Example: Brain, Spinal Cord, Eye • Organ Systems—a group of organs working together Example: nervous system • Organism—the entire multicellular living thing Example: YOU!