Cells

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					     Unit 4
Cellular Biology
   Textbook Chapter 7
   Review Book Topic 1
                 What is a Cell?
   All living things are made of cells
       Basic structural and functional unit of living things


   Can be composed of a single cell
    (unicellular) or multiple cells (multicellular)

   Cells carry on all life processes of an
    organism
Organization of Living Things
   In multicellular organisms
       Groups of specialized cells form tissues

       Different kinds of tissues are combined to
        form organs which carry out life processes

       Each organ is part of an organ system
        which transports materials throughout the
        body
     History of Cellular Biology
   Robert Hooke (mid-1600s)
       Examined thin pieces of cork

       Observed boxlike structures of the dead walls of
        a plant cell

            Called these boxes: “cells”

       Never studied living cells
   Anton van Leewenhoek (mid-1600s)
       Observed pond water

            Saw microorganisms within the water samples


       Observed and described human blood cells

       Described bacteria
   Robert Brown (early 1800s)
       Observed small, dense, round bodies which
        appeared in all plant cells

            Called the structure the
             “nucleus”
                    Cell Theory
   All organisms are made up of one or more
    cells

   All cells carry on life activities

       The combined activity of individual cells make up
        the life activities of a multicellular organisms

   New cells arise from pre-existing cells
Cell Types



Prokaryotic vs. Eukaryotic
       Prokaryotic Organisms
   Lack internal membrane-bound organelles

   Prokaryotic = “Without nucleus”

   1-10 µm (micrometers) – very small

   Ex. Archaebacteria and Eubacteria
            Cell Characteristics
   Lack a membrane bound nucleus, but instead
    have a single, circular chromosome found in a
    region called a nucleiod

   Contains:
       Cell wall
       Plasma membrane
       Capsule – secretion of a slime-like material to give
        added protection to the cell
    Characteristics Continued
   Most life processes occur on the surface of the
    plasma membrane

   Ribosomes located throughout cytoplasm (protein
    synthesis)

   May use cilia or flagella for movement

   Pili are sexual appendages used in conjugation
    (reproduction)
                  Eukaryotic Cell
   Internal membrane bound organelles

   Eukaryotic = “True nucleus”

   10-100 µm (micrometers) – larger than bacteria
       Largest single cell can be seen in bird eggs (ex. ostrich)


   Ex. Animals, plants, protists, fungi
Similarities
                  Similarities
   Membrane which separates internal components
    from the external environment

   Contain genetic material

   Contain ribosomes to make proteins

   Suspend materials in cytoplasm

   Carry out the same life processes
Animal Cell
Plant Cell
               Organelles
   Plasma membrane
   Cell wall (PLANTS ONLY)
   Nucleus
   Cytoplasm
   Endoplasmic Reticulum
   Ribosomes
   Golgi Complex
       Organelles Continued
   Lysosomes
   Mitochondria
   Chloroplasts (PLANTS ONLY)
   Microtubules/microfilaments
   Centrioles
   Cilia/flagella
   Vacuoles
                    Cell Wall
   Included in all plants and most bacteria

   Lies outside of plasma membrane

   Gives cell its shape and provides protection

   Plants have cell walls made of cellulose (source
    of fiber in our diets!)
   Has small openings to allow materials to pass to
    and from the cell membrane

   ANIMAL CELLS DO NOT HAVE CELL WALLS

   This is what Hooke observed in the mid-1600s
    with his microscope when observing cork cells
Plasma Membrane
                 Function
   Separates the cell from its surrounding
    environment

   Controls movement of materials into and
    out of the cell (selectively permeable)

   Keeps internal conditions constant by
    maintaining homeostasis
         Function Continued
   Signaling mechanism

   Used for making energy for the cell

   Used for cell to cell recognition

   Used to compartmentalize organelles
                      Structure
   Two Layers (bi-layer)
       Composed of:
           Lipids
           Proteins
           Carbohydrates
           Cholesterol


   “Fluid-like” – called the fluid mosaic model
                 Phospholipids
   Composed of:

       Two fatty acid chains

       Phosphate group

       Glycerol backbone
   Hydrophobic (non-polar) region
       “Hates” water
       Most important factor in the formation of
        membranes
       Fatty acid chain components

   Hydrophilic (polar) region
       “Loves” water
       Phosphate and glycerol components
                      Proteins
   Can be found:

       On the outer surface of membrane (glycoprotein)

       On the inner surface of membrane (peripheral)

       Extending through the membrane (trans-
        membrane or integral)
            Proteins Continued
   Function:
       Controls movement of substances through the
        membrane (transport)

       Acts as a receptor to signaling the cell to start or
        stop a metabolic activity (communication)

       Helps connect neighboring cells to each other or
        structural elements inside the cell (structure)
             Carbohydrates
   Linked to membrane proteins or lipids
    (glycoproteins or glycolipids)

   Branching from external surface of the
    membrane ONLY

   Used in cell recognition and signaling
                 Cholesterol

   Has hydrophobic and hydrophilic regions

   Helps prevent membranes from being too “fluid-
    like”

   Without cholesterol, cell membranes wouldn’t be
    firm enough and would be too permeable to some
    molecules
                   Nucleus
   Round, membrane-bound structure in
    Eukaryotic cells

   Serves as the control center for cell
    metabolism and reproduction

   Largest organelle
            Nucleus Continued
   Enclosed by the nuclear envelope

       Membrane surrounding the nucleus

       Double membrane

       Contains selectively permeable pores
            Nucleus Continued
   Contains chromatin

       DNA bound to various
        proteins

       Long, thin strands

       Make up chromosomes (hereditary material) by
        coiling tightly during cell division
            Nucleus Continued
   Within the nucleus is
    a nucleolus

       Dense, solid
        structure

       Site of ribosome
        production
                Cytoplasm
   Watery material within cell

   Contains dissolved materials for cell
    metabolism

   Chemical reactions in the cell occur here
    (metabolism)
       Cytoplasm Continued
   All organelles are suspended in this
    material
      Endoplasmic Reticulum
   System of fluid-filled canals

   Paths for the transport of materials
    throughout the cell

   Highly folded to increase the surface area
    for chemical reactions to occur
          Endoplasmic Reticulum
               Continued
   Can be connected to the nuclear envelope
    or free floating in the cytoplasm

   Rough ER
       Ribosomes are attached to the outer surface


   Smooth ER
       No ribosomes
                 Ribosomes
   Site of protein synthesis

   Found attached to the endoplasmic
    reticulum (rough ER) or in cytoplasm (free
    ribosomes)
               Golgi Complex
   Stacks of flattened membrane sacs

   Processes, packages and stores products being
    released from the cell

   Animal cells usually have only one, located near the
    nucleus

   Plant cells have several hundred (remember...they
    are the main producers in our food chain ! )
    Golgi Complex Continued
   Example:
      Proteins are produced by ribosomes on the rough ER



       These proteins are transported by the ER to the golgi

       Golgi process and package the proteins into vesicles

       Protein is transported to where it is needed in the
        cell, stored or sent to the plasma membrane to be
        sent out of the cell
                    Lysosomes
   Small, bubble-like structures surrounded by a single
    membrane (vesicle)
      Contain no water…so this allows it to have a
       single membrane

   Contains strong digestive acids

   In single-celled organisms:
      Involved in the digestion of food within the cell
          Lysosomes Continued
   In multicellular organisms:
       Breaks down worn-out cell organelles

       Part of the body’s defense against disease
          Ex. White blood cells




       Involved in developmental processes
          Ex. Tadpole  frog, digestion of its tail
                     Vacuoles
   Fluid filled organelles enclosed by a membrane

   Plant cells contain a single, large vacuole which
    occupies most of the space within a cell

       Used as a storage site (remember plants are
        producers and need to store all that energy in the
        form of sugar ! )
           Vacuoles Continued
   Animal cells:

       Very small and few in number

       Excess water is collected in contractile vacuoles
        (shaped like a star or sun)
                 Mitochondria
   Round or oval shaped


   Releases energy in food molecules for cell use
    (cellular respiration)


   “Powerhouse” of the cell
       Usually 300-800 per cell depending on cellular
        activity
        Mitochondria Continued
   Cells requiring lots of energy contain large numbers of
    mitochondria

       Ex. Muscle cells, heart cells

   Capable of moving independently throughout the cell

   Contain their own DNA and are capable of duplicating
    themselves
        Mitochondria Continued
   Surrounded by a double membrane

       Inner membrane is highly folded, forming cristae
        that extend into the middle of organelle

       Cristae provide a large surface area where
        biochemical reactions can occur
                      Plastids
   Membrane-enclosed organelles that are found only
    in photosynthetic, eukaryotic organisms

   ONLY IN PLANT CELLS (and some algae)

   Two types:
      Leucoplasts – colorless pigments

      Chromoplasts – colored pigments

         Most important is the chloroplast (green)
                    Chloroplasts
   Plastid containing a green pigment called
    chlorophyll

   Site of photosynthesis
       Food making process which uses light energy (autotrophic
        nutrition carried out by producers)


   Contains stacks of photosynthetic membranes
    called grana which contain chlorophyll
      Chloroplasts Continued

   Watery material that fills the remainder of
    the chloroplast is known as the stroma

   Contain their own DNA and have the ability
    to duplicate themselves
                     Microtubules
   Long, hollow, cylindrical structures found in the
    cytoplasm (made of protein)

   “Skeleton” for the cell, giving it its shape

   Used during cell division

   Found in:
       Centrioles
       Cilia
       Flagella
                Cilia & Flagella
   Hair-like organelles with the capacity for movement
       Single-celled organisms – cell movement
       Multicellular organisms – used to move
        substances over the cell’s surface

   Extends from the surface of cells

   Structures are identical but flagella are longer and
    fewer in number than cilia
                  Centrioles
   Found near the nucleus in animal cells

   Pair of cylindrical microtubules which lie at
    a right angle (90º) to each other

   Involved in cell division in animals cells
                   Microfilaments
   Long, solid, threadlike strands made of protein

   Associated with cell movement
       Ability to contract (ex. muscle cells)

       Involved in cytoplasm movement (ex. cytoplasmic
        streaming in ameoba)


   Serve as supporting structures for the cell
Origins of the Eukaryotic Cell

   The structural differences between eukaryotic
    and prokaryotic cells are so great, biologists
    have wondered how these two kinds of cells are
    related


   Most ideas are based on evidence that has
    been collected, called the endosymbiotic theory
   Eukaryotic cells are the result of:

       Endosymbiosis – condition in which one
        organism lives inside the cell of another
        organism to the benefit of both (mutualism)
   Mitochondria and chloroplasts are thought to be
    the result of bacteria which were engulfed by,
    then lived within, other larger cells

        Evidence – both contain their own DNA and can
         reproduce themselves like bacteria, similar in size
         to bacteria, have same metabolic machinery as
         bacteria

				
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posted:8/9/2012
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