Unit III. Cell Structure & Function


Cell- smallest unit of matter that is capable of performing the characteristics and function defined as life

  A. Cell Theory-

    1. All life is composed of cells

    2. All cells are the basic organizational unit of life

    3. All  cells come from other cells


Resource: Cells Alive. How big is a cell


  B. Early Scientists        

    1. Robert Hooke (1665)- first to describe a "cell". Used cork to identify tiny individual boxes

    2. Antonie van Leeuwenhoek (1673)- identified microorganisms in pond water; basic cellular structure

    3. Matthias Schleiden ( 1838) - stated that plants are multicellular organisms

    4. Theodor Schwann (1839)- stated animals are multicellular organisms

    5. Rudolf Virchow (1855)- examined cell reproduction in lower organisms


Notes: The Microscope


  C. Regions of the cell

    1. Cell membrane- the outer barrier of the cell

       * regulates the passage of molecules in and out of the cell

    2. Cytoplasm - semi fluid medium and components inside the cell

      a. organelles- small bodies within the cytoplasm which have individualized structures and functions

      b. cytosol- semi- fluid medium of dissolved organic matter which supports the organelles

    3. Nucleus - specialized organelle which contains the genetic matter


D.  Types of Cells

  1. Prokaryotic - "pre-nucleus" cell; doesn't contain a distinct nucleus

    - nucleoid region - region in cytoplasm where genetic information is found

      * Found primarily in the Monera Kingdom- Bacteria

  2. Eukaryotic- "true" nucleus' contains a distinct nucleus with nuclear membrane

     - most forms of life contain eukaryotic cells

    ** Reference to cells will pertain to eukaryotic cell unless mentioned


Image: Animal Cell

Image: Plant Cell

Resource: Cell Images. Scientific Illustrations


E. Parts of the Cell

  1. Cell membrane (Plasma membrane)  - fluid medium with the consistency of oil

    a. Components:

      1. Phospholipid bilayer:      Two layers oriented so non-polar tails point inward -- forming hydrophobic bonds

       * Glycolipids are occasionally found in the outer layer in the place of the phospholipids

         glycolipids- fat with two fatty acid chains and 1 sugar chain where the phosphate is usually found

         purpose- cell to cell recognition; different cells have different glycolipids                        

      2. Cholesterol: found in one layer which lends to stability of the lipid layer:  keeps the membrane

          fluid at lower temperatures

      3. Plant cells also contain an outer, thick layer that offers support for the plant cells called the cell wall.

         Bacterial cells also contains cell walls. Two exist: Gram positive & Gram negative.


Image: Cell Membrane & Proteins


      3. Proteins: either span the bilayer or found embedded in one single layer

        a. transport- transports most molecules in and out of the cell

           i.  channel - allows for straight passage of molecules or ions

           ii. carrier  -  bonds with molecules or ions to facilitate passage

        b. cell recognition

           i.  glycoprotein- finger prints the cell because of the sugar chain attached

        c. receptor protein- has specific shape to bond with certain molecules (hormones) which cause a

            certain chemical reaction within the cell

        d. cell adhesion - bonds particular cells together

        e. attachment - bonds filaments of the cytoplasm to the cell membrane

        f.  enzymatic- perform chemical reactions with membrane and cytoplasm

        g. more of which have to be explored (?)


    b. Fluid- Mosaic Model - term used to describe the appearance and function of the cell membrane

      1. phospholipids, glycolipids and cholesterol all assist in producing a fluid characteristic

         - molecules can move...

      2. proteins, glycolipids and cholesterol give the mosaic pattern


    c.  Membrane characteristics

      1. selectively permeable- characteristic where membrane regulates the passage of particles

        a. diffusion- movement of particles from an area of higher concentration to an area of lower concentration.

           net movement- movement which changes concentrations

        b. factors that affect diffusion

           i. particle size and shape

           ii. temperature

           iii. concentration gradient- difference in concentrations

           iv. cytoplasmic streaming- continuous movement of materials in cytoplasm


    d. diffusion in membranes

      1. facilitated diffusion- using a protein to move particles down the conc. gradient

      2. active transport- using a protein to move particles up the conc. gradient

         *requires energy -  ATP - adenosine triphosphate

         pump- proteins that use active transport to move particles between interior and exterior of cell

         ex. Na+/K+ pump: Used to move sodium & potassium ions across nerve membranes

      3. osmosis - diffusion of water across a selectively permeable membrane

        - water moves from an area of high water conc.(low solute) to an area of low water conc. (high solute)                

        -osmotic pressure - internal pressure due to net movement of water into

      4. osmotic conditions: cell concentration vs. environmental solution conc.

          a. isotonic- solute conc. inside is the same as outside-- no net movement  of water

             animal cell normal               plant cell -  flaccid

          b. hypotonic- solute conc. outside is less than cell conc.

             animal cell- lysed                   plant cell   - turgid

          c. hypertonic- solute conc. outside is greater than cell conc.

             animal cell crenated            plant cell -   plasmolyzed


    e movement of particles larger than transport proteins

      1. endocytosis- cell membrane indents around molecules and forms a vesicle

          a. pinocytosis- uptaking fluid molecules

          b. phagocytosis- uptaking solid molecules

      2. exocytosis- vesicles fuse with cell membrane and release materials

Resources for animal cells: Cells Alive, Animal Cell 2, Cell Structures & Processes

Resource for Plant Cells: Cells Alive ,

Resource: Cells Alive. Bacterial Cell


  2. Cytoplasm- the region of the cell inside the cell membrane

    a. cytosol- solution

      - contains amino acids, monosaccharides, water and other essential molecules

        (All basic building blocks for the macromolecules)

    b. Organelles - membraned bodies housed within the cell: Each has a specialized design and function

      1. Ribsome- organelle having 2 subunits made from proteins which function to produce proteins. Resource

         a. "free"- found suspended in cytosol

         b. "bound"- found attached to endoplasmic reticulum

     Membranous canals and vacuoles

       2. Endoplasmic reticulum- membraned canals that connect the nucleus with the cell membrane   

           a. "rough" - contains ribosomes on outer membrane surface

             - responsible for assistance in protein synthesis and transport to exterior of the cell

           b. "smooth" - no ribosomes; but contains specialized enzymes

             -various functions depending upon location in the body

             -lipid biosynthesis, carbohydrate metabolism, detoxification of drugs

       3. Golgi Apparatus- similar in appearance to smooth E.R.

          - works in conjunction with the E.R. where it modifies, stores and routes products of the E.R. Image          

          - uses vesicles to transport molecules between E.R., Golgi and other parts

      4. vesicle- membrane storage compartment used in endo & exocytosis mechanism

      5. Vacuole- membraned organelle used primarily for storage

         a. food vacuoles - store food for reserve usage's

         b. contractile vacuole- stores water and pumps out excess when necessary

         c. central vacuole- plant vacuole which has a variety of functions

            - stores molecules, deposit for metabolism by-products, contain pigments

      6. Lysosomes- "suicide organelles"- membrane bound organelles that contain enzymes whose

         responsibilities are macromolecule and organelle digestion

         - formed from the Golgi apparatus

        -Peroxisomes- Lysosomes that contain oxidizing enzymes that are not made from the Golgi

     Energy-related organelles

      7.  Mitochondria- double membraned organelle that is responsible for respiration

      8. Plastid- organelle found in plants that are responsible for food production (carbohydrates)

        - chloroplasts- plastids which contain chlorophyll


  3.  Cytoskeleton- scaffolding structure of the cytoplasm (mesh netting)

    - maintains cell's shape, anchors organelles, allows cell and contents to move within cell

    a. consists of 3 different protein tubules

        1. microtubules- largest- usually in the form of  cilia and flagella & also moves organelles

        2. intermediate filaments- assistance in cell division ( cleavage furrow)

        3. microfilaments- smallest- assists in support of the cell

    b. Cytoskeleton extensions

        1. cilia & flagella- these are protein extensions that provide movement for the cells

           -image: cilia & flagella movement

        2. junctions- proteins provide attachment, structure and communication between cells.

           -Resource: junctions


  4. Nucleus    

     - double membraned organelle which contains chromosomal material

    a. Components

      1. nuclear envelope ( membrane)- double membrane which surrounds the nucleus & is continuous

         with the endoplasmic reticulum

        -nuclear pores- holes in the envelope formed from embedded protein which allow certain molecules to pass

         from cytoplasm to nucleoplasm

      2. nucleolus- dense area which function in the synthesis of ribosomes                

      3. chromatin- regions where genetic material is found

        - long chains of DNA molecules -- Deoxyribonucleic acids

        -chromosome - condensed chromatin


F. Cell Division & Mitosis

  1. DNA replication- production of identical DNA double helices

    a. Binary Fission- (Asexual reproduction)-  Prokaryotic organisms

    b. Eukaryotic cell division (Asexual repro of single-celled Eukaryotes)

      1. chromosome structure

         a. chromatin-       histone 

         b. chromosome

            -homologous chromosome



            -sister chromatids

            -karyotype- 46 chromosomes- 23 pairs

    c. Cell Cycle. animation

      1. parent cell

      2. daughter cell

      3. 5 phases: G1 - S - G2 - M - C

         Interphase  (G1 -S - G2)

         a. G1 -  (Primary Growth Phase) a.k.a. (G = gap)

         b. S -   (Genome Synthesis, DNA replication)

         c. G2 - (Secondary Growth Phase)

         d.  M- (Mitosis) - 4 stages. animation

            i. prophase-   centrioles, poles, spindle fibers, asters

            ii. metaphase- equator (metaphase plate)

            iii. anaphase

            iv. telophase

            v. Cytokinesis ( C)                                                                            

                -animal cells- cleavage furrow

                -plant cells - cell plate

   **The 5 phases are sometimes condensed to IPMAT, where interphase is the time between daughter cell formations.



osmosis image: http://www.hayloes.com/Ess/EssLessCell01/index.html