S t r u c t u r e   &   O r g a n i z a t i o n :     L e c t u r e  # 6 Vocabulary | Study Questions
Eukaryotic Cell Structure
Objectives:
  1. Understand the basic structure and function of the major subcellular structures associated with eukaryotic cells.
  2. Become familiar with some basic theories concerning the origin of eukaryotic cell.
  1. Structure of the eukaryotic cell
    (Remember: the cell is the basic structural and functional unit of your life.)
    1. Cell coverings
      1. Cell walls
        (Review) Plants (cellulose) & fungi (chitin). In the electron micrograph, we see the cell wall, and pressed up against it (by the cytoplasm) is the plasma membrane. Cellulose microfibrils (tiny fibers) function to hold the plant up. the function of the cell wall is structure: support.
      2. Plasma membrane
        All cells. (In our case, the outer covering of our cells.) Phospholipid bilayer, cholesterol (to prevent tbe phospholipids from packing too tightly), proteins (transport, etc..). There is no bonding between phospholipids--it's held together/ organized according to its hydorphobic and hydrophilic ends.
        When a carbohydrate is attached to a protein, it's called a glycoprotein.
        The functions of plasma membrane: 1) as a boundary layer 2) differential permeability: able to determine what can/ cannot cross into the cell (it is selectively permeable).
    2. Cell matrix: the cytoplasm
      The area between the nucleus and the cell membrane. (Like jello with fruit organelles.) Functions in 1) maintaining the internal cellular environment: water content, pH, salt content, etc.. 2) a reservoir of materials: (e.g. amino acids (from hydrolysis-ized proteins we've eaten) for incorporation into proteins, etc.).
    3. Cytoskeleton
      1. Structure
        Two major components are microtubules (protein tubes) and microfilaments (strands and rods of protein). Form a network structure throughout the interior of the cell.
      2. Function
        1) to maintain cell structure, 2) to organize organelles to optimize chemical reactions (e.g. microfilaments will move chloroplasts to optimally gather sunlight. Microtubules are important in moving chromosomes around during cell division).
    4. Subcellular organelles
      Representative diagrams
      Subcellular structures; structures found within cells. Carry out the functions of the cell (division of labor).
      1. Nucleus
        1. Structure
          One of the three double-membrane structures we will be discussing here (the other two: mitochondria, chloroplasts) Within the membrane is found the nucleoplasm, where we find the chromosomes.
        2. Function
          The nucleus is the control center of the cell. The outer and inner membranes are pourous to allow transport.
      2. Nucleolus
        Found within the nucleus (the dark spot in photos, diagrams).
        1. Structure
        2. Function
          Manufacturing and assembling the protein subunits (2) of ribosomes. Also, rRNA (ribosomal RNA) is produced in the nucleolus.)
      3. Endoplasmic reticulum
        Rough ER (Endoplasmic Reticulum) and smooth ER.
        1. Structure
          Single-membrane. Rough ER (Endoplasmic Reticulum) is studded with ribosomes, smooth ER is not.
        2. Function
          1) to transport materials (transport system) 2) important in the synthesis of lipids. (The ribosomes embedded in the Rough ER function in protein synthesis.) Smooth ER functions in drug detoxification.
      4. Golgi apparatus
        Another part of the cellular transport system. Common where there is a lot of cell activity.
        1. Structure
          A single-membrane system, consisting of layers (stacked pancake-like).
        2. Function
          Transports of material 2) modifies and package materials in transport vesicles which pinch off and move into the cytoplasm. (The vesicles are primarily moved by diffusion.) Note the summary diagram.
          A lysosome is a vesicle with hydrolytic enzymes (hydrolysis) that breaks down chemicals.
      5. Mitochondria
        1. Structure
          Double-membrane structure. An outer membrane and an inner membrane (folded to increase surface area.)
        2. Function
          To make ATP (cellular respiration).
      6. Chloroplasts
        (a plastid)
        1. Structure
          Double-membrane structure. Contains grana, where the light reaction of photosynthesis occurs. The area in between the grana is the stroma, where the dark (light-independent) reaction occurs.
        2. Function
          Photosynthesis! Photosynthesis! Photosynthesis! Life!
      7. Vacuoles
        1. Structure
          Single-membrane sack-like structure.
        2. Function
          1) Storage of materials: waste products, useful products, 2) important in determining cell size, 3) important in maintaining cell environment.
      8. Ribosomes
        1. Structure
          Made of two subunit proteins.
        2. Function
          Making proteins: protein synthesis! (lecture 9)
  2. The origin of eukaryotic structures
    These theories have to do with cell membranes of the organelles: whether they are single or double.
    1. Endosymbiotic theory
    2. Definition: This theory suggests that the mitochondria and chloroplasts originate from a symbioitc relationship between two cells, where one lived within the other, and both benefitted from the relationship.
      'Endo' means within, and 'symbiosis' means to live as one: endosymbiotic theory relates to the mitochondria and chloroplasts, stating that they may have originated as prokaryotes that were engulfed and used by eukaryotes, eventually becoming integrated as a part of the eukaryotic cell itself.
      1. Evidence:
        1) Mitochondria and chloroplasts contain a single, circular chromosome
        2) Mitochondria and chloroplasts contain prokaryotic-like ribosomes and synthesize proteins.
        3) Mitochondria and chloroplasts grow, duplicate their DNA, and reproduce (similar to binary fission in prokaryotes).
        4) Surrounded by 2 separate membranes: inner membrane resembles prokaryotic membrane, outer membrane resembles a eukaryotic membrane.
      2. Examples: An amoeba lacks mitochondria; houses aerobic bacteria
        Corals, some clams, & a few snails: house bacteria
        In other words, bacteria live within these organisms and are vital to their survival (they provide the energy): they have a symbiotic relationship.
    3. Autogenous theory
      "Self-production" due to membrane folding back upon itself: ER, Golgi apparatus, double-membrane of nucleus (both membranes are eukaryotic-typical, as opposed to the double-membrane stuctures discussed under the endosymbiotic theory), etc..
      1. Definition: This theory addresses the origin of the other (single) membrane-bound organelles.

        2. Evidence:

        Specialization of internal cell membranes led to single-membrane bound organelles (ER, Golgi, etc..).

        AIR POLUTION and cells:
        The Wasatch Front (Ogden-SLC-Provo) ranks third in U.S. air pollution. Air pollution effects cells:
        Mechanisms of Damage

        Costs Incurred Due To The Adverse Effects of Air Pollution