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Dr. W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)

9/7/99 Text (7th ed.): Ch. 2, pp. 23-32; Ch. 6, pp. 138-147

possible web site: http://www.cellsalive.com (images of both cells and bacteria)

possible HVCC a/v resource: video: VT 1593"Cell Biology" (to be seen in recitation)


1. Cells are the basic units of life. Cells can function as individual organisms or can be part of higher organizational units. two major types of cells: prokaryotic and eukaryotic. Prokaryotic cells (e.g., bacteria) have neither nucleus ( their DNA is unbound) nor specialized organelles (specialized membrane-bound structures that perform different functions). Eukaryotic cells have three basic parts:

  1. plasma membrane as an outer boundary
  2. nucleus containing the genetic material within its own membrane
  3. cytoplasm, the material within the plasma membrane and outside of the nuclear envelope. The outer layer of cytoplasm is in a gel state and called ectoplasm, and the more fluid inner is called endoplasm.

Single cells are small, since these organisms need lots of surface area for diffusion and other processes, but a small volume for the nucleus to control all of the cytoplasm.

2. Cell membranes. "Fluid-mosaic" model of phospholipid bilayer. Membranes are fluid and constantly changing. A phospholipid has a polar (charged) phosphate end and a nonpolar (uncharged) lipid end. Two layers of phospholipids are oriented so that the"oily," hydrophobic lipid ends are sandwiched between the hydrophilic phosphate ends. This allows the controlled passage of material and to define inside from outside. Cholesterol can be found wedged in the hydrophobic portion, helping to make the membrane less permeable and more rigid. There are protein"icebergs" floating in the bilayer: extrinsic or outer/inner proteins and intrinsic embedded proteins. Finally, the glycocalyx is made of surface carbohydrates: cell recognition.

  1. Nucleus, surrounded by the nuclear envelope, also contains the nucleolus. It is the control and information center of the cell. It directs the types of biochemical activities that go on inside the cell, and also acts as the repository of information, storing genetic material and information for the next generation. Nuclear pores in the envelope are too small to let DNA out, but do let the nucleus to be in contact with the endoplasmic reticulum.1 DNA is usually not by itself, but combined with protein. When not dividing, this DNA/protein combination is known as chromatin, and during division, it forms thread-like chromosomes.
  2. Nucleolus, also in the nucleus, contains RNA and proteins, to make ribosomes (sites of protein synthesis).
  3. Ribosome, containing both rRNA and proteins, can be free floating or attached to endoplasmic reticulum. They are usually grouped in clusters called polyribosomes, as they are linked with mRNA (messenger RNA).
  4. Endoplasmic reticulum (ER), a series of membrane tubes and sheets throughout the cytoplasm that functions in communication and storage. Can either be rough ER with ribosomes attached or smooth ER without.
  5. Golgi apparatus, associated with ER in the cytoplasm, for packaging and export of materials. A stack of membranes that can package and secrete, among other things, glycoproteins for the plasma membrane and lysosomes.
  6. Lysosomes, in the cytoplasm, are membrane-surrounded pockets of digestive enzymes. These enzymes (acid hydrolases) are synthesized into the ER, then get packaged up and made into lysosomes by the Golgi apparatus. Lysosomes can help break down food vesicles or can be used to recycle the cell's contents.
  7. Mitochondria (-ion, singular), in cytoplasm, are the power sources for the cell. We will talk about the reactions that make energy after Thanksgiving, but I hope that cellular respiration and ATP ring a bell. Mitochondria are double-membraned. The inner membrane is highly folded for more surface area for energy-producing reactions.
  8. Cytoskeleton, or lattice-like network of filaments throughout the cell for support.
  9. Centrioles. Centrioles are microtubule structures that assist in cell division in animal cells.
  10. Flagella and cilia. Both are membrane-bound cylinders that contain sets of microtubules, and move as a result of microtubule doublets sliding along each other.

Tissue: a group of similar cells specialized for the purpose of a common function. There are four animal tissue types.

  1. Epithelial tissue generally covers or lines something, and is usually separated from underlying tissues by a basement membrane. Usually see flat cells, frequently renewed, with surface specializations. Examples: skin (protection); absorption (lining of intestines)
  2. Connective tissues support and bind other tissues together. CT contains cells and fibers in an extracellular matrix (ground substance). Connective tissues can be either loose, like the aleolar connective tissue underneath the dermis of your skin, or fibrous, densely packed as in tendons and ligaments. Other types of connective tissues include adipose, a loose connective tissue with large fat cells; cartilage, with cartilage cells in a secreted rubbery matrix vs. bone, with bone cells in a calcium phosphate matrix.
  3. Muscle tissue allows movement. There is smooth muscle in the gut, cardiac muscle in the heart, and striated muscle under voluntary control in your limbs. Muscles work by contraction via the action of actin and myosin.
  4. Nervous tissue, made of neurons, is for communication.: a neuron with an axon and dendrites works by conducting electrical impulses, and is often sheathed in myelin. Organs, systems, and organisms are the next levels of organization!

1 CP Hickman et al., Biology of Animals, 7th ed. (WCB McGraw-Hill, Boston, 1998), p. 28.


|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|


Please send comments and questions to: cronewil@hvcc.edu


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This page updated on September 15, 1999