Eukaryotic Cells - the basic plan.
"Eukaryotic cells come in an enormous variety of shape, form and function, but almost all eukaryotic cells share a common, basic construction plan. Separating the contents of the cell from its external environment is a plasma membrane, which acts as a very selective barrier, keeping wanted materials inside, and unwanted materials outside. Embedded within the membrane are specialized proteins, which allow the passage of needed molecules.
"Although interactions between the cell and the exterior take place by way of proteins embedded in the plasma membrane, there are specialized extensions, the cilia and flagella, which can be used to move the cells through the surrounding liquid, or move the liquid over the cells.
"Cells move in other ways as well. To move without the use of cilia or flagella, cells must change shape, and to change shape requires the force of shape changing molecules.
"Early microscopists saw that cells contained a fluid. The name for this fluid and the ideas about what it did changed quite a lot since the early years, but now it is recognized that interior of the cell is a complex, semifluid that functions as a reservoir of raw materials, and the site of a vast amount of macromolecular synthesis.
"Within the cytoplasm of each cell is a complex network of protein assemblies, the cytoskeleton, which plays many roles in transporting material around inside the cell, and providing structural support. Most of these elements are constructed of different types of proteins, each with its own special role to play.
"The part of the cell involved in protein synthesis is the endoplasmic reticulum (the "inside cell network") sometimes simply called the ER. The ER is a finely divided system of membrane-enclosed compartments with an interconnecting network of tubules.
"Most, but not all eukaryotic cells, plant and animal, contain a specialized internal membrane system called the Golgi apparatus. The major function of these organelles is to process and export of materials from cells and to make lysosomes, and other vacuoles.
"Mitochondria are small cytoplasmic organelles found in all eukaryotic cells that use oxygen in the release and conversion of energy. They contain a highly specialized and integrated system of enzymes and other proteins that progressively release energy from fuel molecules and convert it into a form that can be used for anabolism and movement.
"The largest and most clearly visible of the cell's constituents is the nucleus. Within the nucleus, DNA molecules, the cell's genetic machinery, are stored, repaired, transcribed and eventually replicated.
"Plant cells, in addition to all the other organelles found in eukaryotic cells, possess two other specialized cellular structures.
"The cell wall is a box-like layer of material synthesized by plant cells outside the plasma membrane. Hooke saw the cell walls of cork cells when he first looked through his microscope. Cellulose fibers form the basic skeletal foundations of cell walls.
"Plant cells can contain several different types of plastids. These are organelles such as the amyloplast, which is involved in starch storage, and chromoplasts which contain colored pigments.
"However the most easily recognizable plastid is the chloroplast, a green organelle that harvests light, then uses the trapped energy to synthesize sugar molecules, which are then stored as starch.
Cell Division - getting new cells from old cells.
"All living cells are produced by the division of pre-existing cells - this is the universal process of cell division. However, the mechanism of the division process is different in prokaryotic an eukaryotic cells.
"The cell division process in eukaryotic cells is often called Mitosis after the part of the cell cycle that can easily be seen taking place using a light microscope. It is a regularly repeating pattern of events that include the growth of the cell, the synthesis of new DNA molecules and then the packaging and delivery of these new chromosomes to the new daughter cells.