1/22/03 - Post-class outline

Learning objectives:

• Basic cellular structure
• lipid-containing membranes surround cells
• the interior fluid is called cytoplasm
• membranes control the movement of materials into and out of the cell
• cells also have a variety of intracellular membrane-bound organelles
• nucleus
• mitochondria
• endomembrane system, including endoplasmic reticulum
• Skeletal muscle cell structure
• muscles are unusual cells
• very large
• multinucleated
• contain very orderly arrays of "contractile filaments"
• contain large amounts of modified endoplasmic reticulum, called sarcoplasmic reticulum.
• contractile filaments are made of the filamentous proteins actin and myosin
• Basic protein structure
• Proteins are composed of amino acids linked together in a linear chain
• There are 20 different amino acids with different chemical properties
• electrical charge
• size
• hydropathy
• hydrophilic molecules are chemically and energetically stable in contact with water and thus associate easily with the aqueous (water) environment of the cell cytoplasm.
• hydrophobic molecules (i.e. lipids such as fats and oils) are not energetically stable in contact with water and are more stable in contact with other hydrophobic molecules.  These molecules tend to orient away from the cytoplasm and become buried into the interior of a protein.
• Levels of protein structure
• primary - linear sequence of amino acids, this largely dictates the other levels of structure.
• secondary - simple 3-D features such as alpha coils and beta sheets.
• tertiary - the entire 3-D structure.
• quaternary - the association of separate proteins (subunits) together to form a functional unit.
• Protein 3-D structure depends largely on the primary sequence of amino acids.
• The 3-D structure of proteins can change, and this is how proteins accomplish many of their functions.
• Interactions with other molecules can change the 3-D shape of proteins, this is largely how proteins are regulated.
• The contractile filaments
• Arrangement of actin and myosin into thin (actin) and thick (myosin) filaments. 
• The sliding filament theory says that the filaments do not change in length themselves, but instead that they slide past each other.
• The "ratchet" mechanism for actin / myosin sliding.  This is an example of a structural/locomotory role for proteins.
• The role of adenosine triphosphate (ATP) in the sliding process.  This is an example of an enzymatic role of proteins.  Here myosin is acting as an enzyme by catalyzing the reaction of ATP to ADP (adenosine diphosphate) and P (phosphate), and capturing the energy that was present in the chemical bond that is broken in the process.