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MCAT Bio. Chem Ch. 3

Structural Proteins Compose the cytoskeleton, anchoring proteins, and much of the extracellular matrix
Most Common Structural Proteins Collagen, elastin, keratin, actin, and tubulin. These are generally fibrous in nature.
Motor Proteins Have one or more heads capable of force generation through a conformational charge. They have catalytic activity, and act as ATPases to power movement.
Most Common Applications Of Motor Proteins Muscle contraction, vesicle movement within cells, and cell motility are the most common applications of motor proteins.
Examples Of Motor Proteins Myosin, kinesin, and dynein
Binding Proteins Bind a specific substrate to either sequester it in the body or to hold its concentration at steady state.
Cell Adhesion Molecules (CAMs) Allow cells to bind to other cells or surfaces.
Cadherins Calcium-dependent glycoproteins that hold similar cells together.
Integrins Have two membrane-spanning chains and permit cells to adhere to proteins in the extracellular matrix. Some have signaling capabilities.
Selectins Allow cells to adhere to carbohydrates on the surfaces of other cells and are most commonly used in the immune system.
Antibodies / Immunoglobulins, Ig Used by the immune system to target a specific antigen, which may be a protein on the sufrace of a pathogen or a toxin
Two Regions Of Immunoglobulins A constant region, and a variable region.
Variable Region Of Immunoglobulins Responsible for antigen binding
How A Single Antibody Is Made Two identical heavy chains and two identical light chains form a single antibody, and are held together by disulfide linkages and noncovalent interactions.
Ion Channels Used for regulating ion flow into or out of a cell.
Ungated Channels Ion channels that are always open
Voltage-gated Channels Ion channels that are open within a range of membrane potentials.
Ligand-gated Channels Open in the presence of a specific binding substance (hormone or transmitter)
Enzyme-linked Receptors Participate in cell signalling through extracellular ligand binding and initiation of second messenger cascades
G Protein-Coupled Receptors Have a membrane-bound protein associated with a trimeric G protein, and also initiate second messenger systems.
Steps 1 & 2 Of How G Protein-Coupled Receptors Associate With G Protein 1. Ligand binding engages the protein. 2. GDP is replaced with GTP; the alpha-subunit dissociates from the Beta and Gamma subunits.
Steps 3 & 4 Of How G Protein-Coupled Receptors Associate With G Protein 3. The activated alpha-subunit alters the activity of adenylate cyclase or phospholipase C. 4. GTP is dephosphorylated to GDP, and the alpha-subunit rebinds to the Beta and Gamma subunits.
Electrophoresis Uses a gel matrix to observe the migration of proteins in response to an electric field.
Native PAGE Maintains the protein's shape, but results are difficult to compare because the mass-to-charge ratio differs for each protein.
SDS-PAGE Denatures the proteins and masks the native charge so that the comparison of size is more accurate, but the functional protein cannot be recaptured from the gel.
Isoelectric Focusing Separates proteins by their isoelectric point. The protein migrates towards an electrode until it reaches a region of the gel where pH = pI of the protein.
pI isoelectric point
Chromatography Separates protein mixtures on the basis of their affinity for a stationary phase or a mobile phase.
Column Chromatography Uses beads of a polar compound like silica or alumina (stationary phase) with a nonpolar solvent (mobile phase)
Ion-exchange Chromatography Uses a charged column and a variably saline eluent.
Size-exclusion Chromatography Relies on porous beads. Larger molecules elute first because they are not trapped in the small pores.
Affinity Chromatography Uses a bound receptor or ligand and an eluent with free ligand or a receptor for the protein of interest.
X-ray Crystallography Determines protein structure after the protein is isolated (though NMR can also be used)
Note On How Amino Acid Composition Can Be Determined By simple hydrolysis
Edman Degradation Sequential degradation that determines amino acid sequences
Note On How Activity Levels For Enzyme Samples Are Determined By following the process of a known reaction, often accompanied by a color change.
Note On How Protein Concentration Is Determined Colorimetrically by UV spectroscopy or through a color change reaction.
BCA Assay, Lowry Reagent Assay, and Bradford Protein Assay Each test for protein and have different advantages and disadvantages. Bradford protein assay involves a color change from brown-green to blue, is the most common.
Eq. 3.1: Migration Velocity v = Ez / f. v = migration velocity. E = Electric field strength. z = net charge on the molecule. f = frictional coefficient.
Created by: SamB91
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