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MCAT Bio. Chem Ch. 3
| Question | Answer |
|---|---|
| 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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