Ch 3 - Nonenzymatic Protein Function and Protein Analysis Flashcards
What do structural proteins compose? What are the most common?
- compose the cytoskeleton, anchoring proteins, and much of the extracellular matrix
- collagen, elastin, keratin, actin, and tubulin
- generally fibrous in nature
What are the motor proteins?
- have one or more heads capable of force generation through a conformational change
- have catalytic activity, acting as ATPases to power movement
What are the most common applications of motor proteins?
- muscle contraction, vesicle movement within cells, and cell motility
- myosin, kinesin, and dynein
What to binding proteins bind?
bind a specific substrate, either to sequester it in the body or hold its concentration at steady state
What do cell adhesion molecules (CAM) allow?
cells to bind to other cells or surfaces
What is the difference between cadherins, integrins, and selectins?
- cadherins: calcium dependent glycoproteins that hold similar cells together
- integrins: have 2 membrane-spanning chains and permit cells to adhere to proteins in the ECM (some also have signaling capabilities)
- selectins: allow cells to adhere to carbohydrates on the surface of other cells and are most commonly used in the immune system
How are antibodies used by the immune system?
- or immunoglobulins, Ig
- used to target a specific antigen, which may be a protein on the surface of a pathogen (invading organism) or a toxin
What are the 2 regions within immunoglobulins?
- a constant region and a variable region
- variable responsible for antigen binding
What chains form antibodies and what holds them together?
- 2 identical heavy chains and 2 identical light chains form a single antibody
- they are held together by disulfide linkages and non covalent interactions
What are ion channels used for?
used for regulating ion flow in or out of the cell
What are the 3 types of ion channels?
- ungated: always open
- voltage-gated: open within range of membrane potentials
- ligand-gated: open in the presence of a specific binding substance, usually a hormone or neurotransmitter
What role to enzyme-linked receptors play in cell signaling?
through extracellular ligand binding and initiation of second messenger cascades
What re G protein-coupled receptors?
- have a membrane-bound protein associated with a trimeric G protein and they also initiate the second messenger systems
What engages G protein?
ligand binding
What is electrophoresis?
uses a gel matrix to observe the migration of proteins in response to an electric field
What is the difference between Native PAGE, SDS PAGE, and isoelectric focusing?
- native: maintains the proteins shape, but results are difficult to compare because the mass-to-charge ratio differs for each protein
- sds: denatures the proteins and masks the native charge so that comparison of size is more accurate, but the functional protein cannot be recaptured from the gel
- isoelectric: separates proteins by their pI; the protein migrates toward an electrode until it reaches a region of the gel where pH = pI of the protein
What is chromatography?
separates protein mixtures on the basis of their affinity for a stationary phase or a mobile phase
- all are about the affinity of a substance for the mobile and stationary phases except for size-exclusion
What is the difference between column, ion-exchange, size-exclusion, and affinity chromatography?
- column: uses beads of a polar compound (stationary phase) with a non polar solvent (mobile)
- ion exchange: uses a charged column and a variably saline eluent
- size: relies on porous beads (larger molecules elute first because they are not trapped in the small pores)
- affinity: uses a bound receptor or ligand and an eluent with free ligand or a receptor for the protein of interest
What primarily determines protein structure/
Xray crystallography after the protein is isolated, although NMR can also be used
How can amino acid composition be determined?
by simply hydrolysis, but amino acid sequencing requires sequential degradation, such as Edman degradation (proceeds from the amino N terminus)
How are activity levels of enzymatic samples determined?
by following the process of a known reaction, often accompanied by a color change
How are protein concentrations determined colorimetrically?
either by UV spectroscopy or through color change reaction
- BCA assay, Lowry reagent assay, Bradford protein assay (most common) each test for protein and have advantages/disadvantages
What are the functions of the heterotrimeric G proteins?
- Gs: stimulates
- Gi: inhibits
- Gq: activates phospholipase C
How do cytoskeletal proteins differ from motor proteins?
- cyto: tend to be fibrous with repeating domains
- motor: tend to have ATPase activity and binding heads
- both have protein functions in cellular motility
