Protein function Flashcards
IgG
Two heavy chains (50kDa) and two light chains (kDa), cross-linked through disulfide bonding (covalent).
Domains of antibodies
Many beta sheets, built from one protein with smaller repeating domains.
Stabilising interaction with epitope
Hydrogen bonds and electrostatic forces, dependent on distance so much be close together.
Antibodies detect antigens directly ____ or following _____
ELISA, SDS-PAGE (western-blotting)
Enzyme linked immunosorbent assay
antibody bound to solid phase captures antigen, wash away rest of solution, label with another antibody with an enzyme linked to another protein (horseradish peroxidase) to product light.
Western blotting
Checks if epitope is present. Target proteins sit on membrane blot, and primary antibody bonds, then secondary antibody with an enzyme covalently attach or conjugated to a fluorophore instead!
Fluorescence
FITC (common fluorophore) many conjugated double bonds, excitation peak (270) excited into higher state then relaxes to release light at a longer wavelength (less energy)
Actin (microfilaments)
Globular bound ATP. reversible polymerises to filamentious actin to form ADP actin. Organised by actin binding proteins.
(-) is pointed
(+) is barbed
F-actin assembly
G-actin incorporates better in the (+) end through ATP hydrolysis, but capping can prevent this
Treadmilling of F-actin
Addition to the (+) end but removal from the (-) end to move, net no change in length, just position.
Microtubules (largest 250A)
Hollow, more rigid, target of anti-cancer drugs
Tubulin dimer assembly of MT
binds GTP for polymerisation, greater assembly at the (+) end.
Kinesins interacts with
Microtubules, using ATP to move trailing and leading head with attached cargo.
Intermediate filaments
Rope-like that lack polarity, coiled coils such as lamins and keratin. Insoluble and large for mechanical strength and shape.
IM formation
α-helices bonds to form a coiled coil dimer, aggregates to tetramer. Want to form because nonpolar residues are buried within.
Fibrous protein: collagen
Twisted braid of three extended chains - triple helix. Forms strong meshes (25% of proteins in the body)
Collagen triple helix structure
Glycine at every third residue (very small) fits in the centre of the helix.
gly-pro-hyp
Hydroxyproline
hydroxylated proline that allows for hydrogen bonding that stabilises the triple helix of collagen.
Hydroxylysine
allows for collagen chain cross-linking irreversibly, get harder more brittle - wrinkles, brittle bones.
Hydroxylase reaction
requires ascrobic acid for the reactions that make collagen strong - lack causes scurvy (bleeding gums, weak tissues)
Fibrous proteins: Elastin
Wet noodle with no shape but lysine cross-linking that connects the chains into a larger, rubbery structure.
Relaxed vs stretched state changes with physical forces.
Elastin importance
Degradation by elastase causes a stiff alveolar wall causing stiff lungs,. Elastase is inhibited by α1-antitrypsin but can be decreased by environmental/genetic factors (smoking).
