4.5 Quaternary Structure Flashcards
what is quaternary structure
final level of protein, consisting of +1 polypeptide chain
how do the chains interact, which bonds
noncavalently via electrostatic attractions, H2 bonding and hydrophobic interaxns
what is allosteric
when changes in structure at one site causes changes in properties at distant site
what is hemoglobin
allosteric globular tetramer; 2 alpha chains and 2 beta chains
describe the chains in hemoglobin
a-chain is 141 residue long, b-chain is 146. many aa in chains are homologous. heme is same as myoglobin
what is homologous
same aa residues in the same position
how many oxygen binds to one hemglobin
4 molecules of oxygen
difference btwn oxygen binding of hemoglobin and myoglobin
both bind O2 reversibly but only hemoglobin exhibits positive coopereativity
what is positive cooperativity
when one O2 molecule binds, next one becomes easier to bind. bindng of first facilitates binding of second and so forth
shape of oxygen-binfing curve of myoglobin
hyperbolic
shape of oxygen-binfing curve of hemoglobin
sigmoidal
differenece btwn saturation of hemoglobin and myoglobin
hemoglobin’s binding curve is lower than myoglobin at any O2 pressure; myoglobin has higher % of saturation than hemoglobin
what is the fn of myoglobin
02 storage in muscle, bind strongly to 02 at lower pressures, 50% saturated at 1 torr
what is the fn of hemoglobin
O2 transport, bind strongly and release easily. in alveoli O2 poresure is 100 torr, hemoglobin 100% saturated. in capillaries of muscles pressure is 20 torr, less than 50% saturated with O2
describe confromational changes in hemoglobin
structural changes during binding is characteristic of allosteric proteins. has diff 4* structure in bound (oxygenated) and unbond forms. 2 beta chains closer in oxygenated form
