Biochem quiz 1 He/Myoglobin Flashcards
What is the function of Myoglobin?
oxygen carrier in muscle cells, stores O2 in muscles, binds oxygen at low O2 levels
What is the function of Hemeglobin?
oxygen carrier in the blood, binds o2 in the lungs, releases o2 in the tissues. VERY sensitive to small changes in O2, carries co2 from tissues to lungs.
What does the structure of He look like?
porphyrin ring with a singe Fe atom
How many bonds can Fe form?
6
What type of Fe cannot bind to He?
Fe3+(HbMEt) cannot bind to O2. Only Fe2+ can bind to O2.
How many binding sites does myoglobin have?
1 O2 binding site , one single polypeptide chain that contains 1 heme and binds to 1 O2
How many binding sites does He have?
He has 4 binding sites , 4 polypeptide chains with 1 heme each capable of binding 1 O2
What type of cooperativity does Hb display and why?
Positive cooperativity, receptor occupancy is more receptive to change with positive coop. sigmoid shaped curve, higher affinity as curve moves to the left.
What type of cooperativity does Myo. display and why?
Non - cooperative because it is less sensitive to changes to ligand binding. ( less affinity to oxygen)
what are primary features of positive cooperativity?
more than 2 binding sites,receptor confirmations have different affinities for the ligand. first ligand bound has lower affinity(Larger KD) than subsequent ligands bound.
T, taut HB state factors:
Low affinity for O2, prevalent at low O2 in tissues
R relaxed HB state factors:
higher affinity for O2, prevalent at high O2 in lungs
How does the presence of O2 affect T/R confirmation?
Without O2 bound to Hb, Fe is out of the heme plane and T confirmation is stabilized. When O2 is bound, the Fe is pulled back to the heme plane, R confirmation is stabilized, and high affinity binding at the other O2 binding sites occur.
how does ligand binding affect positive cooperativity?
When ligand is not bound, there is low affinity, when ligand binds to site, becomes high affinity ( must have 2+ binding sites)
How does O2 act as an allosteric modifier?
When O2 binds to one of its 4 sites in Hb, the oxygen at the other sites increase to bind quicker to oxygen . O2 is a homotropic allosteric modifier because it binds to the active site.
How are heterotropic allosteric modifiers different from homotropic?
they are different from the ligand at the active site .
inhibitors stabilize the inactive form and activators stabilize the active form of the active site. Hetero- when ligand binding at one site influences the binding at a different site.
List the heterotropic allosteric modifiers :
bpg 3, co2, ph (H+) all are heterotropic inhibitors
How does H+ inhibit the binding of O2 to Hb?
increasing H+ = decreasing pH, DECREASES the amount of O2 bound to Hb. When H+ decreases and pH increases, the R state becomes more stable.
what type of bond does Co2 form with the terminal amine group of Hb?
covalent bond that releases H+ and stabilizes the T state
How does BPG decrease affinity for O2 in Hb?
BPG stabilizes the t state by binding at a site distant from the O2 binding site.
why does HbF have a higher affinity to oxygen than HbA?
HbF does not bind well to BPG( has lower affinity to BPG), has a MUCH higher affinity to oxygen than most common HbA.
what is thalassemias
impaired synthesis of alpha or beta chains, complete lack of alpha chains usually fatal
sickle cell anemia
glu–> val mutation, HbS forms insoluble fibers, gives proteins sickle cell shape
what factors increase affinity for O2?
O2 and CO binding to the active site increase affinity for O2
does the first ligand bound have a higher or lower affinity in positive cooperativity?
Lower affinity , t state, higher KD than subsequent ligands bound
why is O2 a homotropic allosteric modifier?
It binds to the actual active site of the ligand
how does O2 bind to Hb?
02 binds to heme iron through a coordinate bond with the proximal histidine.
myoglobin has a _______ affinity to oxygen than Hemoglobin.
HIGHER
what biochemical property is unique to the allosteric modulation of Hb?
C02 reversibly stabilizes the T confirmation. Co2 has allosteric affects. Competes with Oxygen, and when it binds, it allows other sites to have a higher affinity for oxygen. Overall, increases affinity for oxygen.
what feature of fetal hemoglobin facilitates delivery of O2 from the maternal HbA to HbF?
HbF has a lower affinity for BPG than HbA. HbF has a higher affinity for oxygen than HbA
heterotropic modifiers _______________
lower affinity of Hb to O2
large Kd=________ affinity
lower affinity
CO stabilizes the ______confirmation
R . binds at active site and has higher affinity to O2, binds very tightly and competes with O2- why it is deadly
