summer BICH exam 1

how many oxygens do myoglobin bingd?

one molecule Oxygen

how many oxygens foes hemoglobin bind ?

4 molecules of oxygen

where is myoglobin located ?

in the muscle

what is the function of myoglobin ?

oxygen storage, binds O2 when not needed by tissues, releases it when necessary

what is the structure of myoglobin consists of ?

single polypeptide chain with 1 heme ground

what is the shape of myoglobin O2 binding curve ?

hyperbolic

what does a hyperbolic shaped curve indicate ?

high affinity, doesn’t easily give up oxygen

where is hemoglobin located at ?

red blood cells

what is the function of hemoglobin

transport of oxygen from lungs to tissue, binds O2 in lungs nad releases it in tissue

what is the structure of hemoglobin ?

tetramer and 4 heme group

what does deoxyhemoglobin mean

it menas there is low affinity and it has a low oxygen state

what does oxyhemoglobin mean

high affinity, saturated with oxygen

what is a heme

a prosthetic group with a protoporphyring ring and a ferrous iron that binds O2 in Mb and Hb

what is Myoglobin heme group ?

protoporphyrin ring with ferrous iron bound

what is structure like?

spherical ( globular), contains 8 helices, bends between helices

what is the role of iron in heme

Iron ( fe2+) binds oxygen and is coordinated by 4 nitrogens of the porphyrin rings, one from proximal His, and optionally one from oxygen

what type of proteins are Mb and Hb?

globular proteins that reversibly bind oxygen

what is the hill coefficeint (n) for Mb?

n=1 ( non-cooperative binding)

how many subunits and heme groups does Hb have ?

4 subunits ( 2 a, 2b) and 4 heme groups

what is the Hill coefficeint (n) for Hb?

n=3 ( positive cooperativity)

what is p50?

the partial pressure O2 at which the protein is 50% saturated

what does a lower p50 mean ?

higher affinity for oxygen

which has lower p50 Mb or Hb?

Mb ( Mb=2.8 torr , Hb=26torr )

what is Mb p50 value ?

2.8 torr

what is Hb P50 value ?

26 torr

what is the dissociation constant (kd)

the concentration of ligand at which half of the proteins binding site are occupied

what is the relationship between Kd and affinity ?

inverse- lower Kd= higher affinity

why is CO dangerous >

Co binds to heem 200x stronger than O2 blocking oxygen binding

what structural feature of Mb/Hb helps reduce CO binding ?

distal histidine ( His E7) causes steric hindrance, favoring angled binding of O2

what is the Hill equation used >

describes cooperative binding and helps calculate P50 and the Hill coefficient (n)

if N>1 in the Hill equation, what does that indicate?

positive cooperatively ( ie Hb)

what is the order of event based on structural changes occuring for oxygen binding in the first subunit of Hb?

1. movement of iron into the pane of the protoporhyrin ring

2. HisF8 relocates

3. movement of helix F

4. breaking of hydrophilic between dimers

5. 15* rotation collapse of central cavity