Biochem quiz 1 He/Myoglobin

Question 1

What is the function of Myoglobin?

Answer 1

oxygen carrier in muscle cells, stores O2 in muscles, binds oxygen at low O2 levels

Question 2

What is the function of Hemeglobin?

Answer 2

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.

Question 3

What does the structure of He look like?

Answer 3

porphyrin ring with a singe Fe atom

Question 4

How many bonds can Fe form?

Answer 4

6

Question 5

What type of Fe cannot bind to He?

Answer 5

Fe3+(HbMEt) cannot bind to O2. Only Fe2+ can bind to O2.

Question 6

How many binding sites does myoglobin have?

Answer 6

1 O2 binding site , one single polypeptide chain that contains 1 heme and binds to 1 O2

Question 7

How many binding sites does He have?

Answer 7

He has 4 binding sites , 4 polypeptide chains with 1 heme each capable of binding 1 O2

Question 8

What type of cooperativity does Hb display and why?

Answer 8

Positive cooperativity, receptor occupancy is more receptive to change with positive coop. sigmoid shaped curve, higher affinity as curve moves to the left.

Question 9

What type of cooperativity does Myo. display and why?

Answer 9

Non - cooperative because it is less sensitive to changes to ligand binding. ( less affinity to oxygen)

Question 10

what are primary features of positive cooperativity?

Answer 10

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.

Question 11

T, taut HB state factors:

Answer 11

Low affinity for O2, prevalent at low O2 in tissues

Question 12

R relaxed HB state factors:

Answer 12

higher affinity for O2, prevalent at high O2 in lungs

Question 13

How does the presence of O2 affect T/R confirmation?

Answer 13

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.

Question 14

how does ligand binding affect positive cooperativity?

Answer 14

When ligand is not bound, there is low affinity, when ligand binds to site, becomes high affinity ( must have 2+ binding sites)

Question 15

How does O2 act as an allosteric modifier?

Answer 15

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.

Question 16

How are heterotropic allosteric modifiers different from homotropic?

Answer 16

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.

Question 17

List the heterotropic allosteric modifiers :

Answer 17

bpg 3, co2, ph (H+) all are heterotropic inhibitors

Question 18

How does H+ inhibit the binding of O2 to Hb?

Answer 18

increasing H+ = decreasing pH, DECREASES the amount of O2 bound to Hb. When H+ decreases and pH increases, the R state becomes more stable.

Question 19

what type of bond does Co2 form with the terminal amine group of Hb?

Answer 19

covalent bond that releases H+ and stabilizes the T state

Question 20

How does BPG decrease affinity for O2 in Hb?

Answer 20

BPG stabilizes the t state by binding at a site distant from the O2 binding site.

Question 21

why does HbF have a higher affinity to oxygen than HbA?

Answer 21

HbF does not bind well to BPG( has lower affinity to BPG), has a MUCH higher affinity to oxygen than most common HbA.

Question 22

what is thalassemias

Answer 22

impaired synthesis of alpha or beta chains, complete lack of alpha chains usually fatal

Question 23

sickle cell anemia

Answer 23

glu–> val mutation, HbS forms insoluble fibers, gives proteins sickle cell shape

Question 24

what factors increase affinity for O2?

Answer 24

O2 and CO binding to the active site increase affinity for O2

Question 25

does the first ligand bound have a higher or lower affinity in positive cooperativity?

Answer 25

Lower affinity , t state, higher KD than subsequent ligands bound

Question 26

why is O2 a homotropic allosteric modifier?

Answer 26

It binds to the actual active site of the ligand

Question 27

how does O2 bind to Hb?

Answer 27

02 binds to heme iron through a coordinate bond with the proximal histidine.

Question 28

myoglobin has a _______ affinity to oxygen than Hemoglobin.

Answer 28

HIGHER

Question 29

what biochemical property is unique to the allosteric modulation of Hb?

Answer 29

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.

Question 30

what feature of fetal hemoglobin facilitates delivery of O2 from the maternal HbA to HbF?

Answer 30

HbF has a lower affinity for BPG than HbA. HbF has a higher affinity for oxygen than HbA

Question 31

heterotropic modifiers _______________

Answer 31

lower affinity of Hb to O2

Question 32

large Kd=________ affinity

Answer 32

lower affinity

Question 33

CO stabilizes the ______confirmation

Answer 33

R . binds at active site and has higher affinity to O2, binds very tightly and competes with O2- why it is deadly