protein ligand interactions

Question 1

because oxygen is poorly soluble in aq soln and diffusion is not very effective, what is necessary?

Answer 1

mechanism for O2 transport and storage

Question 2

what does hemoglobin?

Answer 2

transports molecular oxygen from lung to tissue, then transports CO2 from tissue to lung

Question 3

what does myoglobin do?

Answer 3

stores molecular oxygen in tissue; binds O2 reversibly

Question 4

how many AA residues are on a single polypeptide chain?

Answer 4

153

Question 5

what is the structure of myoglobin?

Answer 5

tertiary structure of 8 right-handed a helices with a hydrophobic pocket, which forms a protective sheath for a heme group with iron atom in the middle

Question 6

what structure is typical vs unusual for myoglobin?

Answer 6

secondary structure unusual while tertiary structure is typical of water soluble globular protein

Question 7

what does each heme contain?

Answer 7

one central, coordinately bound, iron atom that is normally in the Fe+2, or ferrous oxidation state

Question 8

what is true about the heme in myoglobin and hemoglobin?

Answer 8

Fe+2 is octahedral coordinated; Fe+2 covalently bonded to the imidazole group of histidine 93; O2 held on other side by histidine 64

Question 9

what is the heme-protein conjugate strongly stabilized by?

Answer 9

hydrophobic interactions between the heme tetrapyrrole ring system and hydrophobic R groups

Question 10

what is the heme-protein conjugate stabilized further by?

Answer 10

coordination of the iron atom with the nitrogen atom of the histidine R-group

Question 11

what is responsible for the asphyxiation in carbon monoxide poisoning?

Answer 11

the preferential binding of carbon monoxide to heme iron

Question 12

what protects Fe+2 from irreversible oxidation to Fe+3?

Answer 12

the heme and protein

Question 13

how are O2 and CO different in their binding?

Answer 13

O2 binds to free heme at an angle (weakening the binding) while CO2 binds to free heme perpendicular to the heme plane

Question 14

what is true about each chain of hemoglobin?

Answer 14

each one has a heme group meaning four O2 can bind to each Hb

Question 15

what is hemoglobin responsible for?

Answer 15

binding oxygen in the lung and transporting, in the blood vessels, the bound oxygen throughout the body, where it is used in aerobic metabolic pathways

Question 16

what affects hemoglobin’s oxygen carrying properties?

Answer 16

the variations in AA composition that exist

Question 17

the quaternary structure of hemoglobin leads to…

Answer 17

physiologically important allosteric interactions between the subunits

Question 18

what is true about myoglobin and hemoglobin?

Answer 18

although they have differing sequences, the structures are practically the same

Question 19

allosteric protein

Answer 19

protein in which the binding of a ligand at one binding site affects the binding properties of another site in the same protein

Question 20

_______ is the result of Hb’s quaternary structure, and the reason that Hb is more sensitive to changes in O2 than Mb

Answer 20

allosteric effect

Question 21

monomeric Mb has a single _____________.

Answer 21

O2 binding affinity

Question 22

what contributes to changes in the conformation of the quaternary structure?

Answer 22

conformational changes at the subunit surface change binding interactions with adjacent subunits

Question 23

what causes the a-b subunit pairs to slide past each other?

Answer 23

when O2 binds, there is a large change in the a1-b2 (& a2-b1) contact

Question 24

what is known as the tense state?

Answer 24

tertiary configuration of low affinity, deoxygenated hemoglobin

Question 25

what is known as the relaxed state?

Answer 25

quaternary structure of fully oxygenated high affinity form of hemoglobin

Question 26

what is true about the curves for oxygen binding to myoglobin and hemoglobin?

Answer 26

linear for myoglobin binding, but curve for hemoglobin has 3 phases, which is typical of allosteric proteins in which the substrate is a positive homotropic effector

Question 27

sickle cell anemia

Answer 27

singe AA residue on the surface of the b chain, at the 6th position along the B chain, is mutated from Glutamate-6 to Valine-6 (creates sticky hydrophobic contact point of outside of b chain)