Lecture 9 - Protein Ligand Interactions

Question 0

What does myoglobin do?

Answer 0

Stores molecular oxygen in tissue

Question 1

Hemoglobin transports molecular oxygen from ________ to _________, then transports CO2 from ________ to _________.

Answer 1

Lung to tissue

Tissue to lung

Question 2

How many hemoglobin monomers are there?

Answer 2

4: α1, α2, β1, β2

Question 3

Where is a heme group bound in each polypeptide chain?

Answer 3

Between helix E and F

Question 4

How many amino acid residues are there in a single polypeptide chain of myoglobin?

Answer 4

153

Question 5

Describe the structure of myoglobin

Answer 5

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

Question 6

In terms of myoglobin properties, what happens during periods of oxygen depletion?

Answer 6

Oxy-myoglobin releases its bound oxygen which is then used in metabolism

Question 7

True or false? Secondary structure of myoglobin is unusual

Answer 7

True

Question 8

True or false? Secondary structure of myoglobin is typical of water soluble globular protein.

Answer 8

False, TERTIARY not secondary

Question 9

The oxygen carried by heme-proteins (both myoglobin and hemoglobin) is bound directly to what??

Answer 9

To the ferrous iron atom of the heme prosthetic group

Question 10

True or false? Fe2+ is tetrahedral coordinated in myoglobin and hemoglobin

Answer 10

FALSE, OCTAHEDRAL not tetrahedral

Question 11

CO binds to free heme how many times better than O2? And how many times better than O2 to hemoglobin?

Answer 11

20,000 times

250 times

Question 12

What is he difference between the binding of O2 and CO to a free heme?

Answer 12

O2 binds to free heme at an angle whereas CO binds to free heme perpendicular to heme plane

Question 13

Describe the structure of hemoglobin

Answer 13

Tetramer of four polypeptide chains
Two identical α chains (141 AA residues) and two identical β chains (146 AA residues)
Each chain has a heme group, hence four O2 can bind to each Hb

Question 14

How many identical AA residues do the three polypeptide chains of Mb, α-Hb, and β-Hb have?

Answer 14

27

Question 15

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

Answer 15

Allosteric protein

Question 16

True or false? When the first O2 molecule binds to the first subunit of completely deoxygenated hemoglobin, this binding decreases the affinity of the remaining hemoglobin subunits for O2.

Answer 16

FALSE, it INCREASES the affinity

Question 17

True or false? As additional O2 is bound to the second and third subunits of hemoglobin, O2 binding is further strengthened, incrementally

Answer 17

TRUE

Question 18

Monomeric myoglobin has how many O2 binding affinity?

Answer 18

Only ONE

Question 19

The α1-β1 (and α2-β2) interface involves more than ____ residues, but the α1-β2 (and α2-β1) involve only ____ residues

Answer 19

30

19

Question 20

What is the tense (T) state?

Answer 20

The tertiary configuration of low affinity, deoxygenated hemoglobin

Question 21

What is the relaxed (R) state?

Answer 21

The quaternary structure of the fully oxygenated high affinity form of hemoglobin

Question 22

What is the difference between the curve of oxygen binding to myoglobin versus the oxygen binding to hemoglobin?

Answer 22

O2 binding to myoglobin is linear

O2 binding to hemoglobin has 3 phases: hemoglobin, Hb high affinity state, and Hb low affinity state

Question 23

Where does the CO2 bind to deoxy-Hb?

Answer 23

At the amino-terminal end of each globin chain

Question 24

Deoxy-Hb carries CO2 to the _______ and H+ to the _________

Answer 24

Lungs

Kidneys

Question 25

What converts CO2 to HCO3- ?

Answer 25

Carbonic anhydrase

Question 26

What is the sea level BPG?

Answer 26

5 mM

Question 27

What is the BPG at high altitudes?

Answer 27

8 mM

Question 28

True or false? In sickle cell anemia, a single amino acid residue on the surface of the β chain at position 6 is mutated

Answer 28

True, mutated from Glu-6 to Val-6

Question 29

True or false? In sickle cell anemia, position 6 mutation creates a “sticky” hydrophobic contact point on the outside of the β chain

Answer 29

True

Question 30

An immune system anti-body protein in blood serum

Answer 30

Immunoglobin G (IgG)

Question 31

How many antigen binding sites (Fab) does immunoglobin G have?

Answer 31

2

Question 32

The binding specificity of the antibody is determined by what?

Answer 32

The AA’s in the variable domains of the light and heavy polypeptide chains