Oxygen Binding

Question 1

What is the problem with oxygen in regards to the protein side chains?

Answer 1

Animals need to have O2 but protein side chains are unable to bind O2

Question 2

Why aren’t transition metals used for oxygen bindings in animals?

Answer 2

Although they are able to bind O2, they would cause damage if free in solution

Question 3

Why isn’t organometallic compounds such as heme used for oxygen binding in animals?

Answer 3

Heme contains Fe2+, and when free, would be oxidized to Fe3+

Question 4

How is Heme used in oxygen binding?

Answer 4

Heme, bound to a protein, captures oxygen molecules

Question 5

What is the function of Myoglobin in oxygen binding?

Answer 5

Myoglobin is a protein that is used to store oxygen. It is often found in muscles

Question 6

What is the function of Hemoglobin in oxygen binding?

Answer 6

Hemoglobin transports oxygen. It is a heterotetramer

Question 7

When do you express concentrations in terms of partial pressure?

Answer 7

When the molecule that is bound is a gas

Question 8

What is P50?

Answer 8

P50 is measured in kPa and is the oxygen concentration in which the fractional saturation is 50 (measured like Kd in terms of a graph)

Question 9

How would you find the partial pressure of oxygen if given the fractional saturation?

Answer 9

fractional saturation = pO2 / (pO2+P50)

Question 10

What is the relation between myoglobin and carbon monoxide?

Answer 10

CO and O2 are similar in size and shape and therefore are able to fit in the same binding site. CO binds better than O2 because carbon has a filled lone electron pair which can be donated to vacant orbitals on the Fe2+.

Question 11

Why is carbon monoxide highly toxic?

Answer 11

Carbon monoxide competes with oxygen. Carbon monoxide blocks the function of myoglobin, hemoglobin, and mitochondrial cytochromes involved in oxidative phosphorylation

Question 12

Why do we have two different proteins to store and transport oxygen?

Answer 12

Affinity changes with pressure changes.

Question 13

Does hemoglobin have a higher affinity for the partial pressure in the tissue or the lungs?

Answer 13

The lungs

Question 14

Explain allostery and hemoglobin

Answer 14

Hemoglobin needs an affinity in higher pressure in the lungs and and lowered affinity in the lower pressure in the tissues. To be able to do this, the protein must have multiple binding sites. The interactions between these binding sites is allostery.

Question 15

What is positive cooperativity?

Answer 15

It is positive allostery. The first binding event increases affinity at the remaining binding sites and is recognized by sigmoidal curves.

Question 16

What is negative cooperativity?

Answer 16

It is negative allostery. The first binding reduces affinity at remaining binding sites.

Question 17

What type of cooperativity does hemoglobin have?

Answer 17

positive.

Question 18

With the first binding event of hemoglobin, do the remaining bind sites have an increased or decreased affinity?

Answer 18

Increased because it is positive cooperativity

Question 19

What can be said of hemoglobin because of the sigmoid binding curve?

Answer 19

hemoglobin is more sensitive to small differences in O2 concentration between tissues and lungs allowing it to bind oxygen in the lungs (with higher pressure) and release oxygen in the tissues (with the lower pressures).

Question 20

What does myoglobin’s Kd say about its relation to O2?

Answer 20

Myoglobin’s Kd makes it great at storing O2 at normal tissue O2 levels

Question 21

What is the T-state of hemoglobin?

Answer 21

The tense or tight state. This is the most stable state and has a lowered affinity for O2

Question 22

What is the R-state of hemoglobin?

Answer 22

The relaxed state. This is the most flexible state and has a higher affinity for O2.

Question 23

What state of hemoglobin has the higher affinity for O2?

Answer 23

R-state

Question 24

What state of hemoglobin is the most stable?

Answer 24

T-state

Question 25

What state of hemoglobin is the most flexible?

Answer 25

R-state

Question 26

What state of hemoglobin has the lowered affinity for O2?

Answer 26

T-state

Question 27

How does BPG regulate hemoglobin?

Answer 27

BPG is form of allosteric regulation. 2,3-BPG binds hemoglobin which stabilizes the T-structure where O2 binding is not preferred

Question 28

What state of hemoglobin is related to BPG?

Answer 28

T-state

Question 29

How does 2,3-BPG binding affect O2 affinity?

Answer 29

It lowers the affinity for O2 binding. The binding of 2,3-BPG allows O2 release in tissues and adaption to changes in altitude.

Question 30

What effect would increased blood BPG have on P50 for hemoglobin?

Answer 30

It would decrease the P50

Question 31

What would occur if there was no 2,3-BPG?

Answer 31

Hemoglobin would have a binding profile that resembles an exponential curve

Question 32

What is responsible for the color of blood?

Answer 32

The heme group is a strong chromophore which absorbs light

Question 33

Why is it important that iron is incorporated into the heme group, rather than the free in the cell?

Answer 33

If heme was free, the iron would be oxidized to the 3+ state.

Question 34

How is the heme group attached to the myoglobin?

Answer 34

The heme is in the hydrophobic cleft, the heme group is stabilized by hydrophobic interactions

Question 35

Do the lungs or the tissues have a higher partial pressure?

Answer 35

The lungs