Proteins: Myoglobin And Hemoglobin

Question 1

What is the orientation of hydrophobic and hydrophilic amino acids in globular proteins?

Answer 1

Hydrophobic amino acids are oriented towards the center

Hydrophilic are on the outside

Question 2

Name 5 functions of globular proteins

Answer 2

Storage
Transport
Defense
Muscle Contraction
Catalysts

Question 3

Why is a heme prosthetic group used to bind and carry oxygen?

Answer 3

Protein side chains lack an affinity for oxygen and free transition metals generate free radicals

Question 4

What is the structure and function of Myoglobin?

Answer 4

A single polypeptide chain with a covalently bound heme group.

Used to store oxygen, binds well at very low concentration

Question 5

What is the structure and function of hemoglobin?

Answer 5

Hemoglobin is a tetramer of two alpha and two beta subunits with each polypeptide chain containing a heme group

Hb transports oxygen throughout the body

Question 6

What is the structure of a Heme prosthetic group?

Answer 6

A porphyrin ring that is flat and open on two sites, containing an iron atom in the center

Question 7

What is the role of the amino acids that create the pocket for oxygen binding?

Answer 7

These hydrophobic amino acids protect the heme from binding other molecules.

Question 8

What are the properties of the T state of Hemoglobin?

Answer 8

More interactions, more stable
Lower affinity for oxygen
Stabilized by 2.3-BPG

Question 9

What are the properties of the R state of Hemoglobin?

Answer 9

Fewer interactions, more flexible

High affinity for oxygen

Question 10

What is cooperatively and how is it related to Hemoglobin?

Answer 10

A binding event affects the affinity of binding at the other sites.

The first oxygen-binding event ruptures the salt bridges associated with the T state, favoring the R state and making it easier for more oxygen to bind

Question 11

What is the Bohr effect?

Answer 11

The reciprocal binding of protons and oxygen to hemoglobin.

Tissues - H+ binds, O2 released

Lungs - H+released, O2 binds

Question 12

How does the lower pH of the tissues stabilize the T state of Hemoglobin?

Answer 12

Protonation of His146 which then forms a salt bridge with Asp94

Question 13

What is the role of 2,3-Bisphosphoglycerate and how does it accomplish this?

Answer 13

2,3-BPG stabilizes the T state by stabilizing the positive charges of side changes in the beta subunits.

Question 14

What is the role of the distal histidine?

Answer 14

The distal histidine forces CO to bind at an angle, which reduces its affinity to bind to the heme group.

Question 15

What are the alpha-globin-like genes and where are they located?

Answer 15

Zeta
A1
A2

Located on Chr. 16

Question 16

What are the beta-globin like genes and where are they located?

Answer 16

E
Gy
Ay
B
 Sigma

Located on Chr. 11

Question 17

What is the globin combination for a normal adult?

Answer 17

A2B2

Question 18

What is the Globin combination for a person with sickle cell?

Answer 18

A2Bs2

Question 19

What is the globin combination for an infant?

Answer 19

A2y2

Question 20

Why does HbF have a higher affinity for oxygen than HbA?

Answer 20

So that the fetal blood can receive sufficient oxygen from the mother.

Question 21

What mutation causes Sickle Cell Anemia?

Answer 21

Single nucleotide change in the B-globin gene that changes Glu to Val at position 6

Question 22

What is the cause of Hemoglobin C? And what is the result?

Answer 22

Conversion of Glu6 to Lys6 in the B-globin gene

Causes mild hemolytic anemia

When combined with sickle cell, can be serious.

Question 23

What is Methemoglobinemia and what is its cause?

Answer 23

Hb contains Fe3+ instead of Fe2+, which results in a reduced ability to bind oxygen.

Cause by a deficiency in NADH-methemoglobin reductase.

Causes cyanosis