focus chapter 9 (hemoglobin and allosterism)

Question 1

myoglobin localization

Answer 1

In the cytosol of muscle cells

Question 2

myoglobin structure

Answer 2

• Single polypeptide
• All alpha-helical
• One heme per molecule, thus can only bind one oxygen molecule

Question 3

myoglobin function

Answer 3

• Binding and storage of oxygen in muscle
• Facilitates oxygen transport in muscle
• Found in red muscle tissue

Question 4

hemoglobin functions

Answer 4

• Transports oxygen from the lungs to the peripheral tissues
• Transports carbon dioxide from the peripheral tissues to the lungs
• Transport oxygen, H+, and CO2

Question 5

hemoglobin localization

Answer 5

In red blood cells(plasma protein)

Question 6

hemoglobin structure

Answer 6

• Multi-subunit protein
• All alpha helical
• 1 heme/subunit- 1 oxygen/subunit
  4 subunits

Question 7

Describe the structure of the heme groups in hemoglobin, and how it changes between the O2 bound and unbound states

Answer 7

o Consists of an organic component called protoporphyrin and a central iron ion in the ferrous (Fe2+) form.
o The iron lies in the middle of the protoporphyrin bound to four nitrogens.
o Iron can form two additional bonds, called the fifth and sixth coordination sites.
o The fifth coordination site is occupied by an imidazole ring of a histidine called the proximal histidine.
o The sixth coordination site binds oxygen. Upon oxygen binding, the iron moves into the plane of the protoporphyrin ring.

Question 8

Deoxyhemoglobin

Answer 8

 T state of allosteric enzymes
* Tense
 Low affinity for oxygen

Question 9

Oxyhemoglobin

Answer 9

 R state of allosteric enzymes
* High affinity for oxygen

Question 10

The transition from T state to R state occurs upon

Answer 10

oxygen binding

Question 11

The transition from T state to R state

Answer 11

o The iron ion moves into the plane of the heme when oxygen binds. The proximal histidine, which is a component of an alpha helix, moves with the iron
o The resulting structural change is communicated to the other subunits (rotation)

Question 12

Oxygen binding is measured as a function of the

Answer 12

partial pressure of oxygen (pO2)

Question 13

Sigmoidal shape indicates cooperativity, due to

Answer 13

interactions between distinct O2 binding sites

Question 14

Explain how effector molecule 2,3-BPG regulates the physiological process of O2 transport, especially the binding and release of O2 by hemoglobin

Answer 14

 Binding at the interface of all four subunits
 Contact with the Beta subunits
 Stabilization of T state and oxygen dissociation

Question 15

Explain how effector molecules CO2 and H+ regulate the physiological process of O2 transport, especially the binding and release of O2 by hemoglobin

Answer 15

 Enhance oxygen release by hemoglobin
 Bohr effect

Question 16

Describe the biochemical and genetic defects associated with Sickle Cell Disease.

Answer 16

o Sickle shaped red blood cells are fragile and less flexible than normal RBCs resulting in anemia, blocking capillaries, and damaging tissues
o Sickle cell trait protects heterozygotes against malaria
o In the Beta globin gene: point mutation adenine to uracil
o In the beta globin protein: Glu residue changed to Val at position 6
o AA at position 6 localized on the surface of the b-globin protein.
o The valine binds in a hydrophobic pocket found in a b-globin subunit on another hemoglobin molecule. This pocket is exposed when oxygen is released in tissue capillaries.
o This process progresses to include additional hemoglobin molecules, which stack into long filamentous polymers. Mutated hemoglobins precipitate out of solution and deform the shape of red blood cells (sickling of cells).