Chapter 9 (Exam 2) Flashcards
What are globins?
Oxygen-binding proteins.
What is myoglobin?
Muscle protein.
Heme-containing monomeric protein.
Major function is to store O2.
What is hemoglobin?
Major protein of red blood cells.
Heme-containing tetramer (4 polypeptide chains; 2a + 2b).
Major function is to carry O2 from lungs to tissues.
What does the heme group consist of?
An organic component called protoporphyrin and a central iron ion in the ferrous (Fe2+) form.
Where is the iron located in the heme structure?
In the middle of the protoporphyrin.
Has 6 coordination bonds: 4 in the plane of porphyrin ring bound to nitrogens and 2 perpendicular to it (5th and 6th coordination sites).
What is the 5th coordination site occupied by?
Proximal histidine: imidazole ring of a histidine.
What does the 6th coordination site bound to?
Oxygen.
What happens upon oxygen binding?
Iron moves into the plane of the protoporphyrin ring.
How does oxygen binding change the position of the iron ion?
The iron ion lies slightly outside the plane of the porphyrin in deoxyhemoglobin heme but moves into the plane of the heme on oxygenation.
What is hemoglobin?
A tetramer of 2 identical dimers (a2b2).
What must vary for effective transport?
Affinity with pO2.
How can affinity to oxygen change?
It must be a protein with multiple binding sites.
Binding sites must be able to interact with each other.
The phenomenon is called cooperativity.
What is cooperativity?
Positive cooperativity:
- First binding event increases affinity at remaining sites.
- Recognized by sigmoidal binding curves.
Negative cooperativity:
- First binding event reduces affinity at remaining sites.
What affinity to O2 does Hemoglobin have at R and T states?
T state: lower affinity to O2.
R state: higher affinity to O2.
What is the T state of Hemoglobin?
Tense state.
More interactions, more stable.
Lower affinity for O2.
