Protein Function: Oxygen Binding proteins Flashcards
What do many protein functions involve?
the reversible binding of ligands (partner molecules).
What is the function of ligands?
bind to specific locations called binding sites whose 3D structure and properties complement those of the ligand (size, shape, hydrophobicity, charge etc.)
How could the ligand interactions be described?
specific–> the protein can discriminate between thousands of different molecules it encounters
What may ligand binding also involve?
conformational change –> induced fit
02 is a _____ molecule and poorly soluble in _______ solution
non polar, aqueous
Diffusion of 02 into tissues is ______
inefficient
What is Myoglobin?
a simple 02 binding protein of mammalian muscle tissues
How is oxygen transported around the body?
via Haemoglobin
Describe the Quaternary structure of Haemoglobin
-A tetramer with a a2B2 structure
-a-subunit contains 141 amino acids
-B subunit contains 146 amino acids
What does Oxygen binding lead to? What binding behaviour could it be described as?
conformational changes–> allosteric behaviour
What does the change in structure do?
the affinity of the molecule for it’s ligand
What does this binding break?
a salt bridge
What are the 2 states of tetramers?
-Low affinity state
-High affinity state
How could the binding curve be described as?
sigmoidal
How could the curve also be described? Why?
a hybrid curve reflecting the transition from a low-affinity to a high-affinity state
What does co-operative binding render haemoglobin as?
more sensitive to the small changes in P02 between the tissues and the lungs
What does this allow?
this allows haemoglobin to bind to oxygen in the lungs (high PO2) and release it in the tissues (low PO2).
What does Myoglobin bind to?
O2 readily but becomes saturated at a low PO2
Haemoglobin is_____ to take up O2 at first; its affinity____ with O2 uptake
reluctant, increases
In the lungs, both proteins would be____ with O2
saturated
Carbon dioxide does not bind in the place of_____
oxygen
What binds at an extremely high affinity in the place of oxygen?
carbon monoxide
Describe the Bohr curve
-Low PH shifts the 02 binding curve
-In muscle high (H+) and CO decrease the affinity of Hb for O2
-In lungs high (O2) drives off bound H+
What is 02 binding regulated by?
2,3 bisphosphoglycerate
Describe foetal haemoglobin
higher affinity for oxygen so that oxygen can diffuse from mother to child
What does the term “allosteric effects” refer to in proteins?
Changes in protein structure that affect ligand affinity, often seen in multi-subunit proteins
How does oxygen binding affect haemoglobin’s structure?
Oxygen binding induces conformational changes that stabilise the R-state (high affinity).
What is the significance of the dissociation constant (Kd)?
Kd reflects the affinity between a protein and its ligand; lower Kd indicates higher affinity.
Why is fetal haemoglobin important?
It allows for efficient oxygen transfer from the mother, as fetal lungs are not used for breathing.
What is the most common single gene disorder in Black Americans?
Sickle cell anemia, occurring in approximately 1 in 375 individuals.
