Chapter 3 Flashcards
What is a receptor-ligand interaction?
A receptor (R) binds to a ligand (L) to form a complex (RL), which can be reversible and is influenced by concentration.
What does L₁/₂ represent?
The concentration of ligand at which half of the receptors are bound.
What does the estrogen receptor bind?
Estradiol, a steroid hormone that regulates female reproductive development.
Why can the estrogen receptor bind estradiol but not testosterone?
The binding pocket is lined with hydrophobic residues and is shaped to fit estradiol. Testosterone would sterically clash due to its different structure.
What is the function of myoglobin?
It binds and stores oxygen in muscle tissues for use when needed.
How does oxygen binding affect myoglobin’s iron atom?
Oxygen binding moves iron (Fe²⁺) into the plane of the heme ring, converting deoxymyoglobin → oxymyoglobin.
What is the shape of myoglobin’s oxygen-binding curve?
Hyperbolic (non-cooperative binding).
Why are superoxides (O₂⁻) dangerous?
They are reactive and can damage biological molecules.
How does myoglobin prevent superoxide release?
A distal histidine stabilizes bound oxygen, ensuring that O₂ is released as dioxygen (O₂) rather than O₂⁻.
How does CO compete with O₂ for binding to myoglobin?
CO binds to the heme iron much more tightly than O₂, reducing oxygen transport efficiency.
How is hemoglobin different from myoglobin?
Hemoglobin: Found in blood, transports oxygen.
Myoglobin: Found in muscles, stores oxygen.
What is the structure of hemoglobin?
Four subunits (2 α + 2 β chains), each with a heme group.
What is cooperative oxygen binding in hemoglobin?
The binding of oxygen to one subunit increases the oxygen affinity of the remaining subunits.
What does the sigmoidal binding curve indicate?
Cooperativity: Hemoglobin binds oxygen efficiently in the lungs and releases it in tissues.
How does exercise influence oxygen release from hemoglobin?
Increased CO₂, H⁺ (lower pH), and temperature enhance oxygen release (Bohr effect).
What are the two models for hemoglobin cooperativity?
Concerted Model: Hemoglobin exists only in T-state (low affinity) or R-state (high affinity).
Sequential Model: Oxygen binding gradually increases the affinity of remaining subunits.
Which model explains hemoglobin behavior better?
A mix of both: Hemoglobin mainly follows the concerted model, but shows some sequential characteristics.
What happens structurally when hemoglobin binds oxygen?
Oxygen binding moves iron (Fe²⁺) and shifts histidine, triggering a 15° rotation between subunits, converting T-state → R-state.
How does 2,3-BPG influence oxygen binding?
Stabilizes T-state, decreasing oxygen affinity.
Increases oxygen release in tissues.
Fetal hemoglobin has a lower affinity for 2,3-BPG, allowing greater oxygen uptake from maternal blood.
How do pH and CO₂ influence hemoglobin function?
Lower pH (higher H⁺) stabilizes T-state, increasing oxygen release.
CO₂ forms carbamates, further stabilizing T-state.
Why is CO poisoning dangerous?
CO binds hemoglobin with 200× greater affinity than O₂.
Prevents oxygen delivery to tissues.
What is a treatment for CO poisoning?
High oxygen concentration to displace CO from hemoglobin.
What causes sickle cell anemia?
A mutation in β-globin (Glutamate → Valine at position 6).
Why does this mutation cause sickling?
Valine is hydrophobic, leading to hemoglobin aggregation.
Causes distorted, rigid red blood cells that block capillaries.
