32 Questions
What is the shape of the binding curve of hemoglobin for oxygen?
Sigmoid
What is the effect of the first molecule of O2 binding to deoxyhemoglobin?
It leads to a conformational change that makes it easier for additional O2 molecules to bind
What is the term for a protein in which the binding of a ligand to one site affects the binding properties of another site on the same protein?
Allosteric protein
What is the role of carbonic anhydrase in the transport of CO2 by hemoglobin?
It catalyzes the hydration of CO2 to form bicarbonate
What is the term for the effect of pH and CO2 concentration on the binding and release of oxygen by hemoglobin?
Bohr Effect
What is the role of 2,3-bisphosphoglycerate (BPG) in the regulation of oxygen binding to hemoglobin?
It decreases the affinity of hemoglobin for oxygen
What is the term for the interaction between oxygen and hemoglobin, where oxygen acts as both a ligand and a modulator?
Homotropic interaction
What is the consequence of inadequate functioning of the lungs or circulatory system on oxygenation of peripheral tissues?
Decreased oxygenation of peripheral tissues due to hypoxia
What is the term for the site on a protein to which a ligand binds?
Binding site
What is the result of the binding of a protein and ligand?
A conformational change in the protein that makes the binding site more complementary to the ligand
What is the role of the coordinated nitrogen atoms in the heme group?
To help prevent conversion of the heme iron to the ferric (Fe3+) state
Why is oxygen poorly soluble in aqueous solutions?
The reason is not specified in the content
What is the function of hemoglobin and myoglobin?
To maintain a supply of oxygen essential for oxidative metabolism
What happens to the heme iron when O2 occupies the 6th coordination position?
It moves towards the plane of the heme
What is the significance of the 3-dimensional structure of myoglobin determined by John Kendrew?
It was the first protein to have its structure determined
What is the prosthetic group common to myoglobin and hemoglobin?
Heme
What is the central atom in the planar tetrapyrole of heme?
Fe2+
What is the function of myoglobin in red muscle?
To store oxygen as a reserve against oxygen deprivation
What is the shape of the oxygen binding curve of myoglobin?
Hyperbolic
What is the coordination number of the iron atom in heme?
6
What is the effect of free iron on macromolecules?
It leads to the formation of highly reactive oxygen species that can damage them
What is the quaternary structure of hemoglobin?
A tetramer
What is the shape of the oxygen binding curve of hemoglobin?
Sigmoid
What is the function of hemoglobin in the body?
To transport oxygen to the tissues and return CO2 and protons to the lungs and kidneys
Why is myoglobin less effective for oxygen transport compared to hemoglobin?
It is less sensitive to small changes in ligand concentration
What is the primary reason why CO is highly toxic to aerobic organisms?
It binds to heme iron with a higher affinity than O2
What is the result of oxygen binding to hemoglobin in the R state?
Stabilization of the R state
What is the primary difference between the T and R states of hemoglobin?
The structural conformation of the subunits
What is the result of the transition from the T state to the R state of hemoglobin?
A shift to a higher affinity state
What is the advantage of hemoglobin's cooperative binding of oxygen?
It allows for a transition between high and low affinity states
What would be the result of a protein that binds oxygen with high affinity?
It would bind oxygen efficiently in the lungs but not release it in the tissues
What is the primary function of myoglobin in exercise tissues?
Oxygen storage
Study Notes
Ligand Binding
- A ligand is a molecule bound reversibly by a protein
- Binding site is the site on a protein to which a ligand binds, complementary to the ligand in size, shape, charge, and hydrophobic or hydrophilic character
- Induced fit: the structural adaptation that occurs between a protein and ligand, making the binding site more complementary to the ligand, permitting tighter binding
Oxygen-Binding Proteins
- Hemoglobin and myoglobin are heme proteins that maintain a supply of oxygen essential for oxidative metabolism
- Myoglobin (Mb) and beta subunits of hemoglobin (Hb) share almost identical secondary and tertiary structures
Heme
- Heme is the prosthetic group common to myoglobin and hemoglobin
- Heme consists of a cyclic tetrapyrole (protoporphyrin) with a single iron atom in its ferrous (Fe2+) state
- The iron atom has six coordination bonds: four to nitrogen atoms of the flat porphyrin ring system and two perpendicular to the porphyrin
- Iron in the Fe2+ state binds oxygen reversibly; in the Fe3+ state, it does not bind oxygen
Oxygen Binding
- When O2 occupies the 6th coordination position, a conformational change occurs:
- The heme iron moves towards the plane of the heme from a position of 0.04 nm beyond it
- The bond between the first O2 and Fe2+ is perpendicular to the plane of the heme ring
Myoglobin
- Myoglobin is a monomeric protein of red muscle
- Stores oxygen as a reserve against oxygen deprivation and facilitates oxygen diffusion rapidly in contracting muscle for mitochondrial synthesis of ATP
- Single polypeptide chain of 153 AA residues with one heme molecule
- Compact, dense, hydrophobic core
- Oxygen binding curve is hyperbolic, relatively insensitive to small changes in the concentration of dissolved O2
Hemoglobin (Hb)
- Tetrameric protein (quaternary structure) consisting of four polypeptide chains (2 alpha, 2 beta) and 4 heme prosthetic groups
- Transports O2 to the tissues and returns CO2 and protons from peripheral tissues to lungs and kidneys for excretion
- Hemoglobin structure: protein portion is globin with 2 alpha chains (141 residues each) and 2 beta chains (148 residues each)
- More sensitive to small differences in O2 concentration between tissues and lungs
- Hb has a sigmoid binding curve for O2 due to cooperative binding
Cooperativity of Hb-O2 Binding
- Hb undergoes a structural change on binding oxygen, with two major conformations: the R state and the T state
- Oxygen binding stabilizes the R state
- A transition from the low-affinity T state to the high-affinity R state occurs as more O2 molecules are bound
- Hb has a hybrid S-shaped or sigmoid binding curve for oxygen due to cooperativity
- Cooperativity: the binding of one O2 molecule affects the binding of subsequent O2 molecules
Regulation of Hemoglobin
- Salt bridges between the carboxyl terminal residues of all 4 subunits rupture progressively as oxygen is added, leading to the transition from the T state to the R state
- Hb also transports H+ and CO2 as end products of cellular respiration
- 2,3-Bisphosphoglycerate (BPG) reduces the affinity of Hb to O2 by stabilizing the T state
- Bohr Effect: the effect of pH and CO2 concentration on the binding and release of oxygen by hemoglobin
Learn about the binding of ligands to proteins, including hemoglobin and myoglobin. Understand the importance of binding sites and conformational changes in protein-ligand interactions.
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