Structure-Function of Myoglobin and Hemoglobin

Myoglobin is responsible for storing oxygen in muscles.

Hemoglobin is responsible for transporting oxygen and carbon dioxide throughout the body. It also helps in blood buffering.

Both myoglobin and hemoglobin are hemoproteins.

<p>The function of the heme (D)</p> Signup and view all the answers

<p>Myoglobin is a monomeric protein.</p> Signup and view all the answers

<p>Myoglobin is mainly found in muscle tissue.</p> Signup and view all the answers

<p>Myoglobin can exist as oxymyoglobin (oxygen-bound) and deoxymyoglobin (oxygen-free).</p> Signup and view all the answers

<p>The tertiary structure of myoglobin consists of 8 alpha-helices, designated A through H, connected by short non-helical regions.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>True (A)</p> Signup and view all the answers

<p>The two histidine residues in helices E and F are called E7 and F8, respectively.</p> Signup and view all the answers

<p>F8 His is designated as proximal His.</p> Signup and view all the answers

<p>A prosthetic group is a non-protein group that is covalently attached to a protein.</p> Signup and view all the answers

<p>True (A)</p> Signup and view all the answers

<p>The four cyclic groups in heme are called pyrrole rings.</p> Signup and view all the answers

<p>Iron can bind in the center of the four pyrrole rings.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>Iron can form six bonds.</p> Signup and view all the answers

<p>The hydrophobic interior of myoglobin prevents oxidation of iron.</p> Signup and view all the answers

<p>True (A)</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>The chains of hemoglobin interact with each other mainly through hydrophobic interactions.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>The P50 value for myoglobin is approximately 2.8 torr.</p> Signup and view all the answers

<p>The saturation curve of hemoglobin binding to oxygen has a sigmoidal shape.</p> Signup and view all the answers

<p>The R-state of hemoglobin is known as the relaxed state.</p> Signup and view all the answers

<p>Binding of oxygen to hemoglobin causes a conformational change, shifting it from the low-affinity T-state to the high-affinity R-state.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>The sigmoidal shape of the hemoglobin saturation curve is a result of cooperative binding, which ensures efficient delivery of oxygen to tissues.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

The relationship between the structure of a molecule and its function. For example, how the shape of an enzyme allows it to bind to a specific substrate.

Proteins with a compact, spherical shape. They are usually soluble in water and have a diverse range of functions.

A protein found in muscle tissue that stores oxygen for use during periods of high energy demand.

A protein found in red blood cells that transports oxygen from the lungs to the body's tissues and also helps transport carbon dioxide back to the lungs.

Myoglobin and hemoglobin are both examples of hemoproteins. Hemoproteins contain a heme group, a non-protein molecule tightly bound to the protein.

A prosthetic group is a non-protein molecule that is tightly bound to a protein and is essential for its function. Think of it as a sidekick to the protein.

The heme group is a flat molecule with a central iron atom. It's the part of hemoglobin and myoglobin that binds oxygen.

Myoglobin is a single protein chain, also known as a monomer.

Myoglobin exists in two forms: oxymyoglobin, which is bound to oxygen, and deoxymyoglobin, which is not bound to oxygen.

The tertiary structure of myoglobin is a compact, folded chain of amino acids with eight alpha-helices.

Amino acids on the surface of a globular protein are typically hydrophilic, meaning they are attracted to water. This allows the protein to dissolve in water.

Amino acids in the interior of a globular protein are typically hydrophobic, meaning they repel water. This helps the protein maintain its compact shape.

Two histidine residues in myoglobin, designated as E7 and F8, play important roles in oxygen binding.

The F8 histidine residue in myoglobin is called the 'proximal histidine' because it is directly attached to the iron atom in the heme group.

The E7 histidine residue in myoglobin is called the 'distal histidine' because it is located on the opposite side of the heme group from the proximal histidine.

Both myoglobin and hemoglobin contain a heme group, which is a flat molecule with four nitrogen-containing rings arranged in a ring structure.

The iron atom in the heme group can form six bonds: four to the nitrogen atoms in the rings, one to the proximal histidine, and one to oxygen.

When iron is in the ferrous state (Fe2+), it can bind oxygen. However, when it is oxidized to the ferric state (Fe3+), it can't bind oxygen.

The heme group fits snugly into a hydrophobic pocket in the protein, creating a stable interaction. This hydrophobic pocket helps prevent oxidation of the iron atom.

The distal histidine acts like a gate, controlling the entry and exit of oxygen to the heme binding site. It prevents the binding of other molecules, such as carbon monoxide, that could interfere with oxygen transport.

Myoglobin binds oxygen with high affinity, meaning it holds onto oxygen tightly. This is essential for its role in oxygen storage.

P50 is the partial pressure of oxygen required for 50% of the protein molecules to be saturated with oxygen.

Hemoglobin is a tetrameric protein, meaning it is made up of four protein chains.

Hemoglobin is made up of two alpha chains and two beta chains.

The individual chains in hemoglobin interact with each other through hydrophobic interactions, creating a stable structure.

Hemoglobin must bind oxygen efficiently in the lungs, become saturated with oxygen, and then efficiently release oxygen in the tissues where oxygen pressure is lower.

The saturation curve for hemoglobin is sigmoidal, meaning it has an S-shape. This shape reflects the cooperative binding of oxygen to hemoglobin.

Hemoglobin is an allosteric protein, meaning that binding of one molecule to one part of the protein affects binding of another molecule to a different part of the protein.

Hemoglobin exists in two states: the T-state (tense) and the R-state (relaxed). The T-state has low oxygen affinity, while the R-state has high oxygen affinity.

When oxygen binds to heme, it triggers a conformational change in the hemoglobin molecule, shifting it from the low-affinity T-state to the high-affinity R-state.

When heme is free of oxygen, it has a domed structure, and the iron atom is outside the plane of the heme group. When oxygen binds, the heme becomes planar, and the iron atom moves into the plane of the heme, pulling the proximal histidine along with it.

This change in the heme group triggers changes in the tertiary structure of individual hemoglobin subunits and breaks electrostatic bonds between the chains. This ultimately leads to an increase in oxygen affinity.