Biochemistry Study Notes: Proteins

Globular proteins are not packed well due to containing different structures inside, unlike fibrous proteins that have repeated identical secondary structures.

Myoglobin is a monomeric protein primarily found in muscle tissue, containing a prosthetic heme group, and essential for oxygen storage.

Hemoglobin is a protein responsible for transporting oxygen and carbon dioxide in the blood, while also playing a role in blood buffering.

Myoglobin has a higher affinity for oxygen due to its storage function. It needs to bind O2 for longer periods than hemoglobin, which is only a transporter.

The heme group is a flat molecule with four pyrrole rings and a central iron atom. It's crucial for oxygen binding in both myoglobin and hemoglobin.

Hemoproteins are proteins that contain a heme group, a non-protein group tightly bound to the protein. Their function is determined by the protein environment.

Iron in the heme group can form up to six bonds. In myoglobin and hemoglobin, it forms four bonds with the nitrogen of the pyrrole rings, one bond with the nitrogen of a proximal histidine, and one with oxygen.

Oxidation of iron in heme to the ferric (Fe3+) state prevents normal oxygen binding.

Classification of heme based on the number of bonds formed by the iron atom.

The heme group sits within a hydrophobic pocket in the protein, stabilized by hydrophobic attractions.

The hydrophobic pocket prevents the oxidation of iron in the heme, ensuring it remains in the Fe2+ state and can bind oxygen.

The proximal histidine (F8) binds to the iron in the heme, while the distal histidine (E7) acts as a gate, controlling oxygen access to the heme.

The binding of oxygen to myoglobin follows a hyperbolic saturation curve, indicating a high affinity for oxygen.

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

Myoglobin has a high affinity for oxygen, meaning it readily binds to oxygen even at low oxygen partial pressures.

The hydrophobic interior of myoglobin prevents oxidation of iron in the heme group, allowing it to bind oxygen repeatedly.

When oxygen binds to myoglobin, the iron in the heme group shifts to a specific position within the heme pocket.

Carbon dioxide does not bind to the same site as oxygen on the heme group. It binds to the N-terminals of the protein.

Carbon monoxide (CO) can bind to the heme group in myoglobin with much higher affinity than oxygen, leading to decreased oxygen levels in the body.

The distal histidine (E7) influences the angle at which oxygen binds to the heme group in myoglobin.

A more perpendicular orientation of oxygen binding to the heme group in myoglobin results in higher affinity, while a tilted orientation has lower affinity.

The tilted orientation of oxygen binding to the heme group in myoglobin allows for easier release of oxygen when needed.

The distal histidine (E7) in myoglobin helps to prevent the binding of carbon monoxide (CO) to the heme group.

The heme group is responsible for the characteristic red color of blood.

Myoglobin is a globular protein, meaning it adopts a compact, spherical shape.

The shape of the myoglobin molecule is crucial for its function in storing oxygen and transporting it to the muscles.