Blood and Body Fluids (BLF) 103 Quiz: Hemoglobin

Proteins that contain heme as a tightly bound prosthetic group. These proteins are crucial for various functions in the body, including oxygen transport, detoxification, and electron transfer.

A protein found in red blood cells that binds to oxygen in the lungs and transports it to tissues throughout the body. It consists of four polypeptide chains, each containing a heme group.

A protein found in muscle tissue that stores oxygen. It consists of a single polypeptide chain and a heme group.

A non-protein molecule that contains an iron ion at its center and is responsible for binding oxygen. It is made up of a porphyrin ring with a ferrous iron atom in the center.

A molecule that binds to hemoglobin and reduces its affinity for oxygen, allowing for increased oxygen delivery to tissues. It plays a crucial role in regulating oxygen delivery during exercise.

The major hemoglobin found in fetuses, consisting of two alpha and two gamma chains (α2γ2). It has a higher affinity for oxygen compared to adult hemoglobin. It gradually disappears after birth and is replaced by HbA by 6 months of age.

The most abundant type of hemoglobin in adults, comprising 98% of total hemoglobin. It consists of two alpha and two beta chains (α2β2).

A minor form of hemoglobin in adults, making up about 2% of total hemoglobin. Composed of two alpha and two delta chains (α2δ2).

A glycated form of hemoglobin A1, formed by the slow and non-enzymatic attachment of glucose to hemoglobin. Its concentration is proportional to average blood glucose levels over the preceding 3 months. It is used to monitor diabetic patients.

A molecule that binds to hemoglobin in red blood cells, promoting oxygen delivery to tissues. It stabilizes the T-conformation of hemoglobin, which decreases oxygen affinity.

Hemoglobin is a protein found in red blood cells that binds to oxygen in the lungs, where oxygen concentration is high, and transports it to tissues and organs for cellular respiration.

Each hemoglobin molecule can bind to a maximum of four oxygen molecules, facilitating efficient oxygen transport throughout the body.

Hemoglobin also plays a crucial role in carbon dioxide (CO2) transport, helping to remove this metabolic waste product from tissues to the lungs for exhalation.

Hemoglobin can bind to carbon dioxide directly or indirectly by buffering hydrogen ions (H+).

Hemoglobin acts as a buffer by binding to hydrogen ions (H+), helping to maintain blood pH within a narrow range (7.35–7.45).

Heme is a complex organic ring structure called protoporphyrin IX that contains a single iron atom (Fe2+) in its ferrous state. The iron atom binds to the porphyrin ring and forms the core of a hemoglobin molecule.

The iron atom in heme has six coordination bonds. Four bonds are to nitrogen atoms within the porphyrin ring, the fifth is to a histidine residue in the globin chain, and the sixth is available to bind oxygen.

The iron atom in heme is normally in the ferrous (Fe2+) state. The coordinated nitrogen atoms in heme prevent the iron from being oxidized to the ferric (Fe3+) state, which cannot bind oxygen.

The heme group, a crucial component of myoglobin and hemoglobin, is located within a pocket in the globin chain. This protects it from reacting with other molecules in a way that could damage its function.

When free heme in solution is exposed to oxygen, two heme molecules can bind to a single oxygen molecule. This process oxidizes the iron in heme to Fe3+, rendering it unable to bind to oxygen.

One histidine residue (His F8) forms a bond with the heme group through its imidazole group. Hydrophobic interactions with nonpolar amino acids also contribute to heme's attachment to the globin chain.

Oxygen binding to the heme group in hemoglobin leads to a structural change in the molecule. This change ruptures some hydrogen and ionic bonds between the α2β2 dimers, resulting in a more relaxed conformation known as the 'R form'.

Hemoglobin exists in two distinct conformational states: the T form (tense) and the R form (relaxed). The T form is characterized by more ionic and hydrogen bonds, resulting in a less mobile dimer with a lower affinity for oxygen. The R form has fewer ionic bonds, making it more mobile with a higher affinity for oxygen.

The binding of oxygen to one subunit of deoxyhemoglobin facilitates the binding of oxygen to other subunits. This phenomenon is known as cooperative binding. As oxygen dissociates from fully oxygenated hemoglobin, it becomes easier for other oxygen molecules to detach from the remaining subunits.

The first oxygen molecule binds weakly to a subunit of deoxyhemoglobin in the T state. This initial binding triggers a conformational change in the molecule, shifting it towards the R state. The subsequent oxygen molecules bind more readily to the subunits in the R state due to the increased affinity caused by the conformational shift.

Cooperative binding of oxygen to hemoglobin ensures efficient oxygen delivery to tissues. When hemoglobin encounters a high partial pressure of oxygen in the lungs, it readily binds oxygen. In the tissues, where oxygen pressure is lower, hemoglobin releases oxygen readily to the cells. This process is crucial for oxygen transport throughout the body.

The cooperative binding of oxygen to hemoglobin can be represented as a sigmoidal curve. This curve illustrates the gradual increase in oxygen affinity as more oxygen molecules bind to the hemoglobin molecule.