Question

During the process of blood coagulation, vitamin \(K\) heips in (a) the formation of thromboplastin (b) the conversion of fibrinogen to fibrin (c) the conversion of prothrombin to thrombin (d) the formation of prothrombin.

Short answer

Vitamin K is primarily involved in the synthesis of clotting factors necessary for coagulation, which includes aiding in the conversion of prothrombin to thrombin (c).

Step-by-step solution

Understanding the role of Vitamin K

Vitamin K is crucial in the blood coagulation process. It plays a major role in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate (Gla) residues. The Gla residues are essential for the binding of calcium and are necessary for the clotting factors to function.

Identifying the clotting factors

Prothrombin, or Factor II, is a protein that is dependent on vitamin K for its synthesis. Vitamin K ensures that prothrombin has the ability to bind calcium, which is required during the coagulation cascade.

Distinguishing the specific role in the given options

While Vitamin K is involved in several steps of the coagulation process, it's specific role directly relates to the synthesis of various clotting factors, including prothrombin. Vitamin K does not directly mediate the conversion of fibrinogen to fibrin or the formation of thromboplastin but is integral to the conversion of prothrombin to thrombin.

Key concepts

Prothrombin Synthesis

Prothrombin, also known as Factor II, is a vital protein in the blood coagulation process. Its synthesis is highly vitamin K-dependent. To understand this dependency, we need to dig into the liver, where prothrombin is produced. Vitamin K plays a pivotal role in modifying certain proteins required for blood clotting. Without adequate vitamin K, the liver produces prothrombin with a reduced ability to bind calcium—an essential step for activating the coagulation cascade.

In the absence of this vitamin, the blood's capacity to clot is significantly impaired, posing a risk of excessive bleeding. Thus, ensuring an adequate intake of vitamin K is crucial for maintaining normal prothrombin levels and effective coagulation.

Carboxylation of Glutamate Residues

Carboxylation of glutamate residues is a biochemical modification where vitamin K adds a carboxyl group to the amino acid glutamate in proteins. This process transforms glutamate into gamma-carboxyglutamate (Gla). Gla residues have a strong affinity for calcium ions, which are essential for the activities of various clotting factors.

During blood coagulation, Gla residues on factors like prothrombin help to anchor these proteins to phospholipid membranes in close proximity to the site of injury. This localization is crucial for the proper assembly and function of the coagulation complexes. Vitamin K's role in facilitating this process underscores the interconnectedness of nutrition and the body's ability to protect itself from bleeding.

Clotting Factors in Coagulation

Clotting factors are proteins that work in a sequential manner to form a blood clot. Prothrombin (Factor II) is just one member of a complex cast that includes Factors VII, IX, and X, which are also vitamin K-dependent. During the coagulation cascade, these factors are sequentially activated, culminating in the conversion of prothrombin to thrombin by the prothrombinase complex.

This activation of prothrombin to thrombin (which is answer option (c) in the given exercise) then leads to the transformation of soluble fibrinogen into fibrin—a mesh that traps blood cells to form the stable clot. Vitamin K's role in maintaining the functional integrity of these clotting factors is thus essential for the successful arrest of bleeding and the initiation of wound healing.