Question

Read the following statements and select the correct option. Statement 1: Prothrombin is essential for blood clotting. Statement 2 : Prothrombin is synthesized in the liver in the presence of \(\mathrm{Ca}^{+*}\), (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement \(1 .\) (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1 . (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect.

Short answer

Both Statement 1 and Statement 2 are correct regarding prothrombin's role, but Statement 2 does not correctly identify its synthesis requirements and is not the correct explanation for Statement 1. Therefore, the correct option is (b).

Step-by-step solution

Verify Statement 1

Statement 1 asserts that 'Prothrombin is essential for blood clotting.' This is a factual statement in biology, as prothrombin is a protein that plays an important part in blood coagulation. It is converted to thrombin during the clotting process, which is essential for forming a blood clot. Thus, Statement 1 is correct.

Verify Statement 2

Statement 2 indicates that 'Prothrombin is synthesized in the liver in the presence of \(\mathrm{Ca}^{+*}\),'. This statement is partially correct; prothrombin is indeed synthesized in the liver, but the 'presence of \(\mathrm{Ca}^{+*}\)' is misleading. Vitamin K and not calcium ions is the critical cofactor required for the synthesis of prothrombin in the liver. Calcium ions are required later in the clotting cascade to aid in various steps, including the final conversion of prothrombin into active thrombin. However, it is not directly involved in the synthesis of prothrombin. Thus, Statement 2 is not entirely correct as written.

Determine the Relation Between Statements 1 and 2

Even if we presume Statement 2 was referring correctly to the role of calcium in clotting, the role of calcium would be in the clotting mechanism rather than in explaining the necessity of prothrombin in blood clotting. Therefore, even though both statements refer to elements of the blood clotting process, Statement 2 would not be the correct explanation of why prothrombin is essential as declared in Statement 1.

Key concepts

Prothrombin Function

The role of prothrombin in blood clotting is crucial and multifaceted. Prothrombin, or factor II, is a protein produced by the liver that circulates in the bloodstream in an inactive form. When an injury occurs and a blood vessel is damaged, the clotting cascade is initiated.

This cascade is a series of steps that involve various proteins and factors, which ultimately leads to the conversion of prothrombin into thrombin by the action of activated factor X, in a complex called prothrombinase. Thrombin is a key enzyme that transforms fibrinogen into fibrin, which forms the meshwork that stabilizes the clot.

Understanding prothrombin's function helps us appreciate its role in stemming blood loss and initiating tissue repair. However, aberrations in its activity can lead to inadequate clotting or excessive clot formation, resulting in conditions such as hemophilia or thrombosis, respectively.

Blood Coagulation

Blood coagulation, also known as clotting, is the process that stops bleeding when an injury occurs. It is a highly regulated process that involves multiple steps and factors. When a blood vessel is injured, platelets are the first responders, forming a plug at the injury site.

This is followed by the coagulation cascade, which has two pathways: the intrinsic and extrinsic pathways that converge on a common pathway. The common pathway involves the activation of factor X, which, with the assistance of factor V, calcium ions, and phospholipids, forms the prothrombinase complex that converts prothrombin to thrombin.

Subsequently, thrombin facilitates the conversion of fibrinogen to fibrin, which interlaces to form a stable clot. A balance between clot formation and dissolution is essential for health, as disruptions can lead to either uncontrolled bleeding or dangerous clot formation.

Liver Synthesis of Clotting Factors

The liver is a central player in the synthesis of clotting factors, including prothrombin. The liver cells, or hepatocytes, produce most of the plasma proteins required for blood clotting. The synthesis of these factors is vitamin K-dependent, which serves as a vital cofactor.

Vitamin K plays a critical role in a post-translational modification process known as gamma-carboxylation, which is essential for the clotting factors to bind to negatively charged phospholipid surfaces of cells and be functional. Adequate vitamin K levels, therefore, are crucial for the synthesis of prothrombin and other factors like VII, IX, and X.

Patients with liver diseases or vitamin K deficiency due to poor nutrition or long-term antibiotics use can have impaired clotting factor synthesis, leading to an increased risk of bleeding. This underscores the liver's importance in maintaining hemostasis in the body.