Question

The anticlotting property of heparin is partly the result of the negative charges it carries. (a) Identify the functional groups that provide the negative charges. (b) Which type of heparin is a better anticoagulant, one with a high or a low degree of polymerization?

Short answer

Answer: The functional groups in heparin that carry a negative charge are carboxylate (-COO-) and sulfate (-OSO3-) groups. A higher degree of polymerization in heparin results in a longer chain with more monomers, which leads to more negative charges carried by these functional groups. This enhances heparin's ability to bind with antithrombin, making it a better anticoagulant than heparin with a lower degree of polymerization.

Step-by-step solution

(a) Identifying the functional groups with negative charges)

To identify the functional groups with negative charges, we must first look at the structure of heparin. Heparin is a complex polysaccharide made up of alternating residues of D-glucosamine and L-iduronic acid or D-glucuronic acid. The functional groups that provide negative charges in heparin are carboxylate and sulfate groups. Carboxylate groups (-COO-) are present in the uronic acid residues, L-iduronic acid, or D-glucuronic acid, and they carry a negative charge. Sulfate groups (-OSO3-) are present on the D-glucosamine residues, and they also carry a negative charge. These negatively charged functional groups contribute to the anticlotting properties of heparin.

(b) Comparing anticoagulant properties of heparin with high and low degree of polymerization)

The degree of polymerization refers to the number of monomers (sugar units, in case of heparin) linked together in a chain. The anticoagulant properties of heparin are known to be more efficient in heparin with a higher degree of polymerization. This is because a higher degree of polymerization in heparin indicates a longer chain with more monomers, which results in more negative charges carried by the carboxylate and sulfate groups. The more negatively charged a heparin molecule is, the better it can bind with antithrombin, which is a key protein in blood clotting. Thus, a heparin with a high degree of polymerization would be a better anticoagulant than one with a low degree of polymerization.