Question

Glycosaminoglycans A. are the carbohydrate portion of glycoproteins. B. contain large segments of a repeating unit typically consisting of a hexosamine and a uronic acid. C. always contain sulfate. D. exist in only two forms. E. are bound to protein by ionic interaction.

Short answer

Answer: The correct statements are options B and E. They state that glycosaminoglycans contain large segments of a repeating unit typically consisting of a hexosamine and a uronic acid (Option B), and glycosaminoglycans are bound to protein by ionic interaction (Option E).

Step-by-step solution

Option A: Glycosaminoglycans are the carbohydrate portion of glycoproteins

Glycosaminoglycans are long, unbranched polysaccharides consisting of repeating disaccharide units, usually composed of an amino sugar and a uronic acid. This description is different from glycoproteins, as glycoproteins are proteins that have carbohydrates (mostly oligosaccharides) attached to them. Therefore, option A is incorrect.

Option B: Glycosaminoglycans contain large segments of a repeating unit typically consisting of a hexosamine and a uronic acid

As mentioned earlier, glycosaminoglycans are composed of repeating disaccharide units, where one unit is usually a hexosamine (an amino sugar) and the other one is a uronic acid. This is in line with the given statement. Thus, option B is correct.

Option C: Glycosaminoglycans always contain sulfate

While some glycosaminoglycans do contain sulfate groups, not all of them do. An example of a glycosaminoglycan without sulfate is hyaluronan. As such, option C is incorrect.

Option D: Glycosaminoglycans exist in only two forms

There are several different forms of glycosaminoglycans found in various organisms. Some well-known examples are heparin, heparan sulfate, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Hence, option D is incorrect, as glycosaminoglycans exist in more than two forms.

Option E: Glycosaminoglycans are bound to protein by ionic interaction

Glycosaminoglycans can indeed be bound to proteins through ionic or covalent interactions to form proteoglycans. Ionic interactions are generally weaker and more dynamic than covalent ones, but they still occur. Therefore, option E is correct. In conclusion, the correct statements for this exercise are options B and E.