MCAT Biology : Macromolecules

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #121 : Macromolecules

Which of the following statements is true concerning glucose polymers?

Possible Answers:

Humans do not eat foods that contain cellulose.

Starch is a glucose polymer held together by an -(1,6) linkage.

Humans lack the enzyme that can break down the beta linkages in cellulose.

Glucose is not favored in the body in ring form.

Correct answer:

Humans lack the enzyme that can break down the beta linkages in cellulose.

Explanation:

Glucose is the primary carbohydrate absorbed by humans, and exists for its majority of time in the body in ring form. Humans are only capable of digesting alpha linked glucose polymers, and are unable to break down beta linked polymers. As a result, cellulose is incapable of being broken down by humans.

Starch is formed by an -1,4 linkage, while glycogen is formed by an -1,6 linkage. Both of these can be digested, as they do not contain beta linkages.

Example Question #1 : Carbohydrates

Cellulose is a type of carbohydrate used in plants to store glucose. Cellulose cannot be broken down by humans, but is able to be digested by ruminants (cows for example). What is the best explanation for why ruminants are able to digest cellulose?

Possible Answers:

Ruminants have four stomachs which allow them to digest food for a much longer time

Ruminants house bacteria in their digestive tracts that are able to break down the cellulose

Ruminants have a stomach pH of roughly 2.5

Ruminants rearrange the molecular configuration of cellulose, allowing it to be digested by other enzymes

Ruminants create an enzyme that allows them to digest cellulose

Correct answer:

Ruminants house bacteria in their digestive tracts that are able to break down the cellulose

Explanation:

Cellulose and other polysaccharides with beta linkages can only be broken down by bacteria. As a result, cows have a symbiotic relationship with bacteria that live in their digestive systems.

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