MCAT Biology : Properties of Carbohydrates
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Example Question #5 : Carbohydrates
Which carbon in a carbohydrate determines whether a human is capable of digesting it properly?
The first chiral carbon
All chiral carbons affect its digestion capabilities
The anomeric carbon
The carbonyl carbon
The first chiral carbon
Humans are only capable of digesting the "D" isomer of a carbohydrate. The carbon that determines whether a carbohydrate is "D" or "L" is the first chiral carbon in the sugar. If it points to the right, the sugar can be digested by humans.
Example Question #1 : Carbohydrates
Which type of bond is created between carbohydrates and the sidechain amine of select asparagine residues in proteins?
O-glycosidic
Both are correct
Neither is correct
N-glycosidic
N-glycosidic
A glycosidic bond covalently joins a carbohydrate molecule to another molecule. An O-glycosidic bond is a covalent linkage between a carbohydrate and a protein, joining a serine or threonine hydroxyl side chain and a sugar (oxygen in the bond yields "O"). An N-glycosidic linkage involves bonding of a carbohydrate and a protein, joining an asparagine side chain amide and a sugar (nitrogen in the bond yields "N"). Thus, N-glycosidic is the correct answer.
Example Question #6 : Carbohydrates
Which of the following statements is true concerning glucose polymers?
Starch is a glucose polymer held together by an 
Humans lack the enzyme that can break down the beta linkages in cellulose.
Humans do not eat foods that contain cellulose.
Glucose is not favored in the body in ring form.
Humans lack the enzyme that can break down the beta linkages in cellulose.
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 
Example Question #7 : 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?
Ruminants rearrange the molecular configuration of cellulose, allowing it to be digested by other enzymes
Ruminants house bacteria in their digestive tracts that are able to break down the cellulose
Ruminants create an enzyme that allows them to digest cellulose
Ruminants have four stomachs which allow them to digest food for a much longer time
Ruminants have a stomach pH of roughly 2.5
Ruminants house bacteria in their digestive tracts that are able to break down the cellulose
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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