MCAT Biology : Carbohydrates
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Example Questions
Example Question #1 : Types Of Carbohydrates
Drain cleaners a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.
A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:
Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:
In contrast to the proteins in Reactions 1 and 2, the body uses carbohydrates __________.
to store energy for immediate use
to create strucutral elements of cells
to store energy for use over many days
to function as a secondary energy source after fatty acids have been oxidized
to dissolve nonpolar solutes in blood
to store energy for immediate use
Carboydrates are the main energy currency of cells. They are typically burned first, before fats and proteins, to generate energy. Proteins, in contrast, are usually the functional biomolecules, serving structural and enzymatic roles.
Example Question #2 : Types Of Carbohydrates
Which of the following accurately describes glucose?
Ketohexose
Aldohexose
Ketopentose
Aldopentose
Aldohexose
Glucose is composed of six carbons. When not in ring form, there is an aldehyde at the end of the molecule. As a result, glucose is an example of an aldohexose.
Example Question #1 : Types Of Carbohydrates
Which of the following carbohydrates is created in animals, but not in plants?
Amylose
Starch
Cellulose
Glycogen
Glycogen
Glucose is stored in animals cells in the form of glycogen. Plants store glucose as either starch or cellulose. Amylose is a specialized component of starch, and plays a key role in plant energy storage.
Plants do not form glycogen, similar to the way that humans cannot form (or break down) cellulose.
Example Question #1 : Types Of Carbohydrates
Which of the following statements is true concerning glucose?
D-glucose has the highest chiral carbon's hydroxyl group pointing to the left
The 6th carbon attacks the carbonyl carbon in order to create the cyclic structure of glucose
Maltose and cellulose differ by the type of linkage between the glucose monomers
Maltose and cellulose differ by the type of linkage between the glucose monomers
Maltose and cellulose are both composed of glucose monomers that are combined in a 1,4 glycosidic linkage, however they differ by the type of 1,4 linkage used. Cellulose uses a beta 1,4 linkage, while maltose uses an alpha 1,4 linkage.
Example Question #1 : 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?
N-glycosidic
O-glycosidic
Both are correct
Neither is correct
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 #1 : Properties Of Carbohydrates
Which of the following statements is true concerning glucose polymers?
Humans lack the enzyme that can break down the beta linkages in cellulose.
Glucose is not favored in the body in ring form.
Starch is a glucose polymer held together by an 
Humans do not eat foods that contain cellulose.
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 #2 : Properties Of 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 have four stomachs which allow them to digest food for a much longer time
Ruminants create an enzyme that allows them to digest cellulose
Ruminants have a stomach pH of roughly 2.5
Ruminants house bacteria in their digestive tracts that are able to break down the cellulose
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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