GRE Subject Test: Biology : Understanding Carbohydrates
Study concepts, example questions & explanations for GRE Subject Test: Biology
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Example Questions
Example Question #1 : Understanding Carbohydrates
What factor determines whether humans are capable of digesting a polysaccharide?
The linkage between monomers
The branching pattern of the polysaccharide
The number of carbons in the carbohydrate
The number of monomers in the polysaccharide
The linkage between monomers
Carbohydrate monomers (monosaccharides) can be joined together with either alpha or beta linkages. Humans have the enzymes necessary in order to break down alpha linkages, but not beta linkages. Cellulose is a polysaccharide in which the monomers joined together by beta linkages, so humans cannot digest cellulose. Some bacterial species are capable of cleaving these linkages and have developed symbiotic or mutualistic relationships with animals. These bacterial species inhabit the mammalian digestive tract, cleaving beta linkages and gaining protection from the outside environment.
The size and branching pattern of a carbohydrate do not affect its ability to be digested.
Example Question #2 : Understanding Carbohydrates
Which polysaccharide is the primary form of energy storage in plants?
Peptidoglycan
Glycogen
Cellulose
Starch
Starch
The two most common polysaccharides found in plant cells are starch and cellulose. Starch is the primary source of energy storage, while cellulose is used to construct the plant's cell walls.
Example Question #1 : Other Macromolecules
What is the difference between the alpha and beta forms of a monosaccharide?
The orientation of the hydroxyl group on the anomeric carbon
The direction all hydroxyl groups point in the ring
The number of carbons in the ring
Whether the monosaccharide is an aldose or a ketose
The orientation of the hydroxyl group on the anomeric carbon
When a monosaccharide becomes cyclic in form, the anomeric carbon can have its hydroxyl group pointing in the same direction as the methoxy group, or oriented in the opposite direction. This orientation determines whether the sugar is considered alpha or beta.
Example Question #2 : Other Macromolecules
Two monosaccharides can be linked together to form a disaccharide. This linkage is known as a __________ bond.
Hydrogen bond
Glycosidic
Peptide
Ionic
Phosphodiester
Glycosidic
Carbohydrates are linked together to form disaccharides and other polysaccharides through glycosidic linkages. A glycosidic linkage is one in where two sugar molecules are bridged by an oxygen atom. Peptide linkages are found between amino acids and phosphodiester bonds are found between nucleic acid monomers. Ionic bonds involve the complete transfer of one or more electrons from one species to another. Hydrogen bonds are weak intermolecular and intramolecular forces that contribute to the stability of many substances such as liquid water.
Example Question #3 : Other Macromolecules
Glycogen and starch are polysaccharides connected through __________ linkages, and cellulose is connected via __________ linkages.
alpha . . . beta
beta . . . gamma
alpha . . . gamma
beta . . . alpha
alpha . . . alpha
alpha . . . beta
Glycogen and starch molecules are connected by alpha linkages. Glycogen and starch can be digested by humans because we have an enzyme capable of separating these linkages to produce monosaccharides. Cellulose on the other hand is connected through beta linkages. These beta linkages allow for the polysaccharide to form straight chains which can serve structural purposes such as plant cell walls. Cellulose, however, cannot be digested by humans because we do not have enzymes capable of severing these linkages.
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