Biochemistry : Identifying Biochemical Molecules

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #14 : Identifying Specific Carbohydrate Structures

Identify the given structure.

D mannose

Possible Answers:

D-gulose

D-alrose

D-mannose

D-allose

D-glucose

Correct answer:

D-mannose

Explanation:

D-mannose is an aldohexose. Aldo indicates the aldehyde on the first carbon and the hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

Example Question #15 : Identifying Specific Carbohydrate Structures

Identify the given structure.

D ribose

Possible Answers:

D-glucose

D-sucrose

D-ribulose

D-ribose

D-mannose

Correct answer:

D-ribose

Explanation:

D-ribose is an aldopentose. Aldo indicates the aldehyde on the first carbon and the pentose indicates a five-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

Example Question #16 : Identifying Specific Carbohydrate Structures

Identify the given structure.

D sorbose

Possible Answers:

L-sorbose

D-fructose

L-fructose

D-sorbose

D-glucose

Correct answer:

D-sorbose

Explanation:

The pictured ketohexose is D-sorbose. Keto indicates the ketone present on carbon number two and hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

Example Question #17 : Identifying Specific Carbohydrate Structures

Identify the carbohydrate class of the given molecule.

D fructose

Possible Answers:

Aldopentose

Ketalhexose

Ketopentose

Aldohexose

Ketohexose

Correct answer:

Ketohexose

Explanation:

The structure is of a ketohexose. Keto- refers to the ketone at the second carbon and hexose refers to a carbohydrate with six carbons.

Example Question #18 : Identifying Specific Carbohydrate Structures

Identify the carbohydrate class of the given molecule.

D galactose

Possible Answers:

Ketopentose

Ketohexose

Hemiketose

Aldohexose

Aldopentose

Correct answer:

Aldohexose

Explanation:

The structure is of an aldohexose. Aldo- refers to the aldehyde at the first carbon, and the hexose refers to a carbohydrate with six carbons.

Example Question #31 : Identification By Structure

Identify the carbohydrate class of the given molecule.

D ribose

Possible Answers:

Aldopentose

Aldoquintos

Aldohexose

Ketohexose

Ketopentose

Correct answer:

Aldopentose

Explanation:

The structure is an aldopentose. Aldo- refers to the aldehyde at the first carbon and pentose refers to a carbohydrate with five carbons.

Example Question #31 : Identification By Structure

Identify the carbohydrate class of the given molecule.

D ribulose

Possible Answers:

Ketoquintos

Ketopentose

Ketohexose

Aldohexose

Aldopentose

Correct answer:

Ketopentose

Explanation:

The structure is a ketopentose. Keto- refers to the ketone at the second carbon and pentose refers to a carbohydrate with five carbons.

Example Question #32 : Identification By Structure

Identify the given structure.

D glucose ring

Possible Answers:

D-glucose

L-glucose

D-galactose

L-galactose

D-fructose

Correct answer:

D-glucose

Explanation:

This ring structure is of D-glucose. The hydroxyl group on the first carbon (the carbon to the bottom right of the oxygenin the ring) can face either down (the alpha conformation) or up (the beta conformation). Note that the beta conformer is more thermodynamically stable since all the hydroxyl groups on the ring would be in the equitorial position, thus minimizing steric hinderance and intramolecular electrostatic repulsion.

Example Question #33 : Identification By Structure

Identify the given structure.

D fructose ring

Possible Answers:

D-fructose

D-glucose

D-galactose

D-mannose

D-ribose

Correct answer:

D-fructose

Explanation:

This is the ring/cyclic structure of D-fructose.

Example Question #81 : Identifying Biochemical Molecules

Which of the following is the correct structure of a disaccharide?

Possible Answers:

Lactose = galactose + galactose

Sucrose = glucose + glucose

Maltose = glucose + glucose

Lactose = galactose + fructose

Maltose = sucrose + fructose

Correct answer:

Maltose = glucose + glucose

Explanation:

The correct structures of the disaccharides are:

Maltose = glucose + glucose

Sucrose = glucose + fructose

Lactose = glucose + galactose

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