Biochemistry : Identifying Biochemical Molecules

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #41 : Identifying Biochemical Molecules

Identify the aldose pictured, including its alpha or beta designation. 

A d mannose

Possible Answers:

-D-ribose

-D-mannose

-D-glucose

-D-glucose

-D-mannose

Correct answer:

-D-mannose

Explanation:

The structure pictured is mannose because the hydroxyl groups at carbons 2, 3, and 4 are situated cis, cis, and trans (respectively) to the  attached to carbon 5.

The mannose pictured is in alpha form because the hydroxyl group at carbon 1 is trans to the  attached to carbon 5.

Example Question #2 : Help With Organic Carbohydrates

The Fischer projection pictured is a form of glucose. The carbon labeled "x" is the chiral carbon farthest away from carbon 1 and the hydroxyl group connected to carbon "x" is on the right. This fact designates that the glucose as what configuration? 

D configuration

Possible Answers:

L

Beta

D

Pyranose

Alpha

Correct answer:

D

Explanation:

The chiral carbon farthest away from carbon 1 is designated as "D" if its hydroxyl group is on the right side in the Fischer projection. In other words, this is D-glucose because the hyroxyl group on carbon "x" is oriented to the right.

Example Question #42 : Identifying Biochemical Molecules

What is the name of the aldose pictured in this Fischer projection?

D ribose

Possible Answers:

L-fructose

D-arabinose

L-xylose

D-ribose

L-lyxose

Correct answer:

D-ribose

Explanation:

The structure is D-ribose because it is a five-carbon aldose with the hydroxyl groups on carbons 2, 3, and 4 all on the right in the Fischer projection.

Example Question #41 : Identifying Monomers And Dimers

Which of the following is not a monosaccharide?

Possible Answers:

Galactose

Lactose

All of these are monosaccharides

Fructose

Glucose

Correct answer:

Lactose

Explanation:

While glucose, galactose, and fructose are all monosaccharides, lactose is a disaccharide comprised of two monosaccharides, glucose and galactose, joined by a -1,4-glycosidic bond.

Example Question #42 : Identifying Monomers And Dimers

L-Glucose is found as 2 different hexose stereoisomers in solution:  and  glucose. 

Suppose both  and  L-glucose were polymerized into long  glycosidic linkages. Which of the two polymers could be catabolized (broken down into component parts) by a human? 

Possible Answers:

-L-glucose

Neither stereoisomer

Both stereoisomers

-L-glucose

Correct answer:

Neither stereoisomer

Explanation:

In nature, L-sugars are indigestible by humans. In the case of L-glucose, even though our bodies can break down polymers of -D-glucose, it cannot digest L-glucose. 

Example Question #15 : Identifying Monosaccharides

Which of the following compounds is not a monosaccharide?

Possible Answers:

Glucose

Galactose

Fructose

Lactose

Ribose

Correct answer:

Lactose

Explanation:

Out of all the sugars listed, lactose is the only one that is not a monosaccharide. Lactose is composed of a glucose and galactose bound together in a glycosidic linkage.

Example Question #13 : Identifying Monosaccharides

Which sugar is another name for "blood sugar?"

Possible Answers:

Lactose

Glucose

Sucrose

Fructose

Correct answer:

Glucose

Explanation:

Glucose is also called "blood sugar" because it is the main sugar found in our blood. Sucrose is what we know as "table sugar" because it is commonly found in our kitchens and used in baking etc. Fructose is also known as "fruit sugar" because it occurs in naturally-occurring fruits, giving them their sweetness. Lactose is sometimes called "milk sugar" because it is found in milk.

Example Question #1 : Identifying Disaccharides

Which of the following is not a disaccharide?

Possible Answers:

All of these are disaccharides

Sucrose

Maltose

Lactose

Cellobiose

Correct answer:

All of these are disaccharides

Explanation:

Review the specific types of monosaccharides and glycosidic bonds that are involved in these disaccharides. Remember that disaccharides are formed upon dehydration synthesis of two monosaccharides.

Maltose is composed of two glucose monomers with an 1-4 linkage.

Cellobiose is composed of two glucose monomers with a 1-4 linkage.

Sucrose is composed of one glucose monomer and one fructose monomer with an 1-2 linkage.

Lactose is composed of one galactose monomer and one glucose monomer with a 1-4 linkage.

Example Question #1 : Identifying Disaccharides

Maltose is a disaccharide composed of which two monosaccharides?

Possible Answers:

Galactose + galactose

Glucose + fructose

Glucose + glucose

Fructose + fructose

Glucose + galactose

Correct answer:

Glucose + glucose

Explanation:

Maltose, which is made up of two glucose monomers joined by an alpha-1,4 linkage, is the correct answer. On the other hand, lactose is made up of one glucose monomer and one galactose monomer, and sucrose is made up of one glucose monomer and one fructose monomer. 

Example Question #2 : Identifying Disaccharides

Which of the following substances are found in fructose?

Possible Answers:

Galactose

None of these are found in fructose

Lactose

Glucose

Correct answer:

None of these are found in fructose

Explanation:

Fructose is a monosaccharide; therefore, it is only made up of one type of carbohydrate. Disaccharides are made up of two types of monosaccharides. For example, lactose is made up of galactose and glucose whereas sucrose is made up of glucose and fructose. Polysaccharides are made up of multiple units of monosaccaharides.

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