Biochemistry : Identifying Specific Carbohydrate Structures

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #1 : Identifying Specific Carbohydrate Structures

Which if the following statements about glucose is false?

Possible Answers:

None of the other answers is false.

The anomeric effect has an influence on glucose’s mutarotation.

It cannot isomerize into fructose

It has the same molecular mass as fructose

In an aqueous solution, glucose can be found in open-chain, pyranose, or furanose form

Correct answer:

It cannot isomerize into fructose

Explanation:

Glucose and fructose have the same constituent atoms, so they have the same molecular mass (about ). Glucose exists in aqueous solution in an equilibrium of open-chain and several cyclic isomer forms, the most common of which is pyranose, but also one of which is furanose. Upon forming a ring structure, glucose may take one of two anomers, alpha or beta. The relative proportion of the mutarotated beta form is increased versus the alpha form because the beta anomer is such that all non hydrogen substituents are in the equitorial position. Glucose can indeed be isomerized into fructose; this is part of glycolysis.

Example Question #2 : Identifying Specific Carbohydrate Structures

The molecule sucrose is shown below

Sucrose

What is the full name for this molecule? 

Possible Answers:

-D-glucopyranosyl-(12)--D-fructofuranoside

-D-glucopyranosyl-(12)--D-fructofuranoside

None of these

-D-glucopyranosyl-(12)--D-fructopyranoside

-D-glucopyranosyl-(14)--D-fructofuranoside

Correct answer:

-D-glucopyranosyl-(12)--D-fructofuranoside

Explanation:

Sucrose is the molecule shown below(in Haworth projection). 

Sucrose

We recognize that it's a disaccharide, and that the first molecule is -D-glucopyranose. The bond to the second monosaccharide (fructose) is tricky because the glycosidic bond is going to the anomeric carbon of fructose. Therefore, this is a 1-2 linkage. Finally, since the anomeric carbon of fructose is pointing in the same direction as the 6th carbon, this is a -D-fructopyranose.

Example Question #3 : Identifying Specific Carbohydrate Structures

Which of the following sugars is lactose? 

Possible Answers:

Beta-D-glucopyranosyl-1,4-D-glucopyranose

Beta-D-galactopyranosyl-(1,4)-D-glucopyranose

Alpha-D-galactopyranosyl-(1,4)-D-glucopyranose

 

Beta-L-galactopyranosyl-1,4-D-glucopyranose

Correct answer:

Beta-D-galactopyranosyl-(1,4)-D-glucopyranose

Explanation:

Lactose is made by joining a  galactose to a glucose via a  carbon pathway. Both sugars are D-sugars. 

Example Question #70 : Identifying Biochemical Molecules

What is the difference between two carbohydrates that are epimers and two carbohydrates that are anomers?

Possible Answers:

The location of the change in configuration 

The shape of the ring

The number of carbons that have differences in configuration

The number of rings

Correct answer:

The location of the change in configuration 

Explanation:

A set of anomers will differ in the configurations of their carbonyl carbons only while a set of epimers will differ in configuration in only one carbon that is not the carbonyl carbon.

Example Question #3 : Identifying Specific Carbohydrate Structures

Glucose and galactose share a chemical formula and are known as epimers.

What is the difference between glucose and galactose?

Possible Answers:

Galactose is a ketose

Galactose is spread further apart than glucose

They differ in configuration around the fourth carbon

Glucose is bigger than galactose

Correct answer:

They differ in configuration around the fourth carbon

Explanation:

As a pair of epimers, this means that both glucose and galactose are the same in configuration in all carbons except for one non-carbonyl carbon. To differ in the configuration of the carbonyl carbon makes an anomer not an epimer. Both glucose and galactose are aldoses.

Example Question #4 : Identifying Specific Carbohydrate Structures

The following are the common substrates, enzymes and the associated products.  

Although cellulose provides the same carbohydrates as maltose, it cannot be broken down by humans. What type of linkage prevents humans from breaking down the polysaccharide?

Possible Answers:

Beta-1,4 glycosidic bond

Alpha-1,6 glycosidic bond

None of these

Beta-1,6 glycosidic bond

Alpha-1,4 glycosidic bond

Correct answer:

Beta-1,4 glycosidic bond

Explanation:

The beta-1,4 glycosidic bond is not a substrate for any human enzymes, and is thus left untreated.

Example Question #72 : Identifying Biochemical Molecules

Which of the following enzymes is correctly paired with its products and substrates? 

Possible Answers:

Correct answer:

Explanation:

An easy way to distinguish the substrate and the product from the enzyme is that the enzyme will end in "ase".  The following are the common substrates, enzymes and the associated products.  

Example Question #73 : Identifying Biochemical Molecules

Which of the following enzymes is correctly paired with its products and substrates?

Possible Answers:

Correct answer:

Explanation:

An easy way to distinguish the substrate nd the product from the enzyme is that the enzyme will end in "ase".  The following are the common substrates, enzymes and the associated products.  

Example Question #5 : Identifying Specific Carbohydrate Structures

Which of the following enzymes is correctly paired with its products and substrates?

Possible Answers:

Correct answer:

Explanation:

An easy way to distinguish the substrate and the product from the enzyme is that the enzyme will end in "ase".  The following are the common substrates, enzymes and the associated products.  

Example Question #75 : Identifying Biochemical Molecules

 

 

Which of the following enzymes is correctly paired with its products and substrates? 

 

Possible Answers:

All of these

Correct answer:

Explanation:

An easy way to distinguish the substrate and the product from the enzyme is that the enzyme will end in "ase".  The following are the common substrates, enzymes and the associated products.  

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