,CHEM 210 Module 4 Exam | Biochemistry | Portage
| Q & A | 26/27 Actual (PDF)
1. A carbohydrate sample functions mainly as a rapidly mobilized cellular fuel. Which molecular feature most
directly supports that role?
A) Multiple hydroxyl groups surrounding a carbonyl-derived skeleton
B) A long hydrocarbon chain with no heteroatoms
C) A repeating peptide backbone joined by amide bonds
D) A fused four-ring steroid nucleus
Correct Answer: Multiple hydroxyl groups surrounding a carbonyl-derived skeleton
Rationale: Carbohydrates commonly contain multiple hydroxyl groups and a carbonyl-derived framework, making
many small sugars polar and readily handled in aqueous biochemical environments. Hydrocarbon chains describe
many lipids, peptide backbones define proteins, and fused four-ring systems characterize steroids rather than
carbohydrates. This structural pattern helps explain why many sugars serve as accessible energy substrates.
2. Consider two biomolecules of equal mass: a hexose and a triacylglycerol. Which statement best distinguishes the
usual biological role emphasized for the hexose?
A) It is commonly used as an immediate energy source and metabolic intermediate
B) It is primarily a long-term hydrophobic energy reserve
C) It is the principal catalyst for most cellular reactions
D) It stores hereditary information through base pairing
Correct Answer: It is commonly used as an immediate energy source and metabolic intermediate
Rationale: A hexose such as glucose is commonly used as an immediate fuel and central metabolic intermediate.
Long-term hydrophobic energy storage is more characteristic of triacylglycerols, catalysis is mainly performed by
enzymes, and hereditary information is stored in nucleic acids. The distinction links carbohydrate structure to rapid
availability in aqueous cellular chemistry.
3. Classify a monosaccharide that contains six carbons and an aldehyde functional group in its open-chain form.
A) Ketohexose
B) Aldopentose
C) Ketotriose
, D) Aldohexose
Correct Answer: Aldohexose
Rationale: An aldohexose has six carbons and an aldehyde in its open-chain form, so both parts of the name describe
the molecule correctly. A ketohexose has a ketone, an aldopentose has five carbons, and a ketotriose has only three
carbons. Correct classification requires tracking both carbon number and carbonyl type. The conclusion follows from
standard carbohydrate structure-function relationships.
4. A five-carbon sugar contains a ketone at carbon 2. Which classification is most precise?
A) Ketopentose
B) Aldopentose
C) Ketohexose
D) Aldotetrose
Correct Answer: Ketopentose
Rationale: A ketopentose contains five carbons and a ketone carbonyl, which matches the stated structure. An
aldopentose would contain an aldehyde, a ketohexose would have six carbons, and an aldotetrose would have four
carbons plus an aldehyde. The systematic name therefore captures both chain length and carbonyl identity. That
relationship is consistent with the expected chemistry of monosaccharides and their polymers.
5. During structural analysis, a three-carbon monosaccharide is found to have its carbonyl at the terminal carbon.
What is the best classification?
A) Ketotriose
B) Aldotriose
C) Aldotetrose
D) Ketohexose
Correct Answer: Aldotriose
Rationale: A terminal carbonyl in a monosaccharide is an aldehyde, and a three-carbon sugar is a triose, giving the
term aldotriose. A ketotriose has an internal ketone, while the tetrose and hexose choices have different carbon
counts. The location of the carbonyl is therefore decisive for the first part of the classification.
6. Dihydroxyacetone and glyceraldehyde contain the same number of carbons. Which feature distinguishes
dihydroxyacetone?
A) It contains six carbons instead of three
B) It lacks hydroxyl groups
C) It is a polysaccharide rather than a monosaccharide
, D) Its carbonyl is a ketone rather than an aldehyde
Correct Answer: Its carbonyl is a ketone rather than an aldehyde
Rationale: Dihydroxyacetone is a ketotriose because its carbonyl is a ketone, whereas glyceraldehyde is an
aldotriose with an aldehyde. Both have three carbons and hydroxyl groups, and both are monosaccharides rather
than polysaccharides. This comparison shows how carbonyl placement can distinguish sugars even when their
carbon counts match. This distinction is important when interpreting carbohydrate reactivity and biological function.
7. A researcher converts the aldehyde group of an aldose to an alcohol without changing the carbon skeleton.
Which defining aldose feature has been removed?
A) The chiral carbon farthest from the carbonyl
B) The terminal carbonyl group
C) Every carbon-carbon bond
D) All hydroxyl substituents
Correct Answer: The terminal carbonyl group
Rationale: An aldose is defined by a terminal aldehyde carbonyl in its open-chain form, so reducing that group to an
alcohol removes the defining carbonyl feature. The distant chiral center can remain unchanged, and neither the
carbon skeleton nor all hydroxyl groups must disappear. Functional-group identity, not simply carbon count,
determines the aldose classification.
8. Two six-carbon monosaccharides have identical formulas, but one is an aldose and the other a ketose.
What explains their relationship?
A) They are constitutional isomers with different carbonyl positions
B) They are identical molecules drawn differently
C) They are necessarily enantiomers
D) They differ only in the number of oxygen atoms
Correct Answer: They are constitutional isomers with different carbonyl positions
Rationale: An aldohexose and a ketohexose can share a molecular formula while differing in connectivity because
the carbonyl occurs at different positions. That makes them constitutional isomers, not identical drawings.
Enantiomers have the same connectivity with opposite configurations, and these sugars do not need different
oxygen counts to have distinct structures.
9. Glucose is described as a hexose. What information does the term hexose provide directly?
A) The sugar has six oxygen atoms
B) The molecule always forms a six-membered ring
| Q & A | 26/27 Actual (PDF)
1. A carbohydrate sample functions mainly as a rapidly mobilized cellular fuel. Which molecular feature most
directly supports that role?
A) Multiple hydroxyl groups surrounding a carbonyl-derived skeleton
B) A long hydrocarbon chain with no heteroatoms
C) A repeating peptide backbone joined by amide bonds
D) A fused four-ring steroid nucleus
Correct Answer: Multiple hydroxyl groups surrounding a carbonyl-derived skeleton
Rationale: Carbohydrates commonly contain multiple hydroxyl groups and a carbonyl-derived framework, making
many small sugars polar and readily handled in aqueous biochemical environments. Hydrocarbon chains describe
many lipids, peptide backbones define proteins, and fused four-ring systems characterize steroids rather than
carbohydrates. This structural pattern helps explain why many sugars serve as accessible energy substrates.
2. Consider two biomolecules of equal mass: a hexose and a triacylglycerol. Which statement best distinguishes the
usual biological role emphasized for the hexose?
A) It is commonly used as an immediate energy source and metabolic intermediate
B) It is primarily a long-term hydrophobic energy reserve
C) It is the principal catalyst for most cellular reactions
D) It stores hereditary information through base pairing
Correct Answer: It is commonly used as an immediate energy source and metabolic intermediate
Rationale: A hexose such as glucose is commonly used as an immediate fuel and central metabolic intermediate.
Long-term hydrophobic energy storage is more characteristic of triacylglycerols, catalysis is mainly performed by
enzymes, and hereditary information is stored in nucleic acids. The distinction links carbohydrate structure to rapid
availability in aqueous cellular chemistry.
3. Classify a monosaccharide that contains six carbons and an aldehyde functional group in its open-chain form.
A) Ketohexose
B) Aldopentose
C) Ketotriose
, D) Aldohexose
Correct Answer: Aldohexose
Rationale: An aldohexose has six carbons and an aldehyde in its open-chain form, so both parts of the name describe
the molecule correctly. A ketohexose has a ketone, an aldopentose has five carbons, and a ketotriose has only three
carbons. Correct classification requires tracking both carbon number and carbonyl type. The conclusion follows from
standard carbohydrate structure-function relationships.
4. A five-carbon sugar contains a ketone at carbon 2. Which classification is most precise?
A) Ketopentose
B) Aldopentose
C) Ketohexose
D) Aldotetrose
Correct Answer: Ketopentose
Rationale: A ketopentose contains five carbons and a ketone carbonyl, which matches the stated structure. An
aldopentose would contain an aldehyde, a ketohexose would have six carbons, and an aldotetrose would have four
carbons plus an aldehyde. The systematic name therefore captures both chain length and carbonyl identity. That
relationship is consistent with the expected chemistry of monosaccharides and their polymers.
5. During structural analysis, a three-carbon monosaccharide is found to have its carbonyl at the terminal carbon.
What is the best classification?
A) Ketotriose
B) Aldotriose
C) Aldotetrose
D) Ketohexose
Correct Answer: Aldotriose
Rationale: A terminal carbonyl in a monosaccharide is an aldehyde, and a three-carbon sugar is a triose, giving the
term aldotriose. A ketotriose has an internal ketone, while the tetrose and hexose choices have different carbon
counts. The location of the carbonyl is therefore decisive for the first part of the classification.
6. Dihydroxyacetone and glyceraldehyde contain the same number of carbons. Which feature distinguishes
dihydroxyacetone?
A) It contains six carbons instead of three
B) It lacks hydroxyl groups
C) It is a polysaccharide rather than a monosaccharide
, D) Its carbonyl is a ketone rather than an aldehyde
Correct Answer: Its carbonyl is a ketone rather than an aldehyde
Rationale: Dihydroxyacetone is a ketotriose because its carbonyl is a ketone, whereas glyceraldehyde is an
aldotriose with an aldehyde. Both have three carbons and hydroxyl groups, and both are monosaccharides rather
than polysaccharides. This comparison shows how carbonyl placement can distinguish sugars even when their
carbon counts match. This distinction is important when interpreting carbohydrate reactivity and biological function.
7. A researcher converts the aldehyde group of an aldose to an alcohol without changing the carbon skeleton.
Which defining aldose feature has been removed?
A) The chiral carbon farthest from the carbonyl
B) The terminal carbonyl group
C) Every carbon-carbon bond
D) All hydroxyl substituents
Correct Answer: The terminal carbonyl group
Rationale: An aldose is defined by a terminal aldehyde carbonyl in its open-chain form, so reducing that group to an
alcohol removes the defining carbonyl feature. The distant chiral center can remain unchanged, and neither the
carbon skeleton nor all hydroxyl groups must disappear. Functional-group identity, not simply carbon count,
determines the aldose classification.
8. Two six-carbon monosaccharides have identical formulas, but one is an aldose and the other a ketose.
What explains their relationship?
A) They are constitutional isomers with different carbonyl positions
B) They are identical molecules drawn differently
C) They are necessarily enantiomers
D) They differ only in the number of oxygen atoms
Correct Answer: They are constitutional isomers with different carbonyl positions
Rationale: An aldohexose and a ketohexose can share a molecular formula while differing in connectivity because
the carbonyl occurs at different positions. That makes them constitutional isomers, not identical drawings.
Enantiomers have the same connectivity with opposite configurations, and these sugars do not need different
oxygen counts to have distinct structures.
9. Glucose is described as a hexose. What information does the term hexose provide directly?
A) The sugar has six oxygen atoms
B) The molecule always forms a six-membered ring
