Question 1

Which of the following best describes the primary biological roles of carbohydrates in living organisms?

Accepted Answer

They provide structural integrity, mediate cell signaling, and serve as energy sources.

Question 2

Which structural feature distinguishes an aldose from a ketose?

Accepted Answer

Aldose contains an aldehyde group at the end of the chain, while ketose contains a ketone group not necessarily at the end.

Question 3

How many stereoisomers are possible for an aldohexose and what is the formula used to calculate this?

Accepted Answer

16 stereoisomers; formula: $$2^n$$ where $$n is $$the number of chiral centers.

Question 4

Which of the following statements about D- and L-glucose is correct?

Accepted Answer

They are enantiomers and only D-glucose is metabolized by most biological enzymes.

Question 5

Which pair of sugars are epimers, differing only at the fourth carbon?

Accepted Answer

D-glucose and D-galactose

Question 6

What is the process called by which α- and β-glucopyranose interconvert in aqueous solution, and what is the equilibrium ratio of β to α anomer for D-glucose?

Accepted Answer

Mutarotation; approximately 64% β and 36% α

Question 7

Which of the following best describes a glycosidic bond?

Accepted Answer

A covalent bond formed between the anomeric hydroxyl group of one sugar and a hydroxyl group of another, with loss of water.

Question 8

Why are all free monosaccharides considered reducing sugars?

Accepted Answer

Because their cyclic rings can open to expose a reactive carbonyl group capable of being oxidized.

Question 9

Which glycosidic linkage is responsible for the structural rigidity and water insolubility of cellulose?

Accepted Answer

Beta(1-4) linkage

Question 10

How do the branching patterns of amylopectin and glycogen differ?

Accepted Answer

Glycogen is more highly branched, with branches every 8-12 residues, while amylopectin branches every 24-30 residues.

Question 11

A patient is diagnosed with a deficiency in the enzyme that breaks β(1-4) glycosidic bonds. Which dietary polysaccharide will they have trouble digesting?

Accepted Answer

Cellulose

Question 12

Which of the following is NOT a major class of monosaccharide derivative?

Accepted Answer

Phosphosugars

Question 13

Which type of glycosidic bond links the two monosaccharides in lactose?

Accepted Answer

Beta(1-4) bond

Question 14

Which statement correctly describes the difference between N-linked and O-linked oligosaccharides in proteoglycans?

Accepted Answer

N-linked oligosaccharides attach to the amide nitrogen of asparagine, while O-linked attach to the hydroxyl oxygen of serine or threonine.

Question 15

Which of the following best describes the physiological role of hyaluronate?

Accepted Answer

It serves as a biological lubricant and shock absorber in synovial joint fluid.

Question 16

A scientist oxidizes the primary alcohol group of a glucose molecule while keeping the aldehyde intact. Which derivative is formed?

Accepted Answer

Uronic acid

Question 17

Which of the following statements about ABO blood group antigens is correct?

Accepted Answer

A antigen has an extra N-acetylgalactosamine, B antigen has an extra galactose, and both share the H-antigen core.

Question 18

Which of the following best explains why biological enzymes selectively metabolize D-glucose but not L-glucose?

Accepted Answer

Enzymes are chiral and only fit the D-glucose configuration.

Question 19

A sugar alcohol is formed by which chemical transformation?

Accepted Answer

Reduction of the carbonyl group to a hydroxyl group.

Question 20

Which of the following is a correct application of the formula for stereoisomers ($$2^n) to a $$ketohexose?

Accepted Answer

A ketohexose has 3 chiral centers, so $$2^3 = 8$ stereoisomers.

Biochemistry: Carbohydrates – Guided Study and Step-by-Step Practice

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