Biochemistry Carbohydrate Chemistry and Metabolism 1 — Questions and Answers
Question 1: Which monosaccharide is the primary fuel for the brain under normal conditions?
- Fructose
- Galactose
- Glucose (Correct answer)
- Ribose
Correct answer: Glucose
Glucose is the brain's primary energy substrate under normal fed conditions, as the blood-brain barrier limits the transport of most other fuels.
Question 2: The anomeric carbon of glucose is carbon number:
- C-1 (Correct answer)
- C-2
- C-3
- C-6
Correct answer: C-1
C-1 of glucose is the anomeric carbon, the former carbonyl carbon that becomes the new chiral center when the open-chain form cyclizes to form alpha or beta glucopyranose.
Question 3: Which disaccharide is composed of glucose and fructose joined by an alpha(1→2) glycosidic bond?
- Lactose
- Maltose
- Sucrose (Correct answer)
- Cellobiose
Correct answer: Sucrose
Sucrose (table sugar) consists of glucose and fructose linked by an unusual alpha(1→2) glycosidic bond involving both anomeric carbons, making it a non-reducing sugar.
Question 4: Glycogen is the storage polysaccharide in animals. Its branching involves which type of linkage?
- Beta(1→4) linkages only
- Alpha(1→4) in chains with alpha(1→6) at branch points (Correct answer)
- Alpha(1→2) linkages throughout
- Beta(1→3) linkages at branch points
Correct answer: Alpha(1→4) in chains with alpha(1→6) at branch points
Glycogen has linear alpha(1→4)-linked glucose chains with alpha(1→6) branch points approximately every 8–12 residues, allowing rapid glucose release from multiple ends simultaneously.
Question 5: The enzyme lactase cleaves lactose into which two monosaccharides?
- Glucose + glucose
- Glucose + galactose (Correct answer)
- Glucose + fructose
- Galactose + fructose
Correct answer: Glucose + galactose
Lactase (beta-galactosidase) hydrolyzes the beta(1→4) glycosidic bond of lactose to release glucose and galactose, which are absorbed in the small intestine.
Question 6: Which reaction does hexokinase catalyze in the first step of glycolysis?
- Glucose → glucose-6-phosphate (using ATP) (Correct answer)
- Glucose-6-phosphate → fructose-6-phosphate
- Fructose-6-phosphate → fructose-1,6-bisphosphate
- Glucose → glucose-1-phosphate
Correct answer: Glucose → glucose-6-phosphate (using ATP)
Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate using ATP, trapping glucose in the cell and committing it to metabolism.
Biochemistry Carbohydrate Chemistry and Metabolism 1
Which monosaccharide is the primary fuel for the brain under normal conditions?