Carbohydrates
Which of the following carbohydrates does NOT undergo glycolysis?
A
Glucose
B
Mannose
C
Cellulose
D
Galactose
Correct Answer:
C. Cellulose
Cellulose is a β-1,4-linked glucose polymer that humans cannot digest due to lack of cellulase enzyme. It cannot enter glycolysis.
The optical rotation of freshly prepared glucose solution gradually decreases and reaches equilibrium. This phenomenon is called:
A
Mutarotation
B
Epimerization
C
Isomerization
D
Racemization
Correct Answer:
A. Mutarotation
Mutarotation is the spontaneous interconversion between α and β anomers of glucose at the anomeric carbon until equilibrium is reached.
Which enzyme catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate?
A
Phosphofructokinase
B
Phosphoglucose isomerase
C
Hexokinase
D
Aldolase
Correct Answer:
B. Phosphoglucose isomerase
Phosphoglucose isomerase catalyzes the interconversion of glucose-6-phosphate and fructose-6-phosphate in glycolysis.
The disaccharide formed by α-glucose and β-fructose joined by α-1,2-glycosidic bond is:
A
Lactose
B
Maltose
C
Sucrose
D
Trehalose
Correct Answer:
C. Sucrose
Sucrose is composed of glucose and fructose linked by α-1,2-glycosidic bond. Maltose has α-1,4 bond between two glucose molecules.
Which of the following carbohydrates is a ketohexose?
A
Fructose
B
Glucose
C
Galactose
D
Ribose
Correct Answer:
A. Fructose
Fructose is a ketohexose (6-carbon ketone sugar), while glucose, galactose are aldohexoses, and ribose is a pentose.
Which of the following is a reducing sugar?
A
Sucrose
B
Trehalose
C
Maltose
D
Lactose is incorrect
Correct Answer:
C. Maltose
Maltose is a reducing sugar because it has a free anomeric carbon. Sucrose and trehalose are non-reducing sugars as both anomeric carbons are involved in glycosidic bonds.
What is the net yield of ATP from the anaerobic metabolism of one molecule of glucose?
A
2 ATP
B
4 ATP
C
30 ATP
D
38 ATP
Anaerobic glycolysis produces 4 ATP molecules but consumes 2 ATP, resulting in a net gain of 2 ATP per glucose molecule.
Which enzyme is the rate-limiting step of glycolysis and is inhibited by ATP and citrate?
A
Hexokinase
B
Phosphofructokinase-1
C
Pyruvate kinase
D
Enolase
Correct Answer:
B. Phosphofructokinase-1
Phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate and is subject to allosteric inhibition by ATP and citrate.
In glycolysis, the conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by which enzyme?
A
Hexokinase
B
Phosphoglucose isomerase
C
Phosphofructokinase
D
Aldolase
Correct Answer:
B. Phosphoglucose isomerase
Phosphoglucose isomerase catalyzes the isomerization of glucose-6-phosphate to fructose-6-phosphate in the second step of glycolysis.
Which of the following carbohydrates is classified as a pentose sugar?
A
Ribose
B
Glucose
C
Galactose
D
Fructose
Correct Answer:
A. Ribose
Ribose is a 5-carbon (pentose) sugar, while glucose, galactose, and fructose are hexoses (6-carbon sugars).
