Biochemistry sits at the point where chemistry stops being abstract and starts describing living systems. Practice covers carbohydrates, proteins and amino acids, lipids, nucleic acids, enzymes and enzyme kinetics, metabolic pathways, and vitamins and coenzymes. Pathway questions include the regulation step in the explanation, because that is usually what the question is really testing rather than the sequence itself.
Which of the following is a pentose sugar found in RNA?
Answer: A
Ribose is a pentose sugar (5-carbon sugar) that is a component of RNA. Deoxyribose is found in DNA, while glucose and fructose are hexose sugars.
Q.2Easy
Glycogen is primarily stored in which of the following tissues in humans?
Answer: B
Glycogen, the storage polysaccharide in animals, is primarily stored in the liver (100-120g) and skeletal muscles (400-500g). The liver glycogen maintains blood glucose, while muscle glycogen is used locally.
Q.3Easy
What is the glycosidic linkage present in maltose?
Answer: A
Maltose consists of two glucose units linked by an α(1→4) glycosidic bond. This is a reducing disaccharide formed during starch digestion.
Q.4Easy
Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate?
Answer: B
Phosphoglucose isomerase (PGI) catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis, step 2.
Q.5Easy
Sucrose is composed of which two monosaccharides?
Answer: B
Sucrose (table sugar) is a disaccharide composed of one glucose and one fructose unit linked by an α(1→2) glycosidic bond. It is a non-reducing sugar.
Q.6Easy
Which carbohydrate classification includes both monosaccharides and oligosaccharides?
Answer: B
Simple carbohydrates include monosaccharides (glucose, fructose, galactose) and oligosaccharides (2-10 units like sucrose, maltose, lactose). Complex carbohydrates are polysaccharides with >10 units (starch, glycogen, cellulose).
Q.7Easy
Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis?
Answer: A
Phosphoglucose isomerase catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, the second step of glycolysis.
Q.8Easy
What is the maximum number of ATP molecules generated from complete oxidation of one glucose molecule under aerobic conditions?
Answer: A
Complete oxidation of glucose yields approximately 30-32 ATP molecules when accounting for the cost of transporting NADH across the mitochondrial membrane (P/O ratio of 2.5 for NADH and 1.5 for FADH2).
Q.9Easy
Which carbohydrate is a non-reducing sugar due to the glycosidic linkage between anomeric carbons of both monosaccharides?
Answer: B
Sucrose (α-glucose + β-fructose) is a non-reducing sugar because both anomeric carbons are involved in the 1,2-glycosidic linkage, making it unable to reduce Benedict's reagent.
Q.10Easy
In fructose metabolism, fructose is primarily phosphorylated by which enzyme in the liver?
Answer: B
Fructokinase phosphorylates fructose to fructose-1-phosphate in the liver. This bypasses the rate-limiting phosphofructokinase step, making fructose metabolism less regulated.
Q.11Easy
Which of the following carbohydrates is a heptose?
Answer: B
Sedoheptulose is a seven-carbon ketose (heptose) that participates in the non-oxidative phase of the pentose phosphate pathway.
Q.12Easy
In glycogen synthesis, which enzyme transfers glucose from UDP-glucose to the growing glycogen chain?
Answer: B
Glycogen synthase catalyzes the transfer of glucose from UDP-glucose to the C4-OH group of the terminal glucose in glycogen, forming α-1,4-glycosidic bonds.
Q.13Easy
Which monosaccharide is the C2 epimer of glucose?
Answer: B
Mannose differs from glucose only at the C2 position (the configuration of the -OH group and -H). Therefore, mannose is the C2 epimer of glucose.
Q.14Easy
Which of the following is a ketohexose that is a structural isomer of glucose?
Answer: A
Fructose is a ketohexose (6-carbon ketone sugar) with the molecular formula C₆H₁₂O₆, making it a structural isomer of glucose. Galactose and mannose are aldohexoses (epimers of glucose), while ribose is a pentose.
Q.15Easy
Which disaccharide is formed by α-1,4-glycosidic linkage between glucose molecules?
Answer: C
Maltose consists of two glucose units linked by an α-1,4-glycosidic bond. Sucrose contains glucose and fructose, lactose contains glucose and galactose, and trehalose has an α-1,1-glycosidic linkage.
Q.16Easy
Which carbohydrate is a non-reducing sugar that cannot undergo mutarotation?
Answer: B
Sucrose is a non-reducing disaccharide formed by α-1,2-glycosidic linkage between C1 of glucose and C2 of fructose, blocking both anomeric carbons. It cannot mutarotate or act as a reducing sugar. Other options are reducing sugars with free anomeric carbons.
Q.17Easy
Which of the following carbohydrates is classified as a pentose sugar?
Answer: A
Ribose is a 5-carbon (pentose) sugar, while glucose, galactose, and fructose are hexoses (6-carbon sugars).
Q.18Easy
In glycolysis, the conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by which enzyme?
Answer: B
Phosphoglucose isomerase catalyzes the isomerization of glucose-6-phosphate to fructose-6-phosphate in the second step of glycolysis.
Q.19Easy
Which enzyme is the rate-limiting step of glycolysis and is inhibited by ATP and citrate?
Answer: B
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.
Q.20Easy
What is the net yield of ATP from the anaerobic metabolism of one molecule of glucose?
Answer: A
Anaerobic glycolysis produces 4 ATP molecules but consumes 2 ATP, resulting in a net gain of 2 ATP per glucose molecule.
