Biochemistry MCQs (Set 1): 20 Questions with Answers & Detailed Explanations Boost your biology knowledge with this Biochemistry MCQs (Set 1): 20 Questions with Answers & Detailed Explanations quiz. This interactive quiz is specially designed for students, competitive exam aspirants, and medical science learners who want to strengthen their understanding of core biochemistry concepts. 1 / 20 1) What is a peptide bond? A bond between two fatty acids A bond between two amino acids A bond between a sugar and a phosphate group A bond between two nucleotides Explanation:A peptide bond is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another amino acid, resulting in the formation of proteins. 2 / 20 2) Which of the following best explains the concept of the Michaelis-Menten theory in enzyme action? Enzymes permanently bind with substrates to form stable compounds Enzymes convert directly into products without interacting with substrates Enzymes temporarily form a complex with substrates before releasing products Enzymes are consumed completely during the chemical reaction Explanation:The Michaelis-Menten theory describes how an enzyme first binds with a substrate to form an enzyme-substrate complex. This complex is short-lived and quickly breaks down to release the product while the enzyme remains unchanged. This allows the enzyme to be reused in further reactions. 3 / 20 3) What effect do enzymes have on the activation energy of a chemical reaction? They increase the activation energy to speed up reactions They lower the activation energy required for the reaction They completely eliminate the need for activation energy They do not affect activation energy but increase temperature Explanation:Enzymes act as biological catalysts that reduce the activation energy needed for a reaction to occur. By lowering this energy barrier, enzymes make reactions happen faster and more efficiently. However, they do not eliminate activation energy completely-they just make it easier to achieve. 4 / 20 4) Which type of sugar is primarily present in milk? Sucrose Sucrose Lactose Fructose Explanation:Lactose is the main sugar found in milk and is often called “milk sugar.” It is a disaccharide made of glucose and galactose. Lactose is digested in the body by the enzyme lactase, mainly in the small intestine. 5 / 20 5) Which of the following food sources is rich in polyunsaturated fatty acids (PUFA)? Butter and ghee Vegetable oils like sunflower and groundnut oil Red meat and animal fat Red meat and animal fat Polyunsaturated fatty acids (PUFAs) are healthy fats mainly found in plant-based oils. Oils such as sunflower and groundnut oil contain a high amount of PUFA, which helps in maintaining heart health. In contrast, animal fats are usually richer in saturated fats rather than PUFAs. 6 / 20 6) In a normal resting condition, which tissue utilizes the majority of glucose in the human body? Skeletal muscles Liver Brain Adipose tissue Explanation:During the resting state, the brain is the primary consumer of glucose as it relies almost entirely on glucose for energy. Unlike other tissues, it cannot store glucose and needs a constant supply from the blood. This makes glucose essential for proper brain function. 7 / 20 7) Under which condition is pyruvate primarily formed during glucose metabolism? Anaerobic condition without oxygen Aerobic condition in the presence of oxygen During protein metabolism only In the absence of enzymes Explanation:Pyruvate is produced at the end of glycolysis, which occurs in both aerobic and anaerobic conditions. However, in aerobic conditions, pyruvate is further utilized in the mitochondria for energy production. Oxygen presence ensures efficient conversion of glucose to pyruvate and further energy release. 8 / 20 8) Under which condition is lactate produced in the body during metabolism? In the presence of excess oxygen During aerobic respiration When oxygen supply is insufficient During fat metabolism only Explanation:Lactate is formed when there is a lack of oxygen in the tissues, a condition known as anaerobic metabolism. In this situation, pyruvate is converted into lactate to allow glycolysis to continue producing energy. This commonly occurs during intense exercise when oxygen demand exceeds supply. 9 / 20 9) During glycolysis, in which step is NAD⁺ reduced to NADH? Conversion of glucose to glucose-6-phosphate Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate Conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate Conversion of phosphoenolpyruvate to pyruvate Explanation:In glycolysis, NAD⁺ is reduced to NADH during the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase. In this step, glyceraldehyde-3-phosphate is oxidized, and electrons are transferred to NAD⁺, forming NADH. This is an important energy-yielding step in the pathway. 10 / 20 10) What is the main function of gluconeogenesis in the body? Breakdown of glucose into pyruvate Formation of glycogen from glucose Production of glucose from non-carbohydrate sources Conversion of glucose into fatty acids Explanation:Gluconeogenesis is a metabolic process in which glucose is synthesized from non-carbohydrate sources such as amino acids, lactate, and glycerol. It mainly occurs in the liver and helps maintain blood glucose levels during fasting or starvation. 11 / 20 11) Which hormone plays a key role in inhibiting gluconeogenesis in the body? Glucagon Insulin Cortisol Adrenaline Explanation:Insulin inhibits gluconeogenesis by reducing the production of glucose from non-carbohydrate sources in the liver. It promotes glucose uptake and storage, thereby lowering blood glucose levels. In contrast, hormones like glucagon and cortisol stimulate gluconeogenesis. 12 / 20 12) Which of the following hormones stimulates gluconeogenesis in the body? Insulin and estrogen Thyroxine and insulin Glucagon and glucocorticoids Progesterone and prolactin Explanation:Glucagon and glucocorticoids (like cortisol) promote gluconeogenesis, especially during fasting or stress. These hormones increase the production of glucose from non-carbohydrate sources in the liver. In contrast, insulin inhibits this process to lower blood glucose levels. 13 / 20 13) What is the primary function of the HMP shunt pathway (pentose phosphate pathway) in cells? Production of ATP for cellular energy Generation of NADPH for biosynthetic reactions Breakdown of fatty acids into acetyl-CoA Conversion of glucose into glycogen Explanation:The HMP shunt pathway mainly produces NADPH, which is essential for reductive biosynthesis and protection against oxidative stress. NADPH is used in processes like fatty acid synthesis and maintaining reduced glutathione. It is not primarily involved in ATP production. 14 / 20 14) Which type of cholesterol is commonly referred to as “bad cholesterol” due to its role in plaque formation in arteries? HDL cholesterol Triglycerides LDL cholesterol Phospholipids Explanation:LDL (Low-Density Lipoprotein) cholesterol is called “bad cholesterol” because it can deposit cholesterol in the walls of arteries, leading to plaque formation and increasing the risk of heart disease. In contrast, HDL helps remove excess cholesterol from the bloodstream. 15 / 20 15) Which type of cholesterol is known as “good cholesterol” because it helps remove excess cholesterol from the bloodstream? HDL cholesterol Triglycerides LDL cholesterol Phospholipids Explanation:HDL (High-Density Lipoprotein) cholesterol is called “good cholesterol” because it carries excess cholesterol from tissues back to the liver for removal. This process helps prevent plaque buildup in arteries and reduces the risk of cardiovascular diseases. 16 / 20 16) Which statement correctly describes GABA in the human nervous system? It is an excitatory neurotransmitter formed from glycine It is an inhibitory neurotransmitter produced from glutamic acid It is a hormone secreted by the endocrine glands It is a neurotransmitter synthesized from dopamine Explanation:GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the central nervous system. It is formed by the decarboxylation of glutamic acid. GABA reduces neuronal excitability, helping to maintain balance and prevent overactivity in the brain. 17 / 20 17) Which enzyme acts as the rate-limiting step in the synthesis of heme? ALA synthase Ferrochelatase Porphobilinogen deaminase Uroporphyrinogen decarboxylase Explanation:ALA synthase is the rate-limiting enzyme in heme synthesis and controls the overall speed of the pathway. It catalyzes the first step, forming δ-aminolevulinic acid (ALA) from glycine and succinyl-CoA. Regulation of this enzyme ensures proper heme production in the body. 18 / 20 18) Deficiency of which enzyme is inherited as an X-linked disorder? Hexokinase Glucose-6-phosphate dehydrogenase Lactate dehydrogenase Pyruvate kinase Explanation:Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked genetic disorder. It affects red blood cells, making them more vulnerable to oxidative damage. This can lead to hemolytic anemia, especially under stress conditions like infections or certain drugs. 19 / 20 19) Which of the following coenzymes are derived from Niacin and play a key role in oxidation-reduction reactions? FAD and FMN NAD⁺ and NADP⁺ Coenzyme A and biotin TPP and pyridoxal phosphate Explanation:Niacin (vitamin B₃) is the precursor of the coenzymes NAD⁺ and NADP⁺. These molecules are essential for redox reactions in metabolism, acting as electron carriers. They play a vital role in energy production and various biochemical pathways. 20 / 20 20) In the mitochondrial respiratory chain, which complex is known as Complex V? Cytochrome c oxidase NADH dehydrogenase ATP synthase Succinate dehydrogenase Explanation:Complex V of the respiratory chain is ATP synthase. It uses the proton gradient generated by earlier complexes to produce ATP from ADP and inorganic phosphate. This process is called oxidative phosphorylation and is essential for cellular energy production. Your score isThe average score is 78% 0% Restart quiz
