Protein refolding is carried out by?
Where does oxidative deamination primarily occur in the human body?
Which of the following is a plasma protein involved in blood clotting?
Which carbohydrate is primarily metabolized by Aldolase-B?
Which of the following statements BEST describes the net ATP production in glycolysis?
What cofactor is required for the proper functioning of glucose-6-phosphate dehydrogenase?
Which of the following substances does not inhibit glycolysis?
Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?
Mutation in GLUT-2 causes which syndrome?
Which of the following is monoenoic acid ?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 71: Protein refolding is carried out by?
- A. Valine
- B. Threonine
- C. Chaperone (Correct Answer)
- D. Aspartate
Explanation: ***Chaperone*** - **Chaperone proteins** assist in the proper folding of other proteins, particularly during stress conditions like heat shock, by preventing **aggregation** and promoting correct conformation. - They do not become part of the final functional protein but transiently bind during the folding process, thus facilitating **protein refolding** and assembly. *Valine* - **Valine** is an **essential amino acid** and a building block for proteins, but it does not play a direct role in protein refolding. - It contributes to the **hydrophobic core** of proteins due to its non-polar side chain, influencing protein structure but not managing the folding process. *Threonine* - **Threonine** is an **essential amino acid** with a polar side chain, often involved in **glycosylation** and phosphorylation, but not in the complex process of protein refolding. - Its hydroxyl group can participate in **hydrogen bonding**, influencing protein stability and interactions, but not acting as a folding catalyst. *Aspartate* - **Aspartate** is a **non-essential acidic amino acid** that can be involved in various metabolic pathways and is a component of proteins. - Its acidic side chain can form **salt bridges** and hydrogen bonds, contributing to the protein's overall charge and structure, but it does not actively oversee protein refolding.
Question 72: Where does oxidative deamination primarily occur in the human body?
- A. Cytoplasm of all cells
- B. Mitochondria of all cells
- C. Cytoplasm of liver cells
- D. Mitochondria of liver cells (Correct Answer)
Explanation: ***Mitochondria of liver cells*** - **Oxidative deamination**, particularly of glutamate, is a central process in **amino acid catabolism** and occurs predominantly in the **mitochondria of liver cells**. - This process is crucial for removing the **amino group (NH3)** from amino acids, forming ammonia, which is then detoxified into urea. *Cytoplasm of all cells* - While cells have cytoplasmic metabolic pathways, the primary enzyme for oxidative deamination, **glutamate dehydrogenase**, is located in the mitochondria. - The cytoplasm primarily handles glycolysis and various synthetic pathways, but not the bulk of oxidative deamination. *Mitochondria of all cells* - Although mitochondria are the site of oxidative metabolism in most cells, the **liver** is the main organ responsible for processing exogenous amino acids and their subsequent comprehensive deamination. - Other cells perform some amino acid metabolism, but not the large-scale oxidative deamination seen in the liver. *Cytoplasm of liver cells* - The cytoplasm of liver cells is involved in various metabolic processes, including gluconeogenesis and fatty acid synthesis. - However, the key enzymes for oxidative deamination are specifically compartmentalized within the **mitochondria** of these cells, not the cytoplasm.
Question 73: Which of the following is a plasma protein involved in blood clotting?
- A. Fibrinogen (Correct Answer)
- B. Lactate dehydrogenase (LDH)
- C. Aspartate aminotransferase (SGOT)
- D. Alanine aminotransferase (SGPT)
Explanation: ***Fibrinogen*** - **Fibrinogen** is a crucial plasma protein that is converted into **fibrin** during the coagulation cascade. - **Fibrin** then forms a meshwork, which is the structural basis of a **blood clot**. *Lactate dehydrogenase (LDH)* - **LDH** is an enzyme found in many tissues throughout the body and is involved in **cellular metabolism**, specifically the conversion of pyruvate to lactate. - Elevated levels of **LDH** can indicate tissue damage or disease but are not directly involved in blood clotting. *Aspartate aminotransferase (SGOT)* - **SGOT** (now commonly referred to as **AST**) is an enzyme primarily found in the **liver, heart, skeletal muscle, kidneys, brain, and red blood cells**. - High levels of **AST** are often indicative of **liver damage** or other organ injury, but it does not play a direct role in blood coagulation. *Alanine aminotransferase (SGPT)* - **SGPT** (now commonly referred to as **ALT**) is an enzyme predominantly found in the **liver**. - Elevated **ALT** levels are a sensitive marker for **liver cell damage** but are not involved in the blood clotting process.
Question 74: Which carbohydrate is primarily metabolized by Aldolase-B?
- A. Galactose
- B. Fructose (Correct Answer)
- C. Sucrose
- D. None of the options
Explanation: ***Fructose*** - **Aldolase B** is a key enzyme in the liver responsible for the metabolism of **fructose**, specifically cleaving **fructose-1-phosphate** into **dihydroxyacetone phosphate** and **glyceraldehyde**. - A deficiency in **Aldolase B** leads to **hereditary fructose intolerance**, causing an accumulation of **fructose-1-phosphate** after fructose ingestion. *Galactose* - **Galactose** is primarily metabolized by enzymes in the **Leloir pathway**, including **galactokinase** and **galactose-1-phosphate uridylyltransferase**. - **Aldolase B** plays no significant role in the metabolism of galactose. *Sucrose* - **Sucrose** is a disaccharide composed of **glucose** and **fructose**. - It is first broken down by **sucrase** in the small intestine into its constituent monosaccharides before they are metabolized further. *None of the options* - This option is incorrect because **fructose** is indeed a carbohydrate primarily metabolized by Aldolase-B. - The enzyme's specific role in fructose metabolism is well-established.
Question 75: Which of the following statements BEST describes the net ATP production in glycolysis?
- A. Glycolysis produces 2 molecules of pyruvate
- B. Glycolysis produces a net gain of 2 ATP per glucose molecule (Correct Answer)
- C. Hexokinase consumes ATP during glycolysis
- D. Aldolase catalyzes the conversion of fructose-1,6-bisphosphate into two three-carbon molecules
Explanation: ***Glycolysis produces a net gain of 2 ATP per glucose molecule*** - In the initial "investment" phase of glycolysis, **2 ATP molecules are consumed** to phosphorylate glucose. - In the subsequent "payoff" phase, **4 ATP molecules are produced** through substrate-level phosphorylation, resulting in a net gain of 2 ATP. *Glycolysis produces 2 molecules of pyruvate* - While glycolysis does produce **2 molecules of pyruvate** from one glucose molecule, this statement describes the end product of the pathway, not the net ATP production. - Pyruvate is a crucial product that can be further metabolized in aerobic or anaerobic conditions, but it does not directly represent the energy yield in terms of ATP. *Hexokinase consumes ATP during glycolysis* - **Hexokinase** is indeed the enzyme that catalyzes the first ATP-consuming step in glycolysis, phosphorylating glucose to glucose-6-phosphate. - However, this statement describes only one aspect of ATP utilization within the pathway and does not account for the total ATP produced or the overall net gain. *Aldolase catalyzes the conversion of fructose-1,6-bisphosphate into two three-carbon molecules* - **Aldolase** is a key enzyme in glycolysis responsible for cleaving **fructose-1,6-bisphosphate** into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. - This step is part of the preparatory phase of glycolysis but does not directly describe the net ATP production.
Question 76: What cofactor is required for the proper functioning of glucose-6-phosphate dehydrogenase?
- A. NAD
- B. NADP (Correct Answer)
- C. FAD
- D. FMN
Explanation: ***NADP*** - **NADP+** (nicotinamide adenine dinucleotide phosphate) acts as the **electron acceptor** in the **glucose-6-phosphate dehydrogenase (G6PD)** reaction, becoming **NADPH**. - **NADPH** is crucial for maintaining the **redox balance** in cells, particularly in red blood cells, by reducing **oxidative stress**. *NAD* - **NAD+** (nicotinamide adenine dinucleotide) is a primary cofactor for many **dehydrogenase reactions** in catabolic pathways like **glycolysis** and the **Krebs cycle**. - It primarily functions as an electron acceptor in pathways that generate **ATP**, distinct from the role of **NADPH** in reductive biosynthesis and antioxidant defense. *FAD* - **FAD** (flavin adenine dinucleotide) is a coenzyme derived from **riboflavin (vitamin B2)** that is involved in various redox reactions, often in the form of **flavoproteins**. - Enzymes like **succinate dehydrogenase** in the electron transport chain utilize **FAD** as an electron acceptor, which is not the case for G6PD. *FMN* - **FMN** (flavin mononucleotide) is another coenzyme derived from **riboflavin**, structurally similar to FAD but lacking the additional adenosine monophosphate. - It participates in electron transfer reactions, particularly within **complex I** of the **electron transport chain**, but is not a cofactor for G6PD.
Question 77: Which of the following substances does not inhibit glycolysis?
- A. Fluoride
- B. Arsenite
- C. Iodoacetate
- D. Fluoroacetate (Correct Answer)
Explanation: ***Fluoroacetate*** - **Fluoroacetate** is not a direct inhibitor of glycolysis. Instead, it is metabolized to **fluorocitrate**, which then acts as an inhibitor of **aconitase** in the **Krebs cycle (TCA cycle)**, thereby affecting cellular respiration at a later stage. - Its primary role in metabolic inhibition is within the **mitochondria**, impacting energy production via the TCA cycle rather than the glycolytic pathway. *Fluoride* - **Fluoride** is a known inhibitor of **enolase**, an enzyme in the penultimate step of glycolysis. - It forms a complex with **magnesium** and **phosphate** to block the active site of enolase, preventing the conversion of 2-phosphoglycerate to phosphoenolpyruvate. *Arsenite* - **Arsenite** inhibits glycolysis by targeting enzymes containing **sulfhydryl (–SH) groups**, particularly **glyceraldehyde-3-phosphate dehydrogenase (GAPDH)**, a critical enzyme in the glycolytic pathway. - It also inhibits the **pyruvate dehydrogenase complex** (linking glycolysis to the TCA cycle) and TCA cycle enzymes like **α-ketoglutarate dehydrogenase**, thereby affecting multiple stages of cellular respiration. *Iodoacetate* - **Iodoacetate** is a potent inhibitor of the enzyme **glyceraldehyde-3-phosphate dehydrogenase (GAPDH)**. - It specifically alkylates the **cysteine residue** at the active site of GAPDH, preventing the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, thereby blocking glycolysis.
Question 78: Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?
- A. Liver
- B. Kidney
- C. Adipose tissue
- D. Muscle (Correct Answer)
Explanation: ***Muscle*** - Muscle tissue lacks the enzyme **glucose-6-phosphatase**, which is essential for hydrolyzing glucose 6-phosphate back to **free glucose**. - Therefore, glucose 6-phosphate in muscle is primarily used for **glycolysis** (energy production) or stored as glycogen for local use. *Liver* - The liver contains **glucose-6-phosphatase**, allowing it to convert **glucose 6-phosphate** to **free glucose**. - This capability is crucial for maintaining **blood glucose homeostasis** and releasing glucose into circulation. *Adipose tissue* - Adipose tissue, like muscle, **lacks glucose-6-phosphatase** and cannot convert glucose 6-phosphate back to free glucose. - Glucose 6-phosphate in adipose tissue is primarily channeled into **fatty acid synthesis** and storage. *Kidney* - The kidney, particularly the renal cortex, possesses **glucose-6-phosphatase** and can convert glucose 6-phosphate to **free glucose**. - This contributes to **gluconeogenesis** and release of glucose into the blood, especially during fasting.
Question 79: Mutation in GLUT-2 causes which syndrome?
- A. Dandy walker syndrome
- B. Beckwith-Wiedemann syndrome
- C. Menke's disease
- D. Fanconi-Bickel syndrome (Correct Answer)
Explanation: ***Fanconi-Bickel syndrome*** - This syndrome is caused by a **mutation in the GLUT-2 gene**, leading to dysfunctional glucose transport in the liver, kidneys, and intestines. - Key features include **hepatorenal glycogen accumulation**, **renal tubulopathy** (Fanconi syndrome), and **impaired glucose and galactose utilization**. *Dandy-Walker syndrome* - This is a **congenital brain malformation** involving the cerebellum and fourth ventricle. - It is often associated with hydrocephalus, but not directly linked to glucose transporter defects. *Beckwith-Wiedemann syndrome* - This is an **overgrowth disorder** characterized by a high risk of childhood cancer and congenital anomalies. - It is primarily caused by genetic abnormalities on **chromosome 11p15.5** and is unrelated to GLUT-2 mutations. *Menke's disease* - This is a rare X-linked recessive disorder of **copper metabolism**, leading to severe neurological degeneration. - It results from mutations in the **ATP7A gene**, which encodes a copper-transporting ATPase.
Question 80: Which of the following is monoenoic acid ?
- A. Linoleic acid
- B. Oleic acid (Correct Answer)
- C. Linolenic acid
- D. Arachidonic acid
Explanation: ***Oleic acid*** - **Oleic acid** is a **monounsaturated fatty acid** (MUFA), meaning it has **one double bond** in its hydrocarbon chain. - Its presence in many natural fats and oils makes it a significant component of the human diet. *Arachidonic acid* - **Arachidonic acid** is a **polyunsaturated fatty acid** (PUFA) containing **four double bonds**. - It is a precursor for **eicosanoids**, including prostaglandins and leukotrienes, involved in inflammation and other physiological processes. *Linoleic acid* - **Linoleic acid** is an **essential omega-6 polyunsaturated fatty acid** with **two double bonds**. - It is crucial for human health and serves as a precursor for other fatty acids like arachidonic acid. *Linolenic acid* - **Linolenic acid** refers to two essential fatty acids: **alpha-linolenic acid (ALA)**, an omega-3 fatty acid with **three double bonds**, and **gamma-linolenic acid (GLA)**, an omega-6 fatty acid also with three double bonds. - Both are **polyunsaturated fatty acids** with multiple double bonds.