Mutation in GLUT-2 causes which syndrome?
Which of the following is monoenoic acid ?
Which of the following fatty acids has the maximum number of carbon atoms?
Chylomicron remnants are associated with ?
Which of the following statements is true regarding medium chain fatty acids?
In which condition does serum appear milky white?
Which of the following is a non-essential amino acid?
Hydrolysis occurs at which step of urea cycle ?
Which technique is used for the separation of proteins based on their mass?
Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 111: 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 112: 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.
Question 113: Which of the following fatty acids has the maximum number of carbon atoms?
- A. Oleic acid
- B. Linolenic acid
- C. Arachidonic acid
- D. Cervonic acid (Correct Answer)
Explanation: **Cervonic acid** - **Cervonic acid**, also known as **docosahexaenoic acid (DHA)**, is a long-chain omega-3 fatty acid with **22 carbon atoms** and 6 double bonds (22:6). - It is a primary structural component of the brain and retina and is the longest fatty acid among the options provided. *Oleic acid* - **Oleic acid** is a monounsaturated fatty acid with **18 carbon atoms** and one double bond (18:1). - It is a common fatty acid found in many animal fats and vegetable oils, but it has fewer carbon atoms than cervonic acid. *Linolenic acid* - **Linolenic acid** refers to two essential fatty acids: alpha-linolenic acid (ALA) and gamma-linolenic acid (GLA). Both have **18 carbon atoms**. - Alpha-linolenic acid (ALA) is an omega-3 fatty acid with 3 double bonds (18:3), while gamma-linolenic acid (GLA) is an omega-6 fatty acid with 3 double bonds (18:3), neither of which has more carbon atoms than cervonic acid. *Arachidonic acid* - **Arachidonic acid** is an omega-6 fatty acid with **20 carbon atoms** and four double bonds (20:4). - It is a precursor to eicosanoids and is longer than oleic and linolenic acids but shorter than cervonic acid.
Question 114: Chylomicron remnants are associated with ?
- A. Apo-C
- B. Apo-A
- C. Apo-E (Correct Answer)
- D. Apo-B100
Explanation: ***Apo-E*** - **Apolipoprotein E (Apo-E)** is a crucial apolipoprotein on the surface of chylomicron remnants, acting as a **ligand for the LDL receptor-related protein 1 (LRP1)** in the liver. - This binding facilitates the **hepatic uptake and clearance** of chylomicron remnants from circulation. *Apo-A* - **Apo-AI** is the primary apolipoprotein of **HDL** and plays a key role in reverse cholesterol transport by activating **lecithin-cholesterol acyltransferase (LCAT)**. - While chylomicrons *acquire* some Apo-AI from HDL, it is not the primary apolipoprotein defining their remnants' hepatic clearance. *Apo-C* - **Apo-CII** is a vital activator of **lipoprotein lipase (LPL)**, which metabolizes triglycerides in chylomicrons and VLDL. - **Apo-CIII** inhibits LPL and hinders receptor-mediated uptake, but **Apo-E** is the key for remnant recognition and uptake, not Apo-C in general. *Apo-B100* - **Apo-B100** is the main structural apolipoprotein of **LDL** and **VLDL**, serving as the ligand for the LDL receptor, mediating their hepatic uptake. - While chylomicrons have **Apo-B48**, which is a truncated form of Apo-B100, Apo-B100 itself is not found on chylomicron remnants.
Question 115: Which of the following statements is true regarding medium chain fatty acids?
- A. All of the options are true (Correct Answer)
- B. Do not require pancreatic lipase for digestion
- C. Absorb directly into portal circulation
- D. Are less likely to be deposited in adipose tissue compared to long-chain fatty acids
Explanation: ***All of the options are true*** - This option is correct because medium-chain fatty acids (MCFAs) possess unique metabolic properties that differentiate them from long-chain fatty acids (LCFAs), making all listed statements accurate. - Their shorter chain length allows for distinct digestion, absorption, and metabolic fates, which are beneficial in various clinical contexts. *Do not require pancreatic lipase for digestion* - MCFAs have **shorter carbon chains** (typically 6-12 carbons) and are more hydrophilic than LCFAs. - This property allows them to be digested by **lingual and gastric lipases** to a greater extent, reducing the reliance on pancreatic lipase. *Absorb directly into portal circulation* - Unlike LCFAs, which are re-esterified into triglycerides, packaged into **chylomicrons**, and absorbed into the lymphatic system, MCFAs are absorbed directly into the **portal vein**. - This bypasses the lymphatic system and directly transports them to the liver, making them a rapid energy source. *Are less likely to be deposited in adipose tissue compared to long-chain fatty acids* - MCFAs are **rapidly oxidized** in the liver for energy via beta-oxidation and are less likely to be stored as triglycerides in adipose tissue. - They are also not efficiently utilized for the synthesis of complex lipids or stored fat due to their unique metabolic pathway and preference for oxidation.
Question 116: In which condition does serum appear milky white?
- A. Increased LDL
- B. Increased HDL
- C. Increased VLDL
- D. Increased Chylomicrons (Correct Answer)
Explanation: ***Increased Chylomicrons*** - **Chylomicrons** are the largest lipoprotein particles (75-1200 nm) with the highest **triglyceride content (85-95%)**, giving serum a characteristic **milky white** or "creamy" appearance - This intense milky appearance occurs after **fatty meals** (postprandial lipemia) or in **Type I and V hyperlipidemias** (familial chylomicronemia syndrome) - The **light scattering** by these large particles makes the serum completely opaque, distinguishing it from other lipid abnormalities - Classic clinical finding: **"cream layer" forms on top** when lipemic serum stands overnight in refrigerator *Increased LDL* - Elevated **Low-Density Lipoprotein (LDL)** produces **clear to slightly hazy** serum, never milky white - LDL particles are much smaller (18-25 nm) than chylomicrons and contain primarily **cholesterol**, not triglycerides - High LDL is a cardiovascular risk factor but does not cause visible lipemia *Increased HDL* - **High-Density Lipoprotein (HDL)** elevation results in **clear serum** - HDL particles are the smallest (5-12 nm) and densest lipoproteins - High HDL is protective and causes no turbidity *Increased VLDL* - **Very Low-Density Lipoprotein (VLDL)** elevation can cause **turbid or hazy** serum in severe hypertriglyceridemia, but typically less intensely milky than chylomicrons - VLDL particles are smaller (30-80 nm) than chylomicrons with lower triglyceride content (50-65%) - In Type IV hyperlipidemia (isolated VLDL elevation), serum appears uniformly turbid without cream layer formation - The most dramatic "milky white" appearance is specifically associated with **chylomicronemia**
Question 117: Which of the following is a non-essential amino acid?
- A. Tyrosine (Correct Answer)
- B. Phenylalanine
- C. Lysine
- D. Threonine
Explanation: ***Tyrosine*** - **Tyrosine** is considered a **non-essential amino acid** because the human body can synthesize it from the essential amino acid **phenylalanine**. - This synthesis occurs via the enzyme **phenylalanine hydroxylase**, making its dietary intake not strictly necessary if phenylalanine is available. *Phenylalanine* - **Phenylalanine** is an **essential amino acid**, meaning the human body **cannot synthesize it** and it must be obtained through the diet. - It serves as a precursor for various important molecules, including tyrosine, contributing to neurotransmitter synthesis. *Lysine* - **Lysine** is an **essential amino acid** that the human body **cannot synthesize** and must be acquired from dietary sources. - It plays a crucial role in **protein synthesis**, calcium absorption, and the production of hormones and enzymes. *Threonine* - **Threonine** is another example of an **essential amino acid** that the human body is **unable to produce** on its own. - It is important for the formation of **collagen** and elastin, and contributes to immune function.
Question 118: Hydrolysis occurs at which step of urea cycle ?
- A. Formation of ornithine
- B. Formation of argininosuccinate
- C. Formation of citrulline
- D. Cleavage of arginine (Correct Answer)
Explanation: ***Cleavage of arginine*** - The final step in the urea cycle, where **arginine** is hydrolyzed by the enzyme **arginase** to form **urea** and **ornithine**. - This reaction involves the addition of a **water molecule** across the guanidino group to release urea. *Formation of argininosuccinate* - This step involves the condensation of **citrulline** and **aspartate**, catalyzed by **argininosuccinate synthetase**. - It is an **ATP-dependent** reaction, not a hydrolysis. *Formation of citrulline* - Occurs when **carbamoyl phosphate** condenses with **ornithine**, catalyzed by **ornithine transcarbamylase**. - This reaction involves the removal of a phosphate group, not the addition of water. *Formation of ornithine* - **Ornithine** is a substrate for the formation of citrulline and is also regenerated at the end of the cycle from arginine. - Its formation from arginine is a **hydrolysis** reaction, but simply stating "formation of ornithine" is less specific than "cleavage of arginine," which directly describes the hydrolytic event.
Question 119: Which technique is used for the separation of proteins based on their mass?
- A. Electrophoresis
- B. Salting out
- C. SDS-PAGE (Correct Answer)
- D. Ion exchange chromatography
Explanation: ***Correct Option: SDS-PAGE*** - **SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis)** separates **denatured proteins** almost exclusively by their **molecular mass**. - **SDS** binds to proteins, imparting a uniform negative charge-to-mass ratio, ensuring that separation is primarily based on their size as they migrate through a **polyacrylamide gel**. - This is the gold standard technique for analyzing proteins by molecular weight. *Incorrect Option: Electrophoresis* - This is a general technique that uses an **electric field** to separate molecules based on their **charge** and **size**. - While it can separate proteins, it doesn't exclusively rely on **mass** without additional modifications (like SDS). - Native electrophoresis separates by charge-to-mass ratio, not mass alone. *Incorrect Option: Salting out* - This technique separates proteins based on their **solubility** in high salt concentrations. - Proteins "salt out" or precipitate at different salt concentrations, which is not directly related to their **mass**. - Based on protein surface properties and hydrophobicity. *Incorrect Option: Ion exchange chromatography* - This method separates proteins based on their **net charge** at a particular pH. - Proteins bind to a charged resin and are eluted by changing the **ionic strength** or **pH** of the buffer. - Two types: cation exchange (negative resin) and anion exchange (positive resin).
Question 120: Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?
- A. Tyrosine (Correct Answer)
- B. Alanine
- C. Histidine
- D. Arginine
Explanation: ***Correct Option: Tyrosine*** - Tyrosine contains a **phenol functional group** (aromatic ring with hydroxyl group), giving it **significant UV absorption at 280 nm** (specifically ~274 nm) - Along with **tryptophan** and **phenylalanine**, tyrosine is one of the three aromatic amino acids used for **protein quantification via UV spectroscopy** - The aromatic side chain with conjugated double bonds enables strong UV light absorption *Incorrect Option: Alanine* - Alanine has a **methyl group** as its side chain (non-polar, aliphatic) - **Lacks aromatic rings** or conjugated systems - Does **not absorb UV light** at 280 nm *Incorrect Option: Histidine* - Histidine has an **imidazole ring** (heterocyclic aromatic) in its side chain - While technically aromatic, it has **minimal UV absorption at 280 nm** (weak absorption around 210-230 nm) - **Not used for protein quantification** at 280 nm due to insignificant absorption at this wavelength *Incorrect Option: Arginine* - Arginine contains a **guanidinium group** (highly basic, polar) - **Non-aromatic structure** without conjugated double bonds - Does **not exhibit UV absorption** at wavelengths used for protein analysis