NEET-PG 2012 - Biochemistry Practice Questions

Q: Protein refolding is carried out by?

Chaperone. ***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.

Q: Where does oxidative deamination primarily occur in the human body?

Mitochondria of liver cells. ***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.

Q: Which of the following is a plasma protein involved in blood clotting?

Fibrinogen. ***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.

Q: Which of the following substances does not inhibit glycolysis?

Fluoroacetate. ***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.

Q: Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?

Muscle. ***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.

Q: Mutation in GLUT-2 causes which syndrome?

Fanconi-Bickel syndrome. ***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.

Q: Which of the following is monoenoic acid ?

Oleic acid. ***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.

Q: Which of the following fatty acids has the maximum number of carbon atoms?

Cervonic acid. **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.

Q: Chylomicron remnants are associated with ?

Apo-E. ***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 1

Protein refolding is carried out by?

Accepted Answer

Chaperone

Answer

Valine

Answer

Threonine

Answer

Aspartate

Question 2

Where does oxidative deamination primarily occur in the human body?

Accepted Answer

Mitochondria of liver cells

Answer

Cytoplasm of all cells

Answer

Mitochondria of all cells

Answer

Cytoplasm of liver cells

Question 3

Which of the following is a plasma protein involved in blood clotting?

Accepted Answer

Fibrinogen

Answer

Lactate dehydrogenase (LDH)

Answer

Aspartate aminotransferase (SGOT)

Answer

Alanine aminotransferase (SGPT)

Question 4

Which of the following statements BEST describes the net ATP production in glycolysis?

Accepted Answer

Glycolysis produces a net gain of 2 ATP per glucose molecule

Answer

Glycolysis produces 2 molecules of pyruvate

Answer

Hexokinase consumes ATP during glycolysis

Answer

Aldolase catalyzes the conversion of fructose-1,6-bisphosphate into two three-carbon molecules

Question 5

Which of the following substances does not inhibit glycolysis?

Accepted Answer

Fluoroacetate

Answer

Fluoride

Answer

Arsenite

Answer

Iodoacetate

Question 6

Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?

Accepted Answer

Muscle

Answer

Liver

Answer

Kidney

Answer

Adipose tissue

Question 7

Mutation in GLUT-2 causes which syndrome?

Accepted Answer

Fanconi-Bickel syndrome

Answer

Dandy walker syndrome

Answer

Beckwith-Wiedemann syndrome

Answer

Menke's disease

Question 8

Which of the following is monoenoic acid ?

Accepted Answer

Oleic acid

Answer

Linoleic acid

Answer

Linolenic acid

Answer

Arachidonic acid

Question 9

Which of the following fatty acids has the maximum number of carbon atoms?

Accepted Answer

Cervonic acid

Answer

Oleic acid

Answer

Linolenic acid

Answer

Arachidonic acid

Question 10

Chylomicron remnants are associated with ?

Accepted Answer

Apo-E

Answer

Apo-C

Answer

Apo-A

Answer

Apo-B100

NEET-PG 2012 — Biochemistry