NEET-PG 2013 - Biochemistry Practice Questions

Q: Which of the following statements about vitamin E is false?

Water soluble vitamin. ***Water soluble vitamin*** - This statement is false because **vitamin E** is a **fat-soluble vitamin**, meaning it dissolves in lipids and is stored in the body's fatty tissues and liver. - Its absorption requires the presence of dietary fat and bile salts, unlike water-soluble vitamins. *Act as antioxidant* - **Vitamin E** is a powerful **lipid-soluble antioxidant**, protecting cell membranes from damage by scavenging **free radicals**. - It helps prevent **oxidative damage** to polyunsaturated fatty acids within cell membranes. *Chemically tocopherol* - The most biologically active form of **vitamin E** is **alpha-tocopherol**, although vitamin E encompasses a group of eight fat-soluble compounds, including tocopherols and tocotrienols. - This term correctly identifies the chemical nature of the prominent forms of vitamin E. *Prevent lipid peroxidation of cell membrane* - As an **antioxidant**, **vitamin E** specifically interferes with the **propagation of lipid peroxidation**, a chain reaction that damages cell membranes by oxidizing their lipid components. - It donates an electron to **free radicals**, thereby neutralizing them and protecting the integrity of the cell membrane.

Q: Which mineral is known for its antioxidant properties similar to those of vitamin E?

Selenium. ***Selenium*** - Selenium is a crucial component of **glutathione peroxidase**, an enzyme with significant **antioxidant properties** that protects cells from oxidative damage. - Its antioxidant function is often compared to that of **vitamin E**, as both work to neutralize **free radicals** in the body. *Calcium* - Calcium is primarily known for its role in **bone health**, muscle contraction, and **nerve transmission**, not for its antioxidant properties. - It does not directly participate in neutralizing free radicals like selenium or vitamin E. *Iron* - Iron is essential for **oxygen transport** in red blood cells and various metabolic processes. - While crucial, excessive free iron can actually promote the formation of **free radicals** (Fenton reaction), making it pro-oxidant rather than antioxidant. *Magnesium* - Magnesium is involved in over 300 enzymatic reactions, including **energy metabolism** and muscle and nerve function. - It does not share direct antioxidant properties similar to vitamin E or selenium.

Q: What is the blood form of folic acid?

Methyltetrahydrofolate. ***Methyltetrahydrofolate*** - **5-methyltetrahydrofolate (5-MTHF)** is the **primary circulating form** of folate in the blood plasma and the most metabolically active form of folate. - It plays a crucial role in various metabolic pathways, especially in **one-carbon metabolism** for DNA synthesis and repair. *Folinic acid* - **Folinic acid** (leucovorin) is a **reduced form of folic acid** that does not require reduction by dihydrofolate reductase for activity. - It is often used as a therapeutic agent, particularly to **counteract the effects of methotrexate** toxicity, but it is not the main physiological circulating form. *Pteroglutamate* - **Pteroglutamate** is a generic term referring to compounds structurally related to folic acid, which is itself chemically known as pteroylglutamic acid. - While it describes the **general structure**, it is not the specific blood form of folic acid. *None of the options* - This option is incorrect because **methyltetrahydrofolate** is indeed the correct answer.

Q: Which vitamin is primarily involved in redox reactions?

Riboflavin. ***Riboflavin*** - **Riboflavin** (Vitamin B2) is a precursor to **flavin adenine dinucleotide (FAD)** and **flavin mononucleotide (FMN)**, which are crucial coenzymes in many **redox reactions**. - These coenzymes act as electron carriers in metabolic pathways, including the **electron transport chain**, where they accept and donate electrons. *Pyridoxine* - **Pyridoxine** (Vitamin B6) is primarily involved in **amino acid metabolism**, including transamination, decarboxylation, and racemization. - It functions as **pyridoxal phosphate (PLP)**, a coenzyme for many enzymes in these pathways, but not directly in redox reactions. *Biotin* - **Biotin** (Vitamin B7) is a coenzyme for **carboxylase enzymes**, which are involved in carboxylation reactions (addition of a carboxyl group). - Its main roles are in **fatty acid synthesis**, gluconeogenesis, and leucine metabolism, not direct redox reactions. *Folic acid* - **Folic acid** (Vitamin B9) is essential for **one-carbon metabolism**, involved in transferring one-carbon units in the synthesis of nucleotides (DNA/RNA) and amino acids. - It functions as **tetrahydrofolate (THF)**, playing a critical role in cell division and growth, but not as a direct redox agent.

Q: Which is not a dietary fiber ?

Lactulose. ***Lactulose*** - **Lactulose is NOT a dietary fiber** - it is a synthetic disaccharide used pharmaceutically as an osmotic laxative and for treating hepatic encephalopathy. - Unlike true dietary fibers, lactulose is a manufactured drug, not a naturally occurring food component. - While it is fermented by colonic bacteria (similar to fiber), it does not meet the definition of dietary fiber. *Lignin* - Lignin is a complex aromatic polymer that provides structural support to plant cell walls. - It is classified as a non-polysaccharide dietary fiber that is largely indigestible by human enzymes. - Contributes to fecal bulk and is considered an insoluble fiber. *Pectin* - Pectin is a soluble dietary fiber found naturally in fruits, particularly in apple peels and citrus fruits. - Forms a gel when mixed with water, slowing gastric emptying and aiding digestion. - Beneficial for gut health and blood glucose regulation. *Cellulose* - Cellulose is the most abundant dietary fiber and a major structural component of plant cell walls. - An insoluble fiber composed of β-1,4-linked glucose polymers that cannot be digested by human enzymes. - Contributes to stool bulk and promotes regular bowel movements.

Q: Clinical effect of vitamin D is reduced by ?

Simultaneous ingestion of phytates. ***Simultaneous ingestion of phytates*** - **Phytates (phytic acid)** found in whole grains, nuts, seeds, and legumes can **reduce the clinical effect of vitamin D** through multiple mechanisms - Phytates **chelate calcium** and form insoluble calcium-phytate complexes, reducing calcium absorption - Since **vitamin D and calcium metabolism are closely linked**, impaired calcium absorption indirectly reduces vitamin D efficacy - Phytates can also **directly bind to vitamin D** in the gastrointestinal tract, reducing its bioavailability - Studies show that **high phytate intake increases vitamin D requirements** and can impair vitamin D status *Simultaneous ingestion of lactose* - Lactose does **not reduce** vitamin D absorption or efficacy - In fact, **dairy products are commonly fortified** with vitamin D, and the presence of lactose does not interfere with its beneficial effects - Lactose may actually **enhance calcium absorption**, which works synergistically with vitamin D *Acidic environment* - Vitamin D is a **fat-soluble vitamin** absorbed primarily in the small intestine - An acidic environment (stomach acid) is **not known to inhibit** vitamin D absorption - The absorption process occurs in the **alkaline environment of the small intestine** where fat-soluble vitamins are absorbed with dietary fats *None of the options* - This is **incorrect** as phytates do reduce the clinical effect of vitamin D through calcium chelation and direct binding mechanisms

Q: What is the number of variable regions present on each light and heavy chain of an antibody?

1. ***1*** - Each **light chain** and **heavy chain** within an antibody molecule contains **one variable region (V domain)**. - These variable regions are crucial for **antigen binding specificity**, as they combine to form the antigen-binding site. - The variable domain is located at the **N-terminal end** of each chain. *2* - While a complete antibody molecule has **two antigen-binding sites** (bivalent), each formed by pairing of VH and VL domains, individual chains possess only **one variable region each**. - The number '2' refers to the total number of identical binding sites on the intact antibody, not the number of variable regions per chain. *3* - The number **3** does not correspond to the number of variable regions on individual chains. - This might be confused with the **three complementarity-determining regions (CDRs)** present within each variable domain (CDR1, CDR2, CDR3), which are hypervariable loops that directly contact the antigen. *4* - The number **4** is incorrect for variable regions. - This number corresponds to the total number of **polypeptide chains** in a complete IgG antibody (2 heavy + 2 light chains), or the number of **constant domains** in some heavy chain isotypes (IgM, IgE have 4 CH domains).

Q: What is the role of Anandamide in the human body?

Cannabinoid neurotransmitter. ***Cannabinoid neurotransmitter*** - **Anandamide** is an **endogenous cannabinoid neurotransmitter** that binds to **CB1** and **CB2 receptors**. - It plays a role in **pain modulation**, **appetite stimulation**, and **memory regulation**. *Opioid* - **Opioids** bind to **opioid receptors** (mu, delta, kappa) and are known for their **analgesic** and **euphoric effects**. - Examples include **morphine** and **endorphins**, which are chemically distinct from anandamide and have different receptor targets. *CK 1 antagonist* - This option refers to a **cholecystokinin 1 (CCK1) receptor antagonist**, which would block the effects of **CCK**. - **CCK** is a hormone involved in **digestion** and **satiety**, and its role is unrelated to anandamide. *D2 blocker* - A **D2 blocker** is an agent that antagonizes the **dopamine D2 receptor**. - These are typically **antipsychotic medications** that modulate **dopamine pathways** in the brain, unrelated to the function of anandamide.

Q: Which immunoglobulin is known to be heat-labile?

IgM. ***IgM*** - **IgM** is known for its **heat lability** and is readily denatured at 56°C within a few minutes. - This characteristic is due to its **pentameric structure** held together by disulfide bonds and J chains, which are sensitive to thermal denaturation. - Heat lability of IgM is clinically important in complement fixation tests and other laboratory assays where heat inactivation is performed. - IgM is the first antibody produced in primary immune response and its heat sensitivity distinguishes it from other immunoglobulins. *IgA* - **IgA** exists in monomeric (serum) and dimeric (secretory) forms and shows moderate stability to heat. - Secretory IgA is relatively stable as it needs to function in harsh mucosal environments, though not as heat-resistant as IgG. - Does not exhibit the pronounced heat lability characteristic of IgM. *IgG* - **IgG** is the most stable immunoglobulin and is highly resistant to heat denaturation. - Can withstand temperatures up to 60-70°C without significant loss of activity. - Its monomeric structure with strong intramolecular bonds provides exceptional thermal stability. - Most abundant antibody in serum and has the longest half-life. *IgE* - **IgE** is actually quite stable to heat and can withstand 56°C for extended periods. - While it has a short half-life in serum (2-3 days), this is due to receptor binding rather than heat instability. - Important in type I hypersensitivity reactions and parasitic infections. - Does not show the characteristic heat lability that defines IgM.

Q: Which of the following is not an acute phase reactant?

Endothelin. ***Endothelin*** - Endothelin is a **vasoconstrictive peptide** primarily involved in regulating **blood vessel tone** and blood pressure. - While it plays a role in processes like inflammation and tissue repair, it is not synthesized or regulated in the same rapid, systemic manner as a classic acute phase reactant. *C-reactive protein* - **C-reactive protein (CRP)** is a rapidly responding acute phase reactant produced by the liver in response to **inflammation**, infection, and tissue injury. - Its levels can rise dramatically within hours of an inflammatory stimulus and are used as a marker for disease activity. *Haptoglobin* - **Haptoglobin** is an acute phase reactant that binds to free **hemoglobin** released from red blood cells during hemolysis, preventing oxidative damage. - Its levels typically increase during acute inflammation or infection, although it can also decrease with severe hemolysis. *Fibrinogen* - **Fibrinogen** is a critical acute phase protein involved in the **coagulation cascade** and wound healing. - Its concentration increases significantly during acute inflammation, contributing to the elevated **erythrocyte sedimentation rate (ESR)**.

Question 1

Which of the following statements about vitamin E is false?

Accepted Answer

Water soluble vitamin

Answer

Act as antioxidant

Answer

Chemically tocopherol

Answer

Prevent lipid peroxidation of cell membrane

Question 2

Which mineral is known for its antioxidant properties similar to those of vitamin E?

Accepted Answer

Selenium

Answer

Calcium

Answer

Iron

Answer

Magnesium

Question 3

What is the blood form of folic acid?

Accepted Answer

Methyltetrahydrofolate

Answer

Folinic acid

Answer

Pteroglutamate

Answer

None of the options

Question 4

Which vitamin is primarily involved in redox reactions?

Accepted Answer

Riboflavin

Answer

Pyridoxine

Answer

Biotin

Answer

Folic acid

Question 5

Which is not a dietary fiber ?

Accepted Answer

Lactulose

Answer

Lignin

Answer

Pectin

Answer

Cellulose

Question 6

Clinical effect of vitamin D is reduced by ?

Accepted Answer

Simultaneous ingestion of phytates

Answer

Simultaneous ingestion of lactose

Answer

None of the options

Answer

Acidic environment

Question 7

What is the number of variable regions present on each light and heavy chain of an antibody?

Accepted Answer

1

Answer

2

Answer

3

Answer

4

Question 8

What is the role of Anandamide in the human body?

Accepted Answer

Cannabinoid neurotransmitter

Answer

Opioid

Answer

D2 blocker

Answer

CCK1 antagonist

Question 9

Which immunoglobulin is known to be heat-labile?

Accepted Answer

IgM

Answer

IgA

Answer

IgG

Answer

IgE

Question 10

Which of the following is not an acute phase reactant?

Accepted Answer

Endothelin

Answer

C-reactive protein

Answer

Haptoglobin

Answer

Fibrinogen

NEET-PG 2013 — Biochemistry