NEET-PG 2019 - Biochemistry PYQs Practice Questions

Q: Which of the following is true about alpha-1 antitrypsin?

Inhibits elastase. ***Inhibits elastase*** - Alpha-1 antitrypsin (A1AT) primarily serves to **inhibit elastase**, a protease that can damage lung tissue, helping to protect the lungs from destruction [1]. - Deficiency of A1AT leads to **emphysema** and liver disease due to unchecked activity of elastase [1][2]. *Inhibits trypsin* - A1AT specifically does not primarily inhibit **trypsin**, which is involved in protein digestion in the intestine. - Although A1AT affects proteases, its main function is related to **elastase**, not trypsin [1]. *Inhibits trypsinogen activation in pancreas* - A1AT does not have a significant role in the **inhibition of trypsinogen activation** within the pancreas. - Instead, pancreatic enzyme regulation involves other mechanisms that do not involve A1AT's function. *Inhibits chymotrypsin* - A1AT is not known for inhibiting **chymotrypsin**, a serine protease derived from trypsinogen in the gut. - It specifically targets **elastase** and similar enzymes rather than chymotrypsin [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 856-858. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 683-684. [Practice more Biochemistry PYQs on OnCourse]

Q: Which of the following is not the source of cytosolic NADPH ?

ATP citrate lyase. ***ATP citrate lyase*** - **ATP citrate lyase** is an enzyme involved in the synthesis of **acetyl-CoA** from citrate in the cytosol, which is then used for **fatty acid synthesis**. It does not generate NADPH. - While the **acetyl-CoA** produced is used in pathways that require NADPH, ATP citrate lyase itself does not directly produce NADPH. *Isocitrate dehydrogenase* - Cytosolic **isocitrate dehydrogenase** catalyzes the oxidative decarboxylation of **isocitrate** to alpha-ketoglutarate, producing **NADPH**. - This reaction is an important source of **cytosolic NADPH**, especially in non-photosynthetic tissues. *Malic enzyme* - **Malic enzyme** catalyzes the oxidative decarboxylation of **malate** to pyruvate, simultaneously reducing **NADP+ to NADPH**. - This enzyme is a significant source of **cytosolic NADPH** in various tissues, contributing to fatty acid synthesis and other reductive processes. *G6PD* - **Glucose-6-phosphate dehydrogenase (G6PD)** is the rate-limiting enzyme in the **pentose phosphate pathway** (PPP). - It catalyzes the first step of the PPP, converting **glucose-6-phosphate** to 6-phosphogluconolactone and producing **NADPH** as a crucial coenzyme. [Practice more Biochemistry PYQs on OnCourse]

Q: Conversion of Norepinephrine to epinephrine is mainly by?

S-adenosyl methionine. **S-adenosyl methionine (SAM)** - SAM acts as the **methyl donor** in the enzymatic conversion of **norepinephrine to epinephrine** by phenylethanolamine N-methyltransferase (PNMT). - This **methylation reaction** adds a methyl group to the nitrogen atom of norepinephrine, forming epinephrine. *Arginine* - Arginine is a precursor for **nitric oxide (NO)** synthesis, an important signaling molecule, and is also involved in the **urea cycle**. - It is not directly involved in the methylation of norepinephrine to epinephrine. *Phenylalanine* - Phenylalanine is an **essential amino acid** and a precursor for the synthesis of **tyrosine**, which is subsequently converted to **catecholamines** like dopamine, norepinephrine, and epinephrine. - However, it does not directly facilitate the final conversion step from norepinephrine to epinephrine. *Dehydrogenase* - Dehydrogenases are enzymes that catalyze **redox reactions** by removing hydrogen atoms from a substrate. - These enzymes are crucial in many metabolic pathways, but they are not involved in the **methylation reaction** that converts norepinephrine to epinephrine. [Practice more Biochemistry PYQs on OnCourse]

Q: Menkes disease is caused by a deficiency of which protein?

ATP7A (copper-transporting ATPase). ***ATP7A (copper-transporting ATPase)*** - **Menkes disease** is an X-linked recessive disorder caused by a mutation in the **ATP7A gene**, which encodes a copper-transporting ATPase. - This protein is essential for **copper absorption** from the intestines and its transport across cell membranes. *ATP7B (Wilson disease protein)* - Mutations in the **ATP7B gene** cause **Wilson disease**, characterized by **copper accumulation** in the liver, brain, and other organs due to impaired copper excretion. - Unlike Menkes disease, Wilson disease involves *too much* copper in tissues, not a deficiency due to poor absorption. *Ceruloplasmin* - **Ceruloplasmin** is a copper-carrying protein that transports copper in the blood and also acts as an oxidase. - While deficiencies in ceruloplasmin can lead to **aceruloplasminemia**, a disorder of iron metabolism, it is not the primary defect in Menkes disease. *Copper-zinc superoxide dismutase* - **Copper-zinc superoxide dismutase (SOD1)** is an enzyme that plays a crucial role in eliminating harmful **reactive oxygen species**. - Mutations in SOD1 are associated with some forms of **amyotrophic lateral sclerosis (ALS)**, not Menkes disease. [Practice more Biochemistry PYQs on OnCourse]

Q: A 25-year-old alcoholic presented with edema, hypertension, ocular disturbance, and changes in mental state. A diagnosis of high output cardiac failure was made with Wet Beri Beri. This condition is due to a deficiency of which vitamin?

Vitamin B1. Vitamin B1 - The constellation of **edema**, **hypertension**, **ocular disturbances**, and **mental status changes** in an **alcoholic** patient with **high-output cardiac failure** (Wet Beri Beri) is a classic presentation of **thiamine (Vitamin B1) deficiency** [2], [3]. - **Thiamine** is crucial for **carbohydrate metabolism** and **neurological function**, and a deficiency can lead to severe cardiovascular and neurological dysfunction, especially in chronic alcoholics due to poor absorption and increased metabolic demand [1], [3]. Vitamin B3 - Deficiency of Vitamin B3 (niacin) causes **pellagra**, characterized by the "4 D's": **dermatitis**, **diarrhea**, **dementia**, and death. - While it can cause psychiatric symptoms (dementia), it does not directly lead to the specific cardiovascular manifestations of high-output cardiac failure as seen in Wet Beri Beri. Vitamin B6 - Deficiency of Vitamin B6 (pyridoxine) can result in **peripheral neuropathy**, **anemia**, and **seizures**. - It is not directly linked to the cardiac and edematous symptoms characteristic of Wet Beri Beri. Vitamin B9 - Deficiency of Vitamin B9 (folate) primarily causes **megaloblastic anemia** and can lead to **neural tube defects** in developing fetuses. - While it can manifest with fatigue and weakness due to anemia, it does not typically present with the acute cardiovascular and neurological syndrome described. [Practice more Biochemistry PYQs on OnCourse]

Question 1

Which of the following is true about alpha-1 antitrypsin?

Accepted Answer

Inhibits elastase

Answer

Inhibits trypsin

Answer

Inhibits chymotrypsin

Answer

Inhibits trypsinogen activation

Question 2

Which of the following is not the source of cytosolic NADPH ?

Accepted Answer

ATP citrate lyase

Answer

Malic enzyme

Answer

G6PD

Answer

Isocitrate dehydrogenase

Question 3

Conversion of Norepinephrine to epinephrine is mainly by?

Accepted Answer

S-adenosyl methionine

Answer

Arginine

Answer

Phenylalanine

Answer

Dehydrogenase

Question 4

Menkes disease is caused by a deficiency of which protein?

Accepted Answer

ATP7A (copper-transporting ATPase)

Answer

ATP7B (Wilson disease protein)

Answer

Ceruloplasmin

Answer

Copper-zinc superoxide dismutase

Question 5

A 25-year-old alcoholic presented with edema, hypertension, ocular disturbance, and changes in mental state. A diagnosis of high output cardiac failure was made with Wet Beri Beri. This condition is due to a deficiency of which vitamin?

Accepted Answer

Vitamin B1

Answer

Vitamin B3

Answer

Vitamin B6

Answer

Vitamin B9

Question 6

In Krebs cycle and Urea cycle the linking amino acid is

Accepted Answer

Aspartate

Answer

Fumarate

Answer

Alanine

Answer

Arginine

Question 7

Hyperammonaemia inhibits the TCA cycle by depleting which of the following?

Accepted Answer

α-ketoglutarate

Answer

succinate

Answer

malate

Answer

fumarate

Question 8

MRP2 associated with which of the following?

Accepted Answer

Dubin-Johnson syndrome

Answer

Rotor syndrome

Answer

Crigler-Najjar syndrome

Answer

Gilbert syndrome

Question 9

All of the following are examples of Dietary fibre except for which of the following?

Accepted Answer

Starch

Answer

Pectin

Answer

Lignin

Answer

Cellulose

Question 10

Which of the following statements regarding mitochondrial DNA is FALSE?

Accepted Answer

All respiratory proteins are synthesized within the mitochondria

Answer

Double stranded

Answer

Inherited from mother

Answer

High mutation rate

NEET-PG 2019 — Biochemistry