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: In Krebs cycle and Urea cycle the linking amino acid is

Aspartate. ***Aspartate*** - **Aspartate** acts as the crucial amino acid link between the two cycles - In the urea cycle, aspartate condenses with citrulline to form **argininosuccinate** (via argininosuccinate synthetase) - When argininosuccinate is cleaved, it produces **fumarate**, which enters the Krebs cycle - In the Krebs cycle, fumarate is converted to malate, then to **oxaloacetate**, which can be transaminated back to aspartate - This creates the **aspartate-argininosuccinate shunt**, linking both cycles through nitrogen metabolism *Fumarate* - While **fumarate** is a key metabolic intermediate connecting both cycles, it is **not an amino acid** (it's a dicarboxylic acid) - It is produced in the urea cycle from argininosuccinate cleavage and feeds into the Krebs cycle - This is a common distractor since fumarate does link the cycles, but the question specifically asks for an amino acid *Alanine* - **Alanine** participates in the glucose-alanine cycle for nitrogen transport from muscle to liver - It does not directly link the Krebs cycle and urea cycle in the same manner as aspartate *Arginine* - **Arginine** is a urea cycle intermediate that is cleaved by arginase to produce urea and ornithine - While it's an amino acid in the urea cycle, it does not serve as the linking amino acid between the Krebs cycle and urea cycle [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: What is the type of cholesterol primarily found in gallstones?

Crystalline cholesterol monohydrate.. ***Crystalline cholesterol monohydrate*** - The predominant type of cholesterol found in gallstones is **crystalline cholesterol monohydrate** [1], which reflects the solid form of cholesterol precipitating in bile. - It is often associated with **cholesterol gallstones**, occurring when bile contains excessive cholesterol or insufficient bile salts. *Crystalline Cholesterol dihydrate* - Crystalline cholesterol dihydrate is less commonly associated with gallstones and generally forms in different circumstances, not typical of cholesterol stones. - This type does not represent the main component of gallstones, which primarily consist of monohydrate forms. *Amorphous cholesterol dihydrate* - Amorphous cholesterol dihydrate is not a recognized form typically found in gallstones, as gallstone pathology focuses on crystallized forms. - Amorphous substances are less stable than crystalline forms, making this option unlikely in the context of gallstones. *Amorphous cholesterol monohydrate* - Amorphous cholesterol monohydrate is not the major component found in gallstones; gallstones are more likely to be crystalline in structure. - This form lacks the stable crystalline structure needed to precipitate and form gallstones effectively. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, p. 882. [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

In Krebs cycle and Urea cycle the linking amino acid is

Accepted Answer

Aspartate

Answer

Fumarate

Answer

Alanine

Answer

Arginine

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

What is the type of cholesterol primarily found in gallstones?

Accepted Answer

Crystalline cholesterol monohydrate.

Answer

Amorphous cholesterol monohydrate.

Answer

Amorphous cholesterol dihydrate.

Answer

Crystalline cholesterol dihydrate.

Question 6

Conversion of Norepinephrine to epinephrine is mainly by?

Accepted Answer

S-adenosyl methionine

Answer

Arginine

Answer

Phenylalanine

Answer

Dehydrogenase

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

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 9

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

Question 10

In Wilson’s disease, which of the following substances is excreted in lower amounts in the urine?

Accepted Answer

Methyl- Histidine

Answer

Phosphotyrosine

Answer

Phosphorus

Answer

Serine

NEET-PG 2019 — Biochemistry