NEET-PG 2013 - Biochemistry PYQs Practice Questions

Q: What is the major apolipoprotein of chylomicrons?

B-48. ***B-48*** - **Apolipoprotein B-48** is exclusively produced in the intestine and is the **major structural apolipoprotein** found only on **chylomicrons**. - It is critical for the **assembly and secretion of chylomicrons** from intestinal cells into the lymphatic system. - ApoB-48 represents the N-terminal 48% of ApoB-100 and lacks the LDL receptor-binding domain. *B-100* - **Apolipoprotein B-100** is synthesized in the liver and is the primary structural apolipoprotein of **VLDL, IDL, and LDL**. - It acts as the **ligand for the LDL receptor**, facilitating the uptake of cholesterol into cells. *Apo-C* - **Apolipoprotein C (Apo-C)** proteins (e.g., ApoC-II, ApoC-III) are exchangeable apolipoproteins found on several lipoproteins, including chylomicrons, VLDL, and HDL. - **ApoC-II activates lipoprotein lipase**, which hydrolyzes triglycerides, but these are **not structural proteins** and are present in smaller quantities. *Apo-E* - **Apolipoprotein E (Apo-E)** is acquired by chylomicrons in circulation and is important for **chylomicron remnant clearance** by the liver. - While present on chylomicrons, it is **not the major structural apolipoprotein** – that role belongs to ApoB-48. [Practice more Biochemistry PYQs on OnCourse]

Q: Which vitamin is required for transfer of 1-carbon unit?

Folic acid. ***Folic acid*** - **Folic acid** (vitamin B9) is essential for the transfer of **one-carbon units**, particularly as **tetrahydrofolate (THF)**. - These one-carbon units are critical in metabolic processes such as **DNA synthesis**, **amino acid metabolism**, and **neurotransmitter synthesis**. *Vitamin A* - **Vitamin A** (retinol) is primarily involved in **vision**, **immune function**, and **cell differentiation**. - It does not play a direct role in the transfer of one-carbon units. *Vitamin B12* - **Vitamin B12** (cobalamin) is involved in two main reactions: the conversion of **methylmalonyl-CoA to succinyl-CoA** and the transfer of a **methyl group from N5-methyl THF to homocysteine** to form methionine. - While it works with folate, it does not directly transfer one-carbon units in the same way as folic acid. *Niacin* - **Niacin** (vitamin B3) is a precursor to **NAD+ and NADP+**, which are crucial coenzymes in **redox reactions** and energy metabolism. - It is not involved in the transfer of one-carbon units. [Practice more Biochemistry PYQs on OnCourse]

Q: Which of the following is NOT present in DNA?

Uracil. ***Uracil*** - **Uracil** is a pyrimidine nitrogenous base that replaces **thymine** in RNA, meaning it is not found in the structure of DNA. - In RNA, uracil pairs with **adenine** through two hydrogen bonds. *Thymine* - **Thymine** is a pyrimidine found in DNA, where it pairs with **adenine**. - It is replaced by **uracil** in RNA. *Cytosine* - **Cytosine** is a pyrimidine that is a fundamental component of both **DNA** and **RNA**. - In DNA, cytosine pairs with **guanine**. *Adenine* - **Adenine** is a purine that is a fundamental component of both **DNA** and **RNA**. - In DNA, adenine pairs with **thymine**, and in RNA, it pairs with **uracil**. [Practice more Biochemistry PYQs on OnCourse]

Q: Number of ATP molecules formed per turn of the citric acid cycle is

10. ***10*** - Each turn of the citric acid cycle directly produces **1 GTP** molecule (which is equivalent to 1 ATP). - Additionally, it generates **3 NADH** and **1 FADH2**, which upon oxidative phosphorylation yield approximately **2.5 ATP per NADH** and **1.5 ATP per FADH2**. - Total calculation: (3 × 2.5) + (1 × 1.5) + 1 (from GTP) = 7.5 + 1.5 + 1 = **10 ATP equivalents** per turn. *5* - This number is **too low** and does not account for the significant energy yield from the **NADH** and **FADH2** molecules produced during the cycle. - It likely only considers a partial or incorrect calculation of the ATP equivalents generated. *7* - This value is **insufficient** as it underestimates the total ATP generated when considering the contributions from both **direct substrate-level phosphorylation (GTP)** and the **electron transport chain**. - It may arise from an incomplete understanding of the ATP yield from NADH and FADH2. *15* - This number is **too high** for the ATP equivalents produced per turn of the citric acid cycle. - Such a value would imply a higher energy yield from the electron carriers or direct ATP production than is biologically accurate. [Practice more Biochemistry PYQs on OnCourse]

Q: Which of the following amino acids is found in keratin?

All of the options. ***All of the options*** - **Keratin** is a fibrous structural protein that forms the main component of hair, skin, and nails - All three amino acids listed - **Histidine, Lysine, and Arginine** - are indeed found in keratin's composition - **Lysine** and **Arginine** are basic amino acids that contribute to keratin's structural stability and are involved in ionic interactions - **Histidine** is also present and plays a role in the protein's functional and structural aspects - While keratin is particularly rich in **cysteine** (which forms disulfide bonds responsible for its strength), it also contains significant amounts of these other amino acids - The complete amino acid composition of keratin includes all of these and many other amino acids working together to provide its characteristic properties *Why individual options alone are incomplete* - Selecting only **Histidine**, **Lysine**, or **Arginine** individually would be incorrect because it would imply the other amino acids are NOT found in keratin - Since the question asks which amino acid "is found" in keratin and all three ARE present, the correct answer must acknowledge all of them [Practice more Biochemistry PYQs on OnCourse]

Question 1

What is the major apolipoprotein of chylomicrons?

Accepted Answer

B-48

Answer

B-100

Answer

Apo-C

Answer

Apo-E

Question 2

Which vitamin is required for transfer of 1-carbon unit?

Accepted Answer

Folic acid

Answer

Niacin

Answer

Vitamin B12

Answer

Vitamin A

Question 3

Which of the following is NOT present in DNA?

Accepted Answer

Uracil

Answer

Thymine

Answer

Adenine

Answer

Cytosine

Question 4

Number of ATP molecules formed per turn of the citric acid cycle is

Accepted Answer

10

Answer

5

Answer

7

Answer

15

Question 5

Which of the following amino acids is found in keratin?

Accepted Answer

All of the options

Answer

Lysine

Answer

Histidine

Answer

Arginine

Question 6

Which form of tetrahydrofolate (THF) serves as the central intermediate in the one-carbon pool and is most directly involved in thymidine synthesis?

Accepted Answer

Methylene THF

Answer

None of the options

Answer

Methyl THF

Answer

Formyl THF

Question 7

Glucagon stimulates

Accepted Answer

Gluconeogenesis

Answer

Glycogenesis

Answer

Fatty acid synthesis

Answer

Glycolysis

Question 8

What is the primary reason for the detergent action of bile salts?

Accepted Answer

Amphipathic nature

Answer

Hydrophobic properties

Answer

Acts as a zwitterion

Answer

None of the options

Question 9

Reducing equivalents produced in glycolysis are transported from cytosol to mitochondria by ?

Accepted Answer

Malate-aspartate shuttle

Answer

Carnitine

Answer

Creatine

Answer

Glutamate shuttle

Question 10

Trypsinogen is converted to trypsin by?

Accepted Answer

Removal of specific amino acids from trypsinogen

Answer

Combination of 2 molecules of trypsinogen

Answer

Phosphorylation

Answer

Addition of alkyl group

NEET-PG 2013 — Biochemistry