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

Which of the following enzymes is classified as a serine protease?

Accepted Answer

Trypsin

Answer

Pepsin

Answer

Carboxypeptidase

Answer

None of the options

Question 8

Primary hypercholesterolemia is:

Accepted Answer

Type IIa

Answer

Type I

Answer

Type IIb

Answer

Type III

Question 9

Which of the following trace elements has vitamin E-like action?

Accepted Answer

Selenium

Answer

Iron

Answer

Copper

Answer

Zinc

Question 10

Which type of RNA is most commonly associated with pseudouridine?

Accepted Answer

transfer RNA (tRNA)

Answer

messenger RNA (mRNA)

Answer

ribosomal RNA (rRNA)

Answer

DNA

NEET-PG 2013 — Biochemistry