INI-CET 2022 - Biochemistry PYQs Practice Questions

Q: Match the following molecules with their carriers in plasma: MOLECULES: 1. Thyroxine 2. Fatty acid 3. Hemoglobin 4. Heme CARRIERS: A. Hemopexin B. Prealbumin C. Albumin D. Haptoglobin

1-B, 2-C, 3-D, 4-A. ***1-B, 2-C, 3-D, 4-A*** - **Thyroxine** is primarily transported by **prealbumin (transthyretin)**, which has high affinity for thyroid hormones and prevents their rapid clearance. - **Fatty acids** bind to **albumin** at multiple binding sites, allowing efficient transport of these hydrophobic molecules in plasma. - **Hemoglobin** released from lysed red blood cells is bound by **haptoglobin** to prevent renal loss and iron wastage. - **Heme** groups are specifically transported by **hemopexin**, which has the highest binding affinity for heme among plasma proteins. *1-B, 2-C, 3-A, 4-D* - Incorrectly pairs **hemoglobin** with hemopexin; hemoglobin binds to **haptoglobin** to form stable complexes. - Incorrectly pairs **heme** with haptoglobin; free heme has highest affinity for **hemopexin**, not haptoglobin. *1-A, 2-B, 3-C, 4-D* - Incorrectly pairs **thyroxine** with hemopexin; thyroxine is primarily carried by **prealbumin** and thyroxine-binding globulin. - Incorrectly pairs **fatty acids** with prealbumin; fatty acids bind predominantly to **albumin** due to its multiple hydrophobic binding sites. *1-A, 2-D, 3-B, 4-C* - Incorrectly pairs **heme** with albumin; while albumin can bind heme weakly, **hemopexin** is the specific high-affinity carrier. - Incorrectly pairs **hemoglobin** with prealbumin; free hemoglobin forms specific complexes with **haptoglobin** for recycling. [Practice more Biochemistry PYQs on OnCourse]

Q: Cyclooxygenase plays a role in which pathway?

Prostaglandin. ***Prostaglandin*** - **Cyclooxygenase (COX)** enzymes specifically catalyze the conversion of **arachidonic acid** into **prostaglandins**, **prostacyclins**, and **thromboxanes**. - This pathway is crucial for mediating **inflammation**, **fever**, and **pain** responses in the body. *Leukotriene* - **Leukotrienes** are synthesized via the **lipoxygenase** pathway, not the cyclooxygenase pathway. - They are primarily involved in **allergic reactions** and **asthma**, causing bronchoconstriction and increased vascular permeability. *Vitamin K* - **Vitamin K** is a fat-soluble vitamin essential for the synthesis of **blood clotting factors** and does not involve cyclooxygenase enzymes. - It acts as a cofactor for the enzyme **gamma-glutamyl carboxylase**. *Krebs cycle* - The **Krebs cycle (citric acid cycle)** is a central metabolic pathway for **cellular respiration**, producing ATP, NADH, and FADH2. - It takes place in the **mitochondria** and is involved in the breakdown of carbohydrates, fats, and proteins for energy, unrelated to cyclooxygenase. [Practice more Biochemistry PYQs on OnCourse]

Q: Which is the correct sequence of steps in isolating desirable protein using recombinant DNA technology? 1. Expression of protein and lysis of the bacterial cell 2. Incorporation of genes into bacteria 3. SDS PAGE 4. Protein elution 5. Column chromatography

2,1,3,5,4. ***2,1,3,5,4*** - This sequence accurately reflects the typical order of operations in **recombinant protein isolation**: first, the gene is introduced into bacteria, then protein is expressed and cells lysed, followed by **SDS-PAGE as an intermediate quality check** to confirm protein expression before proceeding to purification steps (column chromatography and elution). - The process starts with gene incorporation, includes an analytical checkpoint after lysis, and ends with purified protein elution. *2,4,5,3,1* - This sequence is incorrect because **protein elution (4)** and **column chromatography (5)** are purification steps that occur *after* protein expression and cell lysis. - **Lysis (1)** cannot happen after elution, as cells must be lysed first to release the protein for purification. *1,2,4,3,5* - This sequence is incorrect because **expression and lysis (1)** must occur *after* the gene has been **incorporated into bacteria (2)** - the gene must be present before it can be expressed. - Additionally, **protein elution (4)** should follow **column chromatography (5)**, as elution is the step where protein is collected from the chromatography column. *1,5,2,4,3* - This sequence is incorrect because **incorporation of genes (2)** must be the first step - the gene needs to be in the bacteria before any expression, lysis, or purification can occur. - Starting with **expression and lysis (1)** before gene incorporation is impossible. [Practice more Biochemistry PYQs on OnCourse]

Q: In a patient with maple syrup urine disease, all of the following amino acids should be restricted in diet except?

Methionine. ***Methionine*** - **Maple syrup urine disease (MSUD)** is a disorder affecting the metabolism of **branched-chain amino acids (BCAAs)**: leucine, isoleucine, and valine. - Therefore, methionine, which is not a BCAA, typically does not need to be restricted and is, in fact, an **essential amino acid** crucial for protein synthesis. *Isoleucine* - **Isoleucine** is a branched-chain amino acid (BCAA) whose metabolism is impaired in MSUD due to a deficiency in **branched-chain alpha-keto acid dehydrogenase complex**. - Accumulation of isoleucine and its corresponding alpha-keto acid is toxic and must be **restricted in the diet**. *Leucine* - **Leucine** is another branched-chain amino acid (BCAA) that cannot be properly metabolized in MSUD. - High levels of leucine and its metabolites are particularly **neurotoxic** and contribute to the characteristic neurological symptoms, necessitating strict dietary restriction. *Valine* - **Valine** is the third branched-chain amino acid (BCAA) whose breakdown is defective in MSUD. - Dietary restriction of valine is essential to prevent its accumulation, which can lead to metabolic crises and **developmental delays**. [Practice more Biochemistry PYQs on OnCourse]

Q: Deamination of methylated cytosine forms which of the following?

Thymine. ***Thymine*** - Deamination of **5-methylcytosine** removes the amine group at the 4-position and replaces it with a keto group, forming **thymine**. - This reaction can lead to a common type of point mutation, as the DNA repair machinery might fail to distinguish this naturally occurring base from normal thymine. *Uracil* - **Uracil** is formed by the deamination of **unmethylated cytosine**, not methylated cytosine. - Uracil is a base found in RNA but not typically in DNA, so its presence in DNA signals a repair event. *Cytosine* - **Cytosine** is the original base before deamination occurs; deamination is a chemical modification that changes cytosine into another base. - If a base remains cytosine, it means deamination has not taken place. *Guanine* - **Guanine** is a purine base and is structurally unrelated to cytosine or its deamination products. - Deamination primarily affects pyrimidine bases like cytosine and uracil, not purines like guanine. [Practice more Biochemistry PYQs on OnCourse]

Question 1

Match the following molecules with their carriers in plasma:

MOLECULES:
1. Thyroxine
2. Fatty acid
3. Hemoglobin
4. Heme

CARRIERS:
A. Hemopexin
B. Prealbumin
C. Albumin
D. Haptoglobin

Accepted Answer

1-B, 2-C, 3-D, 4-A

Answer

1-B, 2-C, 3-A, 4-D

Answer

1-A, 2-B, 3-C, 4-D

Answer

1-A, 2-D, 3-B, 4-C

Question 2

Cyclooxygenase plays a role in which pathway?

Accepted Answer

Prostaglandin

Answer

Leukotriene

Answer

Vitamin K

Answer

Krebs cycle

Question 3

Which is the correct sequence of steps in isolating desirable protein using recombinant DNA technology?

1. Expression of protein and lysis of the bacterial cell
2. Incorporation of genes into bacteria
3. SDS PAGE
4. Protein elution
5. Column chromatography

Accepted Answer

2,1,3,5,4

Answer

2,4,5,3,1

Answer

1,2,4,3,5

Answer

1,5,2,4,3

Question 4

In a patient with maple syrup urine disease, all of the following amino acids should be restricted in diet except?

Accepted Answer

Methionine

Answer

Isoleucine

Answer

Leucine

Answer

Valine

Question 5

Deamination of methylated cytosine forms which of the following?

Accepted Answer

Thymine

Answer

Uracil

Answer

Cytosine

Answer

Guanine

Question 6

Increased H+ ions in the intermembrane space of mitochondria are due to?

Accepted Answer

Increased electron transport chain activity

Answer

Decreased ATP synthase activity

Answer

Reduced proton pumping

Answer

Impaired inner mitochondrial membrane integrity

Question 7

The signal sequence in a type 2 membrane protein with N-terminal facing cytoplasm is located in?

Accepted Answer

Middle of protein

Answer

C-terminal

Answer

Both N and C terminal

Answer

N-terminal

INI-CET 2022 — Biochemistry