FMGE 2019 - Biochemistry PYQs Practice Questions

Q: Keshan's disease is due to deficiency of:

Selenium. **Selenium (Correct Answer)** - **Keshan disease** is an endemic cardiomyopathy characterized by multifocal myocyte necrosis, which has been directly linked to a severe dietary deficiency of **selenium**. - Selenium is an essential component of **glutathione peroxidase**, an enzyme critical for protecting cells against oxidative damage. - The disease is named after Keshan County in China where it was first identified in selenium-deficient regions. *Iron (Incorrect)* - **Iron deficiency** primarily leads to **anemia**, characterized by fatigue, pallor, and weakness due to insufficient hemoglobin production. - It does not directly cause the specific cardiomyopathy seen in Keshan disease. *Zinc (Incorrect)* - **Zinc deficiency** can cause a range of symptoms including impaired immune function, skin lesions (acrodermatitis enteropathica), hair loss, and growth retardation. - It is not associated with the cardiac manifestations of Keshan disease. *Copper (Incorrect)* - **Copper deficiency** can result in anemia, neutropenia, impaired immune function, and neurological dysfunction (Menkes disease). - While copper is important for various metalloenzymes, its deficiency does not cause Keshan disease. [Practice more Biochemistry PYQs on OnCourse]

Q: Zinc is cofactor of which enzyme?

Carbonic anhydrase. ***Carbonic anhydrase*** - **Zinc** is an essential cofactor for **carbonic anhydrase**, crucial for its enzymatic activity in catalyzing the reversible hydration of carbon dioxide. - This enzyme plays a vital role in processes like **pH regulation**, **carbon dioxide transport**, and **bicarbonate production** in various tissues. *Carboxylase* - Carboxylases typically require **biotin** as a cofactor for their activity, which involves the addition of a carboxyl group to a substrate. - Examples include **pyruvate carboxylase** and **acetyl-CoA carboxylase**, which are fundamental in metabolic pathways. *Kinase* - Kinases are enzymes that catalyze the transfer of a **phosphate group** from a high-energy donor molecule (like ATP) to a substrate. - Their activity often depends on cofactors like **magnesium (Mg2+)** or **manganese (Mn2+)**, not zinc. *Lysyl oxidase* - **Lysyl oxidase** is an enzyme that requires **copper** as a cofactor for its activity. - It plays a critical role in the **cross-linking of collagen and elastin**, essential for the integrity of connective tissues. [Practice more Biochemistry PYQs on OnCourse]

Q: All are cofactors for Dehydrogenase except:

SAM. ***SAM*** - **S-adenosylmethionine (SAM)** is a cofactor involved in **methyl group transfer reactions**, carried out by enzymes known as methyltransferases. - Dehydrogenase enzymes catalyze **redox reactions**, typically involving the transfer of hydride ions, and thus do not utilize SAM as a cofactor. *NADP* - **Nicotinamide adenine dinucleotide phosphate (NADP)** is a crucial coenzyme for many **dehydrogenase reactions**, particularly in **anabolic pathways** like fatty acid synthesis and the pentose phosphate pathway. - It acts as an **electron carrier**, accepting or donating hydride ions. *NAD* - **Nicotinamide adenine dinucleotide (NAD)** is a highly common coenzyme for numerous **dehydrogenase enzymes**, especially in **catabolic pathways** such as glycolysis, the Krebs cycle, and oxidative phosphorylation. - It functions as an **electron acceptor** or donor in redox reactions. *FAD* - **Flavin adenine dinucleotide (FAD)** is a coenzyme derived from **riboflavin (Vitamin B2)** and is associated with various dehydrogenase enzymes, particularly those involved in **electron transport** and fatty acid oxidation. - FAD can accept two hydrogen atoms (one hydride and one proton) to become FADH₂. [Practice more Biochemistry PYQs on OnCourse]

Q: Which structure of protein is not denatured after heating up to 100 degrees Celsius?

Primary. ***Primary*** - The **primary structure** refers to the specific linear sequence of **amino acids** forming the polypeptide chain, linked by **covalent peptide bonds**. - These strong **peptide bonds** are generally resistant to heat denaturation at 100°C, meaning the amino acid sequence remains intact. *Quaternary* - The **quaternary structure** involves the arrangement of multiple polypeptide subunits and is maintained by weaker interactions like **hydrophobic interactions**, hydrogen bonds, and salt bridges. - These interactions are highly susceptible to disruption by heat, causing the subunits to dissociate and the quaternary structure to be lost. *Tertiary* - The **tertiary structure** describes the three-dimensional folding of a single polypeptide chain, stabilized by various non-covalent interactions (e.g., hydrogen bonds, ionic bonds, hydrophobic interactions) and **disulfide bonds**. - Heat disrupts these weaker non-covalent interactions and can even break disulfide bonds, leading to the unfolding and loss of the specific 3D shape. *Secondary* - The **secondary structure** (e.g., **alpha-helices** and **beta-pleated sheets**) arises from hydrogen bonds between the backbone atoms of the polypeptide chain. - While peptide bonds remain intact, these vital **hydrogen bonds** are easily broken by heat, causing the unraveling of helices and sheets. [Practice more Biochemistry PYQs on OnCourse]

Q: Most abundant amino acid found in collagen?

Glycine. ***Glycine*** - **Glycine** is the most abundant amino acid in collagen, making up approximately one-third of its total amino acid content. - Its small size (due to a single hydrogen atom as its side chain) is crucial for the formation of the **triple helix structure** of collagen, allowing the tight packing of the three alpha chains. *Hydroxyproline* - **Hydroxyproline** is a modified amino acid derived from proline, and while abundant in collagen, it accounts for about 13% of the total amino acids, less than glycine. - It plays a vital role in stabilizing the collagen triple helix through **hydrogen bonding**. *Proline* - **Proline** is a structurally important amino acid in collagen, contributing to the kinks and turns necessary for the formation of the triple helix. - However, its abundance is less than that of glycine, making up around 10-17% of collagen's amino acids. *Lysine* - **Lysine** is a less abundant but essential amino acid in collagen, making up about 2-5% of its composition. - It is critical for **cross-linking** collagen fibers, which provides tensile strength, and can be hydroxylated to form **hydroxylysine**. [Practice more Biochemistry PYQs on OnCourse]

Question 1

Keshan's disease is due to deficiency of:

Accepted Answer

Selenium

Answer

Iron

Answer

Zinc

Answer

Copper

Question 2

Zinc is cofactor of which enzyme?

Accepted Answer

Carbonic anhydrase

Answer

Carboxylase

Answer

Kinase

Answer

Lysyl oxidase

Question 3

All are cofactors for Dehydrogenase except:

Accepted Answer

SAM

Answer

NADP

Answer

NAD

Answer

FAD

Question 4

Which structure of protein is not denatured after heating up to 100 degrees Celsius?

Accepted Answer

Primary

Answer

Quaternary

Answer

Tertiary

Answer

Secondary

Question 5

Most abundant amino acid found in collagen?

Accepted Answer

Glycine

Answer

Hydroxyproline

Answer

Proline

Answer

Lysine

Question 6

Which is a product of purine metabolism?

Accepted Answer

Uric acid

Answer

Xanthine

Answer

Beta alanine

Answer

Urea

Question 7

Melanin is derived from which amino acid?

Accepted Answer

Tyrosine

Answer

Phenylalanine

Answer

Alanine

Answer

Tryptophan

Question 8

Which bases are present in human DNA?

Accepted Answer

Adenine-guanine-cytosine-thymine

Answer

None of the above

Answer

Adenine-guanine-cytosine-uracil

Answer

Adenine-guanine-thiamine-uracil

Question 9

Type IV complex of ETC is inhibited by

Accepted Answer

Cyanide

Answer

Antimycin

Answer

Oligomycin

Answer

CO2

Question 10

Gluconeogenesis is inhibited by?

Accepted Answer

Insulin

Answer

Cholecystokinin

Answer

5-alpha reductase

Answer

Glucagon

FMGE 2019 — Biochemistry