NEET-PG 2018 - Biochemistry Practice Questions

Q: What do chaperones assist in?

Protein Folding. ***Protein Folding*** - **Chaperone proteins** bind to newly synthesized polypeptide chains and unfolded proteins, helping them achieve their **correct three-dimensional structure**. - They also prevent **misfolding** and **aggregation** of proteins, which can be detrimental to cellular function. *Protein Cleavage* - **Protein cleavage** involves the enzymatic hydrolysis of peptide bonds, often performed by **proteases**. - This process is not directly facilitated by chaperones; chaperones primarily function in structural maturation, not degradation or processing. *Protein Degradation* - **Protein degradation** is carried out by systems like the **ubiquitin-proteasome pathway** or lysosomes, which break down damaged or unwanted proteins. - While chaperones can triage misfolded proteins for degradation, they do not directly perform the degradation themselves. *Protein Modification* - **Protein modification** involves the covalent attachment of chemical groups (e.g., phosphorylation, glycosylation) or other molecules to a protein. - This process is performed by specific enzymes like kinases or glycosyltransferases; chaperones’ role is more structural than enzymatic modification.

Q: Tyrosinemia Type I is caused due to deficiency of which enzyme?

Fumarylacetoacetate hydrolase. ***Fumarylacetoacetate hydrolase*** - **Tyrosinemia Type I**, also known as **hereditary tyrosinemia type 1 (HT1)**, is an **autosomal recessive** metabolic disorder caused by a deficiency of the enzyme **fumarylacetoacetate hydrolase (FAH)**. - This enzyme is crucial for the final step in the **tyrosine degradation pathway**, leading to the accumulation of toxic metabolites like fumarylacetoacetate and succinylacetone. *Tyrosine aminotransferase* - Deficiency of **tyrosine aminotransferase** causes **Tyrosinemia Type II**, a distinct disorder from Type I. - Type II tyrosinemia primarily affects the eyes and skin, presenting with **corneal ulcers** and painful **hyperkeratotic plaques**. *Homogentisate 1,2-dioxygenase* - Deficiency of **homogentisate 1,2-dioxygenase** leads to **alkaptonuria (black urine disease)**, a rare metabolic disorder. - This condition involves the accumulation of **homogentisic acid**, which causes dark urine, **ochronosis** (bluish-black pigmentation of connective tissues), and severe arthropathy. *4-hydroxyphenylpyruvate dioxygenase* - Deficiency of **4-hydroxyphenylpyruvate dioxygenase** results in **Tyrosinemia Type III**, another rare form of tyrosinemia. - This type is typically milder, often presenting with **neurological symptoms** such as intellectual disability and seizures, but without the severe liver and kidney damage seen in Type I.

Q: Which one of the following shows allosteric inhibition of glycolysis?

Citrate. ***Citrate*** - **Citrate** is a classic **allosteric inhibitor** of **phosphofructokinase-1 (PFK-1)**, the key regulatory enzyme in glycolysis - It binds to an allosteric site (distinct from the active site), reducing PFK-1's affinity for **fructose-6-phosphate** - This is a **negative feedback mechanism** - when citrate accumulates (indicating sufficient ATP production via the citric acid cycle), glycolysis slows down *Malonic acid* - **Malonic acid** is a **competitive inhibitor** (NOT allosteric) of succinate dehydrogenase in the citric acid cycle - It structurally resembles succinate and competes for the active site directly *2,3-BPG* - **2,3-Bisphosphoglycerate (2,3-BPG)** is an **allosteric effector** of hemoglobin (decreases oxygen affinity), not an enzyme inhibitor in glycolysis - It binds to hemoglobin, not to glycolytic enzymes *Amino acid alanine* - **Alanine** is an allosteric inhibitor of **pyruvate kinase** (not a glycolytic regulator in this context) - While it does show allosteric inhibition, it acts on gluconeogenesis regulation in the liver, not as a direct glycolytic inhibitor

Q: Galactosemia is due to deficiency of which enzyme?

Galactose-1-phosphate uridyltransferase. ***Galactose-1-phosphate uridyltransferase*** - Deficiency of **galactose-1-phosphate uridyltransferase (GALT)** leads to the most severe form, **classic galactosemia**. - This enzyme is crucial for converting **galactose-1-phosphate** to **glucose-1-phosphate** in the Leloir pathway. *HGPRT* - **HGPRT** (hypoxanthine-guanine phosphoribosyltransferase) deficiency causes **Lesch-Nyhan syndrome**, a distinct metabolic disorder. - Lesch-Nyhan syndrome is characterized by **hyperuricemia**, neurological dysfunction, and self-mutilation, unrelated to galactose metabolism. *Galactokinase* - Deficiency of **galactokinase** causes Type II galactosemia, a milder form than classic galactosemia. - This defect primarily leads to **cataracts** due to galactitol accumulation but does not result in the severe systemic issues seen in classic galactosemia. *Epimerase* - Deficiency of **UDP-galactose-4'-epimerase** (GALE) causes Type III galactosemia, which has a variable clinical presentation from mild to severe. - While involved in galactose metabolism, it's not the primary enzyme deficient in the most common and severe form of **galactosemia**.

Q: Phenylketonuria is due to deficiency of:

Phenylalanine hydroxylase (PAH). ***Phenylalanine hydroxylase (PAH)*** - **Phenylketonuria (PKU)** is an inherited metabolic disorder caused by a deficiency of the enzyme **phenylalanine hydroxylase (PAH)**. - This enzyme is crucial for converting the amino acid **phenylalanine** into **tyrosine**, and its deficiency leads to an accumulation of phenylalanine in the body. - PKU follows an **autosomal recessive** inheritance pattern. *Phenylalanine (amino acid)* - While **phenylalanine** accumulates to toxic levels in PKU, it is the substrate, not the deficient component. - The disease stems from the body's inability to metabolize this amino acid due to the enzyme deficiency. *Tyrosine* - **Tyrosine** is the product of the reaction catalyzed by PAH, and its production is limited in PKU. - However, the deficiency of tyrosine is a secondary effect, not the primary cause of PKU. *None of the options* - This option is incorrect because the deficiency of **phenylalanine hydroxylase (PAH)** is precisely the cause of Phenylketonuria.

Q: Fish odor syndrome is caused by deficiency of which enzyme?

Flavin-containing monooxygenase 3 (FMO3). ***Flavin-containing monooxygenase 3 (FMO3)*** - **Trimethylaminuria**, or "fish odor syndrome," is caused by a genetic defect in the **FMO3 enzyme**. - This enzyme is responsible for converting **trimethylamine (TMA)**, a breakdown product of certain foods, into an odorless form, **trimethylamine N-oxide (TMAO)**. *Fumarylacetoacetate hydrolase* - Deficiency in this enzyme causes **Tyrosinemia type 1**, a metabolic disorder affecting tyrosine metabolism. - It leads to severe liver disease, kidney dysfunction, and neurological crises, not a fishy body odor. *Methane monooxygenase* - This enzyme is found in certain **bacteria** (methanotrophs) and is involved in the metabolism of methane. - It is not present in humans and has no known link to human metabolic disorders like fish odor syndrome. *D-amino acid oxidase* - This enzyme is involved in the metabolism of **D-amino acids**, which are less common in mammals but found in bacteria and some foods. - Its deficiency is not associated with trimethylaminuria or a fishy body odor.

Q: The enzyme deficient in Galactosemia is:-

Galactose-1-phosphate uridyltransferase (GALT). ***Galactose-1-phosphate uridyltransferase (GALT)*** - Deficiency of **GALT** leads to the accumulation of **galactose-1-phosphate** in tissues, which is toxic and causes the symptoms of **classical galactosemia**. - This enzyme is crucial for the second step in the Leloir pathway, converting **galactose-1-phosphate** and UDP-glucose into UDP-galactose and glucose-1-phosphate. *Sphingomyelinase (associated with Niemann-Pick disease)* - Deficiency in **sphingomyelinase** causes the accumulation of **sphingomyelin**, leading to **Niemann-Pick disease**, characterized by hepatosplenomegaly and neurological deterioration. - This enzyme is involved in the catabolism of lipids, distinct from carbohydrate metabolism. *Glucocerebrosidase (associated with Gaucher's disease)* - Deficiency of **glucocerebrosidase** results in the accumulation of **glucocerebroside**, leading to **Gaucher's disease**, which affects the spleen, liver, bone marrow, and sometimes the brain. - This is a lysosomal storage disorder involving glycosphingolipids, not galactose metabolism. *Hexosaminidase (associated with Tay-Sachs disease)* - Deficiency of **hexosaminidase A** causes the accumulation of **GM2 ganglioside**, resulting in **Tay-Sachs disease**, a severe neurodegenerative disorder. - This enzyme primarily functions in the breakdown of gangliosides, which are complex lipids, not galactose.

Q: Serotonin is also known as?

5-hydroxytryptamine (5-HT). ***5-hydroxytryptamine (5-HT)*** - **Serotonin** is the common name for the neurotransmitter **5-hydroxytryptamine (5-HT)**. - This chemical name reflects its structure, derived from tryptophan, indicating a **hydroxyl group** at the 5-position of the **indole ring** and an **ethylamine side chain**. *3-Methoxytyramine* - **3-Methoxytyramine** is a metabolite of **dopamine**, not serotonin. - It is formed by the action of **catechol-O-methyltransferase (COMT)** on dopamine. *Phenethylamine* - **Phenethylamine** is a naturally occurring trace amine that acts as a **neuromodulator** or neurotransmitter. - It is structurally similar to certain recreational drugs but is not serotonin. *N-methyl phenylamine* - **N-methyl phenylamine** or N-methylaniline is an **organic chemical** used in dyes and other industrial applications. - It is not a neurotransmitter and has no relation to serotonin.

Question 1

What do chaperones assist in?

Accepted Answer

Protein Folding

Answer

Protein Cleavage

Answer

Protein Degradation

Answer

Protein Modification

Question 2

Tyrosinemia Type I is caused due to deficiency of which enzyme?

Accepted Answer

Fumarylacetoacetate hydrolase

Answer

Homogentisate 1,2-dioxygenase

Answer

Tyrosine aminotransferase

Answer

4-hydroxyphenylpyruvate dioxygenase

Question 3

Which one of the following shows allosteric inhibition of glycolysis?

Accepted Answer

Citrate

Answer

Amino acid alanine

Answer

2,3 BPG

Answer

Malonic acid

Question 4

Which of the following statements about vitamin K is correct?

Accepted Answer

Prolonged use of antimicrobials can lead to vitamin K deficiency

Answer

All of the options are true

Answer

Vitamin K acts as an anticoagulant

Answer

The recommended dietary allowance for vitamin K is 200-300 micrograms per day

Question 5

Galactosemia is due to deficiency of which enzyme?

Accepted Answer

Galactose-1-phosphate uridyltransferase

Answer

HGPRT

Answer

Galactokinase

Answer

Epimerase

Question 6

Phenylketonuria is due to deficiency of:

Accepted Answer

Phenylalanine hydroxylase (PAH)

Answer

Phenylalanine (amino acid)

Answer

Tyrosine

Answer

None of the options

Question 7

Fish odor syndrome is caused by deficiency of which enzyme?

Accepted Answer

Flavin-containing monooxygenase 3 (FMO3)

Answer

Fumarylacetoacetate hydrolase

Answer

Methane monooxygenase

Answer

D-amino acid oxidase

Question 8

True statement about vitamin K is?

Accepted Answer

Vitamin K affects bone health by activating proteins that bind calcium

Answer

Vitamin K is needed for action of clotting factor 8

Answer

Vitamin K deficiency leads to DVT

Answer

Vitamin K is water soluble

Question 9

The enzyme deficient in Galactosemia is:-

Accepted Answer

Galactose-1-phosphate uridyltransferase (GALT)

Answer

Sphingomyelinase

Answer

Glucocerebrosidase

Answer

Hexosaminidase

Question 10

Serotonin is also known as?

Accepted Answer

5-hydroxytryptamine (5-HT)

Answer

3-Methoxytyramine

Answer

Phenethylamine

Answer

N-methyl phenylamine

NEET-PG 2018 — Biochemistry