Lipid Metabolism Practice Questions

Q: Which of the following is a transfatty acid?

Elaidic acid. ***Elaidic acid*** - **Elaidic acid** is a common **trans-fatty acid** found in partially hydrogenated vegetable oils. - Its chemical structure includes a **trans double bond**, which gives it properties distinct from cis-fatty acids. *Oleic acid* - **Oleic acid** is a **monounsaturated fatty acid** commonly found in olive oil and other plant fats. - It has a **cis double bond**, which causes a bend in its molecular structure. *Stearic acid* - **Stearic acid** is a **saturated fatty acid** with no double bonds in its carbon chain. - It is found in animal fats and some plant oils, and its straight chain allows for tight packing. *Arachidonic acid* - **Arachidonic acid** is a **polyunsaturated omega-6 fatty acid** with multiple cis double bonds. - It is involved in inflammation and is a precursor to eicosanoids.

Q: Which of the following is not an essential fatty acid?

Palmitic acid. ***Palmitic acid*** - **Palmitic acid** is a **saturated fatty acid** that can be synthesized by the human body and is therefore not considered essential. - It is one of the most common fatty acids in animals and plants and is a major component of membrane lipids. *Linoleic acid* - **Linoleic acid** (an **omega-6 fatty acid**) is an essential fatty acid because the human body cannot synthesize it and it must be obtained from the diet. - It serves as a precursor for other fatty acids, including **arachidonic acid**. *Linolenic acid* - **Linolenic acid** (an **omega-3 fatty acid**) is an essential fatty acid that the human body cannot produce. - It is critical for cell membrane structure and as a precursor for other important fatty acids like **EPA** and **DHA**. *Arachidonic acid* - While important for various biological processes, **arachidonic acid** can be synthesized in the body from the essential fatty acid **linoleic acid**. - Therefore, it is considered conditionally essential, as its essentiality depends on adequate intake of its precursor.

Q: All are true about beta oxidation of fatty acids except which of the following?

Carnitine Acyl transferase I is stimulated by malonyl CoA. ***Carnitine Acyl transferase I is stimulated by malonyl CoA*** - Malonyl CoA is a key intermediate in **fatty acid synthesis** and acts as an **inhibitor** of carnitine acyltransferase I (CAT1), not a stimulator. - This inhibition ensures that when fatty acid synthesis is active, fatty acid oxidation is suppressed, preventing a futile cycle. *Carnitine acyl transferase I is the rate limiting enzyme of fatty acid oxidation* - **Carnitine palmitoyltransferase 1 (CPT1)**, also known as carnitine acyltransferase I, is indeed the **rate-limiting step** for long-chain fatty acid entry into the mitochondrial matrix for beta-oxidation. - This enzyme controls the transport of fatty acyl-CoA into the mitochondria, which is essential for its subsequent breakdown. *Carnitine acyl transferase I is inhibited by malonyl CoA.* - **Malonyl CoA**, a precursor in fatty acid synthesis, serves as an allosteric inhibitor of **CAT1**. - This mechanism ensures that when the cell is actively synthesizing fatty acids, it simultaneously prevents their breakdown, helping to regulate overall energy metabolism. *Carnitine Acyl transferase I defect causes a decrease in acylcarnitine levels* - A defect in **CAT1** means fatty acids cannot be efficiently transported into the mitochondria to be converted into acylcarnitine for transport. - This leads to an accumulation of **free fatty acids** in the cytoplasm and a **decrease in acylcarnitine levels** in the blood and tissues, which can be used diagnostically.

Q: X-linked adrenoleukodystrophy is a type of:

Fatty acid disorder. ***Fatty acid disorder*** - **X-linked adrenoleukodystrophy (X-ALD)** is characterized by impaired peroxisomal beta-oxidation of **very long-chain fatty acids (VLCFAs)**, leading to their accumulation. - This accumulation primarily affects the **adrenal glands** and **nervous system**, causing progressive demyelination and adrenal insufficiency. *Lysosomal storage disorder* - **Lysosomal storage disorders** involve defects in lysosomal enzymes, leading to the accumulation of specific substrates within lysosomes. - While X-ALD involves fat metabolism, the affected organelles are **peroxisomes**, not lysosomes. *Mucopolysaccharidoses* - **Mucopolysaccharidoses (MPS)** are a group of lysosomal storage disorders characterized by the defective breakdown of **glycosaminoglycans (GAGs)**, also known as mucopolysaccharides. - These disorders present with skeletal abnormalities, intellectual disability, and organomegaly, which are distinct from the primary pathology of X-ALD. *Glycogen defect disorder* - **Glycogen defect disorders** (or glycogen storage diseases) result from mutations in enzymes involved in **glycogen synthesis or breakdown**. - These conditions primarily affect carbohydrate metabolism and can lead to symptoms like hypoglycemia, muscle weakness, and hepatomegaly, distinct from the fatty acid metabolism defect in X-ALD.

Q: Refsum's disease is due to deficiency of which of the following enzyme?

Phytanic alpha oxidase. ***Phytanic alpha oxidase*** - **Refsum's disease** is an **autosomal recessive peroxisomal disorder** characterized by the accumulation of **phytanic acid**. - This accumulation occurs due to the deficiency of **phytanic acid alpha-oxidase**, an enzyme crucial for the **alpha-oxidation** of branched-chain fatty acids. *Malonate dehydrogenase* - This enzyme is involved in the metabolism of **malonate**, typically oxidizing it to **malonyl-CoA**. - Its deficiency is not associated with Refsum's disease or the accumulation of phytanic acid. *Thiophorase* - Also known as **succinyl-CoA:3-ketoacid CoA transferase**, thiophorase is involved in **ketone body metabolism**. - Its deficiency leads to **succinyl-CoA:3-ketoacid CoA transferase deficiency**, causing **ketoacidosis**, not Refsum's disease. *Succinate thiokinase* - Also known as **succinyl-CoA synthetase**, this enzyme plays a role in the **Krebs cycle**, converting **succinyl-CoA to succinate**. - Its deficiency is a rare metabolic disorder presenting with **encephalopathy and lactic acidosis**, unrelated to phytanic acid metabolism.

Q: In congenital adrenal hyperplasia, which enzyme deficiency is primarily responsible for precocious puberty in males?

21-hydroxylase deficiency. ***21-hydroxylase deficiency*** - This is the **most common form** of congenital adrenal hyperplasia (CAH) and leads to a **deficiency in cortisol and aldosterone** production [1]. - The accumulation of precursors shunts metabolic pathways towards **androgen production**, causing precocious puberty in males due to **excessive adrenal androgens** [1]. *11-beta-hydroxylase deficiency* - This deficiency also leads to **decreased cortisol** and an accumulation of precursors, but it specifically causes an increase in **deoxycorticosterone (DOC)**, which has mineralocorticoid activity. - While it also causes **androgen excess** (leading to precocious puberty in males), it is **less common** than 21-hydroxylase deficiency as the primary cause. *Both* - While both deficiencies can cause androgen excess and precocious puberty, **21-hydroxylase deficiency** is by far the more frequent and significant cause of these symptoms in CAH. - Attributing it equally to both would overlook the **prevalence** and primary impact of 21-hydroxylase deficiency. *Neither* - This option is incorrect because both 21-hydroxylase deficiency and 11-beta-hydroxylase deficiency can lead to **androgen excess**, which is the underlying cause of precocious puberty in CAH. - The condition is characterized by a defect in steroid synthesis, which inevitably results in a **hormonal imbalance**.

Q: Aromatase produces estrogen from -

Androgen. ***Androgen*** - **Aromatase** is an enzyme complex that converts **androgens** (specifically androstenedione and testosterone) into **estrogens** (estrone and estradiol, respectively). - This conversion is a key step in **estrogen biosynthesis** and occurs in various tissues, including the ovaries, placenta, brain, and adipose tissue. *Progesterone* - **Progesterone** is a precursor to androgens, but it is not directly converted to estrogen by aromatase. - It plays a primary role in the **menstrual cycle** and **pregnancy**. *Cortisol* - **Cortisol** is a **glucocorticoid hormone** produced in the adrenal cortex and is not a substrate for aromatase. - Its primary functions relate to stress response, metabolism, and immune regulation. *Aldosterone* - **Aldosterone** is a **mineralocorticoid hormone** produced in the adrenal cortex and is not involved in estrogen synthesis. - It primarily regulates **blood pressure** and electrolyte balance.

Q: A child presents with bone pain and hepatosplenomegaly, indicative of Gaucher's disease. A trephine biopsy and aspirate show the following finding. Which of the following is the most likely enzyme deficient in this condition?

Glucocerebrosidase. ***Correct: Glucocerebrosidase*** - The clinical presentation of **bone pain**, **hepatosplenomegaly**, and the characteristic histological finding of **lipid-laden macrophages** (Gaucher cells) with a **crinkled paper** appearance in the bone marrow aspirate are highly suggestive of **Gaucher's disease**. - **Gaucher's disease** is caused by a deficiency of the lysosomal enzyme **glucocerebrosidase**, leading to the accumulation of **glucocerebroside**. *Incorrect: Hexosaminidase* - Deficiency of **hexosaminidase A** is associated with **Tay-Sachs disease**, which presents with neurological degeneration but typically **lacks hepatosplenomegaly** and bone pain. - The histological findings in Tay-Sachs disease would show neuronal storage of **GM2 gangliosides**, not Gaucher cells. *Incorrect: Sphingomyelinase* - Deficiency of **sphingomyelinase** causes **Niemann-Pick disease**, characterized by hepatosplenomegaly, neurological involvement, and interstitial lung disease, but the storage cells (foam cells) have a **foamy appearance** due to sphingomyelin accumulation, not the "crinkled paper" appearance of Gaucher cells. - While there is organomegaly, the distinct **histological features** in the image rule out Niemann-Pick disease. *Incorrect: Alpha 1,4-glucosidase* - Deficiency of **alpha 1,4-glucosidase** (acid maltase) causes **Pompe disease** (Glycogen Storage Disease Type II), which primarily affects muscle and liver with **glycogen accumulation**. - Pompe disease does not typically present with the same type of **bone pain** or the characteristic **Gaucher cells** seen in the image.

Question 1

Which of the following is a transfatty acid?

Accepted Answer

Elaidic acid

Answer

Oleic acid

Answer

Stearic acid

Answer

Arachidonic acid

Question 2

Which of the following is not an essential fatty acid?

Accepted Answer

Palmitic acid

Answer

Linolenic acid

Answer

Linoleic acid

Answer

Arachidonic acid

Question 3

Which of the following statements about reverse cholesterol transport is false?

Accepted Answer

Lecithin Cholesterol Acyl Transferase helps in the conversion of Spheroidal HDL to Discoidal HDL.

Answer

Transport of cholesterol from extrahepatic tissues to liver.

Answer

Cholesterol Ester Transfer Protein reduces HDL levels.

Answer

ATP Binding Cassette Transporter protein is involved in the conversion of HDL3 to HDL2.

Question 4

All are true about beta oxidation of fatty acids except which of the following?

Accepted Answer

Carnitine Acyl transferase I is stimulated by malonyl CoA

Answer

Carnitine Acyl transferase I defect causes a decrease in acylcarnitine levels

Answer

Carnitine acyl transferase I is the rate limiting enzyme of fatty acid oxidation

Answer

Carnitine acyl transferase I is inhibited by malonyl CoA

Question 5

Which of the following statements about beta oxidation of fatty acids is correct?

Accepted Answer

Fatty acid oxidation defects can lead to hypoglycemia.

Answer

Ketone bodies are formed by complete oxidation of fatty acids during starvation.

Answer

Odd chain fatty acid oxidation provides only propionyl CoA.

Answer

Stearic acid on oxidation provides 120 ATPs.

Question 6

X-linked adrenoleukodystrophy is a type of:

Accepted Answer

Fatty acid disorder

Answer

Lysosomal storage disorder

Answer

Glycogen defect disorder

Answer

Mucopolysaccharidoses

Question 7

Refsum's disease is due to deficiency of which of the following enzyme?

Accepted Answer

Phytanic alpha oxidase

Answer

Thiophorase

Answer

Succinate thiokinase

Answer

Malonate dehydrogenase

Question 8

In congenital adrenal hyperplasia, which enzyme deficiency is primarily responsible for precocious puberty in males?

Accepted Answer

21-hydroxylase deficiency

Answer

11-beta-hydroxylase deficiency

Answer

Both

Answer

Neither

Question 9

Aromatase produces estrogen from -

Accepted Answer

Androgen

Answer

Progesterone

Answer

Cortisol

Answer

Aldosterone

Question 10

A child presents with bone pain and hepatosplenomegaly, indicative of Gaucher's disease. A trephine biopsy and aspirate show the following finding. Which of the following is the most likely enzyme deficient in this condition?

Accepted Answer

Glucocerebrosidase

Answer

Hexosaminidase

Answer

Sphingomyelinase

Answer

Alpha 1,4-glucosidase

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

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