Solved Important Questions On LIPID Chemistry

Q. Which is the lipid that accumulates in Fabry's disease?

Ans: Globoside

Q. Enzymes which are defective in Fabry's disease?

Ans: a Galactosidase

Q. Beta Galactosidase defect causes all except

1. Morquio B disease
2. Krabbe's disease
3. GM1 Gangliosidosis
4. Gaucher's disease

Explanation

• Galactose has two isoforms, Galactose-I and Galactose-II.
• Galactose-I produces GM1 ganglioside.
• Galactose-II produces keratan sulfate (Morquio B disease) and myelin (Krabbe disease).

Q. What are the two nutritionally essential fatty acids?

Ans: Linoleic acid and Alpha linolenic acid

Explanation

• Linoleic acid
  • 18 carbons
  • ω6 type
• Alpha linolenic acid
  • 18 carbons
  • ω3 type
• These fatty acids are not synthesized by metabolic pathways
• We can synthesize only saturated fatty acids
• Unsaturated fatty acids are required to maintain membrane integrity
• Saturated fatty acids are synthesized and double bonds are introduced using human desaturase enzyme system
  • This enzyme removes hydrogen atoms at specific location and introduces double bonds
  • Human desaturase enzymes cannot desaturate beyond (delta symbol 9), meaning for a 18C fatty acid, its ω9 (so we can synthesize only ω9 fatty acids and not ω3 and ω6)
• 18-carbon linoleic acid (ω6) and alpha-linolenic acid (ω3) are essential in the diet because they have a chain elongation system that adds carbon atoms to the chain without affecting the omega numbering

Q. Glycolipids are derivatives of

Ans: Ceramide

Q. Nutritionally essential fatty acids are

Ans: Linoleic acids and a Linolenic acid

Q. Amphipathic lipids are

Ans: Phospholipids, Cholesterol

Q. Non-polar lipids are

Ans: Cholesterol ester, Triacylglycerol

Q. Lipid which accumulates in Gaucher's disease

Ans: Cerebroside

Q. Lipid which accumulates in Fabry's disease

Ans: Globoside

Q. Globosides accumulates in

Ans: Fabry's and Sandhoff diseases

Q. Hexosaminidase A defect causes,

1. Cerebrosidosis
2. GM3 Gangliosidosis
3. GM2 Gangliosidosis
4. GM1 Gangliosidosis

Explanation: Hexosaminidase A defect causes both Tay Sachs (GM2 gangliosidosis)

Q. Beta Galactosidase defect causes all except:

1. Krabbe's disease
2. GM3 Gangliosidosis
3. Morquio B disease
4. GM1 Gangliosidosis

Explanation:

• ? galactosidase defect causes
• GM1 gangliosidosis
• Morquio B disease
• Krabbe's disease

Q. All the following are true about cholesterol except:

1. Hydroxyl group at 3rd position
2. Methyl groups at 10, 13th positions
3. Side chain at 17 position
4. Has benzene ring

Explanation: Cholesterol has a phenanthrene ring.

Q. Which of the following is a neutral lipid?

1. Phospholipid
2. Monoacyl glycerol
3. Diacylglycerol
4. Cholesterol ester

Explanation

• Neutral lipids are nonpolar
• Glycerol has 3 hydroxyl groups
• Diacylglycerol is amphipathic
  • Two groups are attached to fatty acids
  • One group is polar
• Monocylglycerol is amphipathic
  • One group is attached to fatty acids
  • Two groups are polar

Q. Arachidonic acid is a fatty acid of which type?

1. 20, omega 6
2.  20, omega 3
3. 18, omega 6
4. 22, omega 3

Explanation

• 20, omega 3, is timnodonic acid
• 18, omega 6 is linoleic acids
• 22, omega 3 is cervonic acid (DHA)
• DHA (Docosahexaenoic acid)
  • 22 carbons
  • 6 double bonds
  • Omega 3 type
  • Essential for myelination
  • Supplements in children diet

Q. A 46-year-old male was referred for dermatological evaluation of purpura. He was already getting treated for proteinuria and a recent episode of MI. Clinical biochemists suspected Fabry's disease. The lipid which accumulates in Fabry's disease is?

1. Cerebroside
2. Globoside
3. Ganglioside
4. Ceramide

Explanation

• Triad of Fabry's disease:
  • Angiokeratoma, reddish color lesions
  • Proteinuria
  • Early onset MI or accelerated atherosclerosis

Q. For the first few months, an eight-month-old child's growth and development were normal, then symptoms such as deafness, blindness, atrophied muscle, inability to swallow, and convulsions began to appear. During the fundus inspection, a cherry red macula was also seen in both eyes. Suspecting sphingolipidosis, the physician tested for globosides and gangliosides levels and found that both were increased. Based on this finding, what is the most accurate diagnosis for this patient?

1. Sandhoff disease
2. Tay Sachs disease
3. Gaucher's disease
4. Fabry's disease

Explanation

Sandhoff disease:

• Neurological manifestations:
  • Deafness
  • Blindness
  • Atrophied muscle
  • Inability to swallow
  • Convulsions
• Cherry red appearance with elevated globoside and gangliosides
• Elevated globoside and gangliosides–Sandhoff disease

Q. Identify the structure provided above

1. Cerebroside
2. Globoside
3. GM1 Ganglioside
4. GM2 Ganglioside

Q. Which of the following is not a lipid?

1. Glycerol
2. Palmitic acid
3. Triacylglycerol
4. Cholesterol

Explanation

• Glycerol with 3 OH group is a carbohydrate
• Palmitic acid is a fatty acid (precursor lipid)
• Triacylglycerol is a simple lipid (fat)
• Cholesterol is a derived lipid

Q. All of the following are components of triacylglycerol except?

1. Glycerol
2. Palmitic acid
3. Sphingosine
4. Stearic acid

Explanation: Sphingosine is wax

Q. Which of the following is a wax?

1. Triacylglycerol
2. Ceramide
3. Sphingomyelin
4. Lecithin

Explanation

• Wax is a simple lipid with high molecular weight alcohol (like sphingosine)
• Ceramide is composed of sphingosine and fatty acids

Q. Which of the following is a derived lipid?

1. Triacylglycerol
2. Fatty acid
3. Sphingomyelin
4. Cholesterol

Q. All of the following are components of sphingomyelin except?

1. Sphingosine
2. Fatty acid
3. Choline
4. Ethanolamine

Explanation

• Sphingosine + fatty acid - ceramide.
• OH group of ceramide binds with phosphate group.
• Phosphate binds with choline - forms Sphingomyelin. Phosphatidyl ethanolamine is cephaline.
• Phosphatidyl ethanolamine is cephaline

Q. A premature child presence with infant respiratory distress syndrome. The neonatologist says the neonate is yet to produce lecithin adequately. All of the following are components of Lecithin except?

1. Glycerol
2. Choline
3. Phosphatidate
4. Ceramide

Explanation

• Glycerol - has 3 OH groups.
• In a surfactant  2 OH groups should attach to 2 fatty acids.
  • The fatty acid is dipalmitoyl phosphatidyl choline.
• 3rd OH attached to the phosphate group.
  • Phosphate then binds to choline.
• This structure is now called dipalmitoyl phosphatidyl choline.
• Therefore, there are glycerol, palmitic acid, phosphate group and choline.
• Ceramide is a component of sphingomyelin.

Q. Viper venom has phospholipase A2. Identify the site of Phospholipase A2 activity in the given image

1. A
2. B
3. X
4. Y

Explanation

• A, B, X, Y in the image are the sites where various enzymes can act.
• Various enzymes are:
  • Phospholipase A1
  • Phospholipase A2 (present in viper's venom and in bee sting)
  • Phospholipase B
  • Phospholipase C
  • Phospholipase D

Q. Products on the enzyme X are:

1. Lysophospholipid and fatty acid
2. Inositol trisphosphate and diacylglycerol
3. Phosphatidic acid and a nitrogenous base
4. Inositol triphosphate and phosphatidic acid

Explanation

• Enzymes X acts before the phosphate group of the 3rd carbon atom.
• Enzyme X is phospholipase C.
• The products formed are inositol trisphosphate (IP3) and diacylglycerol (DAG).

Important points to remember

• Sphingosine combines with fatty acids to form ceramide
• Amino acid precursor of sphingosine is serine
• Phosphatidylcholine is lecithin
• Phosphatidyl ethanolamine is cephaline
• Diphosphatidyl glycerol is cardiolipin

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