Tag: Metabolism of Triacylglycerol

Metabolism of Triacylglycerol

Metabolism of triacylglycerides

Q. 1

In the liver cells, triglycerides are formed primarily in the following organelle:

 A

Rough endoplasmic reticulum

 B

Smooth endoplasmic reticulum

 C

Golgi apparatus

 D

Ribosomes

Q. 1

In the liver cells, triglycerides are formed primarily in the following organelle:

 A

Rough endoplasmic reticulum

 B

Smooth endoplasmic reticulum

 C

Golgi apparatus

 D

Ribosomes

Ans. B

Explanation:

Synthesis of triacylglycerols mainly takes place on the smooth endoplasmic reticulum of the liver but can also be generated in adipose cells.

 
Regardless of the location of synthesis, the starting molecule is glycerol-3-phosphate produced in liver from glycerol stores or in adipose cells from dihydroxyacetone phosphate, the product of the fourth step of glycolysis.
 
Ref: Janson L.W., Tischler M.E. (2012). Chapter 7. Lipid Metabolism. In L.W. Janson, M.E. Tischler (Eds), The Big Picture: Medical Biochemistry.

 


Q. 2

A 32-year-old woman who has been on oral contraceptive pills for 5 years, developed symptoms of depression, irritability, nervousness and mental confusion. Her hemoglobin level was 8g/dl. Biochemical investigations revealed that she was excreting highly elevated concentrations of xanthurenic acid in urine. She also showed high levels of triglycerides and cholesterol in serum. All of the above are most probably related to a vitamin B6 deficiency caused by prolonged oral contraceptive use except:

 A

Increased urinary xanthurenic acid excretion

 B

Neurological symptoms by decreased synthesis of biogenic amines

 C

Decreased hemoglobin level

 D

Increased triglyceride and cholesterol levels

Q. 2

A 32-year-old woman who has been on oral contraceptive pills for 5 years, developed symptoms of depression, irritability, nervousness and mental confusion. Her hemoglobin level was 8g/dl. Biochemical investigations revealed that she was excreting highly elevated concentrations of xanthurenic acid in urine. She also showed high levels of triglycerides and cholesterol in serum. All of the above are most probably related to a vitamin B6 deficiency caused by prolonged oral contraceptive use except:

 A

Increased urinary xanthurenic acid excretion

 B

Neurological symptoms by decreased synthesis of biogenic amines

 C

Decreased hemoglobin level

 D

Increased triglyceride and cholesterol levels

Ans. D

Explanation:

Vit B6 deficiency will not cause increased triglyceride and cholesterol levels in serum.

It is best attributed to the metabolic effects of steroidal contraceptives.

Pyridoxal phosphate is a coenzyme involved in the metabolism of protein, carbohydrates and fat. In protein metabolism, Vit B6 participates in the decarboxylation of amino acids and the conversion of tryptophan to niacin or serotonin.

Ref: Harper’s Biochemistry Pages 258, 491 ; Textbook of Therapeutics: Drug and Disease Management By Richard A. Helms, David J. Quan, 2006, Page 737 ; Psychology and Schizophrenia By Janet E. Pletson, 2007, Page 110


Q. 3

Not true about eukaryotic gene:

 A

Polycistronic mRNA

 B

Noncoding intron

 C

Contain nuclear gene & pseudogene

 D

Modification of mRNA before transportation from nucleus

Q. 3

Not true about eukaryotic gene:

 A

Polycistronic mRNA

 B

Noncoding intron

 C

Contain nuclear gene & pseudogene

 D

Modification of mRNA before transportation from nucleus

Ans. A

Explanation:

A i.e. Polycistronic mRNA

Quiz In Between


Q. 4

Triglycerides synthesis is increased by:    

 A

Growth hormone

 B

Insulin

 C

Cortisol

 D

Glucagons

Q. 4

Triglycerides synthesis is increased by:    

 A

Growth hormone

 B

Insulin

 C

Cortisol

 D

Glucagons

Ans. B

Explanation:

Q. 5

Where is the triglycerides stored in the human body?

 A

Nerve cells

 B

Adipose tissues

 C

Both 

 D

None

Q. 5

Where is the triglycerides stored in the human body?

 A

Nerve cells

 B

Adipose tissues

 C

Both 

 D

None

Ans. B

Explanation:

Triglycerides are stored in adipose tissues.

Quiz In Between



Metabolism of Triacylglycerol

Metabolism of Triacylglycerol


METABOLISM OF TRIACYLGLYCEROL

  • Triacylglycerol contains one molecule of glycerol and 3 molecules of fatty acid.
  • Occurs in liver, adipose tissue, intestinal mucosal cells.
  • Organelle- endoplasmic reticulum.

3 steps-

  1. Fatty acid to acyl CoA by Acyl CoA synthase (thiokinase)
  2. Glycerol to glycerol-3-phosphate (formed from glucose-3- phosphate dehydrogenase in adipose tissue) by glucose kinase.
  3. Phosphatidate undergoes hydrolytic dephosphorylation which is esterified to form triacylglycerol.
  • In adipose tissues- insulin enhances triacylglycerol synthesis.
  • In Diabetes, glycerol-3-phosphate is hampered leading to decrease triglyceride synthesis.
  • Triglyceride is the major lipid for adipose tissues.

Triacylglycerol hydrolysis (lipolysis)-

  • Triacylglycerol (stored fat) is degraded.
  • Enzyme- hormone sensitive lipase.
  • Lipolysis refers to hydrolysis of triacylglycerol in adipose tissues.

Regulation of lipolysis-

  1. Hormone sensitive lipase activated by-
  2. Epinephrine
  3. Catecholamines
  4. Thyroid hormones
  5. Growth hormone
  6. ACTH
  7. Glucocorticoids

Hormone sensitive lipase inactivated by-

  1. Insulin
  2. Prostaglandin

Exam Important

  • Triacylglycerol contains one molecule of glycerol and 3 molecules of fatty acid.
  • Occurs in liver, adipose tissue, intestinal mucosal cells.
  • Organelle- endoplasmic reticulum.

3 steps-

  1. Fatty acid to acyl CoA by Acyl CoA synthase (thiokinase)
  2. Glycerol to glycerol-3-phosphate (formed from glucose-3- phosphate dehydrogenase in adipose tissue) by glucose kinase.
  3. Phosphatidate undergoes hydrolytic dephosphorylation which is esterified to form triacylglycerol.
  • In adipose tissues- insulin enhances triacylglycerol synthesis.
  • In Diabetes, glycerol-3-phosphate is hampered leading to decrease triglyceride synthesis.
  • Triglyceride is the major lipid for adipose tissues.
  • Triacylglycerol hydrolysis (lipolysis)-
  • Triacylglycerol (stored fat) is degraded.
  • Enzyme- hormone sensitive lipase.
  • Lipolysis refers to hydrolysis of triacylglycerol in adipose tissues.

Regulation of lipolysis-

Hormone sensitive lipase activated by-

  1. Epinephrine
  2. Catecholamines
  3. Thyroid hormones
  4. Growth hormone
  5. ACTH
  6. Glucocorticoids

Hormone sensitive lipase inactivated by-

  1. Insulin
  2. Prostaglandin
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