Triacylglycerol are ester of fatty acids and have glycerol as alcohol. Fatty acids which are either synthesized by the endogenous substances or is taken through diet are stored in adipose tissue as triacylglycerol or neutral fats. It is known as body’s major fuel storage reserve.

Triacylglycerol are highly concentrated energy stores more than glycogen because they are more reduced (having more hydrogen atom) and anhydrous (non-polar).

Location: biosynthesis of triacylglycerol occurs in both liver and adipose tissue from glycerol-3-phosphate as starting compound.

1. In liver, glycerol-3-phosphate is produced from phosphorylation of glycerol by glycerol kinase enzyme
2. Adipose tissue lacks glycerol kinase enzyme that’s why, glycerol-3-phosphate is produced by glucose via DHAP

Reactions of synthesis of triacylglycerol

• Firstly, fatty acids are activated to acyl-CoA.
• 2 more molecules of acyl-CoA combines with glycerol-3-phosphate and form phosphatidic acid (1,2-diacylglycerol phosphate) through the formation of lysophosphatidic acid.
• Dephosphorylation of phosphatidic acid produces diacylglycerol
• esterification of another molecule of acyl-CoA with diacylglycerol leads to the formation of triacylglycerol.

Multiple choice questions (MCQs)

1. What is the other name of triacylglycerol?
   A. waxes B. phospholipids
   C. neutral fats D. all of the above
2. Which type of alcohol is present in triacylglycerol?
   A. sphingosine B. glycerol
   C. methanol D. none of the above
3. Which is the site of synthesis of triacylglycerol?
   A. liver B. areolar tissue
   C. adipose tissue D. both A and C
4. Out of glycogen and triacylglycerol which one is more efficient energy store?
   A. glycogen B. triacylglycerol
   C. both D. none
5. Match the following enzymes with the product it form-
   a. glycerol kinase 1. Phosphatidic acid
   b. acyl transferase 2. diacylglycerol
   C. phosphohydrolase 3. Lysophosphatidic acid
   d. acyl transferase 4. Glycerol-3-phosphate
6. How is glycerol-3-phosphate formed in liver?
   A. via DHAP B. NADPH
   C. glycerol kinase enzyme D. both B and C
7. How is glycerol-3-phosphate formed in adipose tissue?
   A. via DHAP B. NADPH
   C. glycerol kinase enzyme D. both B and C
8. Which of the following statement is NOT true?
   A. firstly diacylglycerol is formed and than triacylglycerol
   B. triacylglycerol are non polar in nature
   C. fatty acids are the backbone of triacylglycerol
   D. triacylglycerol is formed from both exogenous and endogenous substances
9. What is the full form of DHAP?
   A. Dihydroxyacetone phosphate
   B. dihydrogen acetone phosphate
   C. Dihydroxyacetone phosphatase
   D. Dishydroxyacetone phosphate
10. What is the active form of fatty acids?
    A. acyl-C B. acetyl-CoA
    C. alkyl-CoA D. none of the above
11. Which of the following enzyme participate in biosynthesis of triacylglycerol?
    A. glycerol kinase B. acyl transferase
    C. phosphohydrolase D. all of the above
12. Why is triacylglycerol more concentrated energy store?
    A. it is less reduced and anhydrous B. more reduced and hydrous
    C. reduced and anhydrous D. none
13. How many fatty acids are present in triacylglycerol?
    A. 2 b. 3
    C. 4 D. 6
14. Which compound is termed as the backbone of triacylglycerol?
    A. glycerol B. fatty acids
    C. esters D. all of the above

ANSWERS:-

1. neutral fats

2. glycerol

3. both A and C

4. triacylglycerol

5. a – 4 b – 3 c – 2 d – 1

6. glycerol kinase enzyme

7. via DHAP

8. fatty acids are the backbone of triacylglycerol

9. dihydroxyacetone phosphate

10. none of the above

11. all of the above

12. reduced and anhydrous

13. 3

14. glycerol

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REFERENCE:- Pankaja Naik- Biochemistry; 4^th edition; page no:- 230-233 .