L3: Fatty acids & simple lipids

Question 1

What are lipids?

Answer 1

❖ Lipids are compounds that are relatively insoluble in water, but freely soluble in non-polar organic solvents like benzene, ether, and acetone, etc.

Question 2

What is the biological importance of lipids?

Answer 2

1) Storage form of energy (triglycerides).

2) Structural components of membranes (phospholipids and cholesterol).

3) Metabolic regulators (e.g. steroid hormones).

4) Help in the absorption of fat-soluble vitamins (A, D, E, and K).

5) Protect internal organs by providing a cushioning effect (pads of fat).

6) Provide insulation against changes in external temperature (subcutaneous fat).

7) Act as electric insulators in neurons.

Question 3

What are lipids classified into?

Answer 3

1) Simple lipids:
❖ They are formed of fatty acids and alcohol.
❖ They are further classified according to the type of alcohol present into:
 Fats and oils.  Waxes.

2) Compound lipids:
❖ They are formed of simple lipids and another non-lipid part.

3) Derived lipids:
❖ They are substances derived from simple lipids and compound lipids by hydrolysis.
❖ They also include substances related to lipids and associating lipids in nature.

Question 4

What is glycerol?

Answer 4

It is polyhydric alcohol containing 3 OH groups.

Question 5

What is the importance of glycerol?

Answer 5

It is used in pharmaceutical (e.g. glycerin suppositories) and cosmetic preparations.

It is used as a vasodilator agent in coronary heart disease in form of nitro-glycerine.

Question 6

fatty acids

Answer 6

❖ Fatty acids are usually monocarboxylic straight aliphatic chains with a methyl group at one end (called the ω-carbon) and a carboxyl group at the other end.
❖ It is the most common component of lipids in the body.
❖ They are generally found in ester linkage in different classes of lipids

Question 7

How are fatty acids numbered?

Answer 7

1) C-system numbering starts from the carboxyl-terminal:
2) ω-system numbering starts from the methyl end:

Question 8

How are fatty acids classified depending on the total number of carbon atoms in the chain?

Answer 8

Even chain:
 They have carbon atoms 2, 4, 6, and similar series.
 Most of the naturally-occurring lipids contain even chain fatty acids.

Odd chain:  They have carbon atoms 3, 5, 7, etc.

Question 9

How are fatty acids classified?

Answer 9

Acc. To total number of carbon atoms in the chain

Acc. To the length of the hydrocarbon chain

Acc. To the nature of the hydrocarbon chain

Question 10

How are fatty acids classified depending on the length of the chain?

Answer 10

-Short with 2 to 6 carbon atoms.
-medium with 8 to 14 carbon atoms.
-long with 16 to 22 carbon atoms.
-very long with more than22 carbon atoms.

Question 11

How are fatty acids classified according to the nature of the hydrocarbon chain?

Answer 11

❖ Saturated fatty acids.

❖ Unsaturated fatty acids:
May be sub-classified into:

Mono-unsaturated (mono-enoic)
 having a single double bond.

Polyunsaturated (poly-enoic)
 with 2 or more double bonds.

Question 12

What are examples of saturated fatty acids?

Answer 12

Acetic 2

Butyric 4

Caproic 5

Palmitic 16

Stearic 18

Propionic 3

Valeric 5

Question 13

What are the examples of monounsaturated fatty acids?

Answer 13

Palmitoleic (16: 1∆9, W7)

Oleic (18: 1∆9, W9)

Nervonic (24: 1∆15, W9)

Question 14

What are the common sources for mono-unsaturated fatty acids?

Answer 14

3S-2C-ON

❖ Common sources: Many vegetable oils: sunflower, olive, nuts, corn, sesame, soybean, and cod liver oils.

Question 15

What are the poly-unsaturated fatty acids (PUFA)?

Answer 15

❖ They are fatty acids that contain more than one double bond.
❖ They must be taken into the diet because the body cannot synthesize them as the enzymes
needed for their synthesis are absent in humans.

Question 16

What are the common sources for PUFA?

Answer 16

Many vegetable oils: sunflower, olive, nuts, corn, soybean, and cod liver oils.

Question 17

What is the Importance of essential fatty acids (PUFAs)?

Answer 17

 They are essential for growth.
 They are essential for phospholipid formation
 Important for prostaglandins biosynthesis.

Question 18

What are examples of PUFAs?

Answer 18

Linoleic (18: 2∆9,12, W6)
Linolenic (18: 3∆9,12,15, W3)
Arachidonic. (20: 4∆5,8,11,14, W6)

Question 19

What are simple lipids?

Answer 19

They are esters of fatty acids with various alcohols. The alcohol may be glycerol or other than glycerol.

Question 20

What are simple lipids classified into?

Answer 20

They are classified into fats, oils, and waxes, according to the type of alcohol they contain.

Question 21

What are the other names for fats and oils?

Answer 21

(triglycerides = triacylglycerol)

Question 22

What are triglycerides?

Answer 22

They are esters of fatty acids with glycerol.

The fatty acids may be the same forming simple triglycerides e.g. palmitic or stearic
acids forming tripalmitate or tristearate respectively, or they may be different forming mixed triglycerides with 3 different fatty acids.

Question 23

Why are triglycerides called by this name?

Answer 23

because they are triesters formed of glycerol and 3 fatty acids

Question 24

What is the function of triglycerides?

Answer 24

1) Storage of energy as fat:
 The triacylglycerols are the storage form of lipids in the adipose tissue.

2) Provide essential fatty acids.

3) Carriers of fat-soluble vitamins (A-D-E-K).

Question 25

What are waxes?

Answer 25

They are esters of fatty acids with a long-chain monohydric alcohol.

Question 26

What are examples of waxes?

Answer 26

-The most commonly known animal wax is beeswax
-One of the most important waxes in plasma and tissues is cholesterol esters (cholesterol wax).
-Cerumen (earwax) from the ceruminous glands in ears.