Lipids II: TAGs and Phospholipids

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Questions and Answers

What primarily causes rancidity in fats and oils?

Presence of antioxidants

High temperatures only

Exposure to air, moisture, and light (correct)

High concentrations of saturated fatty acids

Which type of lipid is characterized as being amphipathic?

Cholesterol

Phospholipids (correct)

Triglycerides

Saturated fats

What is the main composition of dipalmitoyllecithin?

Fatty acids, glycerol, and phosphoric acid (correct)

Glycerol, fatty acids, and carbohydrates

Fatty acids and amino acids

Fatty acids and cholesterol

Which type of lipids are the most abundant in the cell membrane?

Phospholipids Signup and view all the answers

What is the role of sphingomyelins in the body?

Structural components of nerve cell membranes Signup and view all the answers

Which of the following lipids do NOT contain sugar?

Sphingomyelins Signup and view all the answers

What substance is crucial for normal lung function and is found in large amounts in alveoli?

Lecithin Signup and view all the answers

Glycolipids are especially important in which type of tissue?

Nervous tissue Signup and view all the answers

Which fatty acid is typically attached to the β-carbon in lecithin?

Polyunsaturated fatty acid Signup and view all the answers

What functional role do antioxidants play in relation to rancidity?

They prevent the oxidation of fats Signup and view all the answers

What are triacylglycerols primarily known for in the body?

Acting as the storage form of lipids in adipose tissue Signup and view all the answers

What occurs during the hydrolysis of triacylglycerols?

Triacylglycerols are converted into free fatty acids and glycerol. Signup and view all the answers

Which of the following describes the saponification process?

The hydrolysis of triacylglycerols by alkali to produce soap. Signup and view all the answers

How does the physical state of triacylglycerols at room temperature vary?

They are liquid if composed of short and medium-chain fatty acids with high unsaturation. Signup and view all the answers

What is one main function of glycolipids in the body?

They are integral components of membrane structure. Signup and view all the answers

What happens to vegetable oils when they undergo hydrogenation?

They solidify and become saturated. Signup and view all the answers

Which molecule is produced as a byproduct of the saponification of triacylglycerols?

Glycerol Signup and view all the answers

Which statement about the fatty acid composition of triacylglycerols is true?

Triacylglycerols can contain both saturated and unsaturated fatty acids. Signup and view all the answers

What determines the solubility of triacylglycerols in water?

The composition and saturation of fatty acids Signup and view all the answers

Which of the following is NOT a characteristic of triacylglycerols?

They serve as structural components of membranes. Signup and view all the answers

Study Notes

Lipids-II: Chemistry of TAGs and Phospholipids

Learning Objectives:
- Describe the properties and reactions of triacylglycerols (TAGs).
- List the main functions of glycolipids and phospholipids in the body.
- Name the main eicosanoid derivatives and their functions.

Simple Lipids

Definition: Simple lipids are composed of fatty acids and alcohol (e.g., TAGs).

Triacylglycerols (TAGs)

Structure: TAGs are composed of a glycerol backbone with three fatty acids attached via ester linkages.
Function: Storage form of lipids in adipose tissue.
Properties: Insoluble in water (hydrophobic), nonpolar, not structural components of biological membranes.
Physical properties depend on fatty acid components:
- TAGs with high proportions of unsaturated fatty acids (FAs) are liquid at 20°C (oils).
- TAGs with mainly saturated long-chain FAs are solid at ordinary temperatures (fats).
- Fats are mainly of animal origin, while oils are often from plant sources.

TAG Hydrolysis

Process: TAGs are hydrolyzed to glycerol and three fatty acids by the enzyme lipase.
Significance: This process occurs during digestion of dietary fat and breakdown of TAGs in adipose tissue.

Saponification

Process: The hydrolysis of TAGs by alkali to produce glycerol and soap.
Reaction: TAG + 3 NaOH → Glycerol + 3 R-COONa (soaps)
Importance: Creates soaps and glycerol, a triol alcohol.

Addition Reactions

Process: Addition of hydrogen or halogen to double bonds of fatty acids.
Example: Hydrogenation of oil leads to solidification and saturation.
Significance: Important in the processing of fats and oils, can modify physical properties.

Rancidity

Definition: Deterioration of fats and oils, resulting in an unpleasant taste and smell.
Cause: Occurs when fats and oils are exposed to air, moisture, light, or bacteria.
Susceptibility: Fats containing unsaturated fatty acids are more susceptible to rancidity.
Prevention: Antioxidants can prevent oxidative rancidity.

Compound/Complex Lipids

Definition: Lipids containing fatty acids, alcohol, and other molecules.
Types:
- Phospholipids: Important structural and functional components of biological membranes, amphipathic.
- Glycolipids: Widely distributed in tissues, particularly nervous tissue; occur in the outer leaflet of cell membranes, important in cell surface carbohydrates (e.g., ABO blood group substances)
- Sphingolipids: Important to cell membranes and nervous tissue, including sphingomyelins.

Phospholipids: Lecithin

Component: Fatty acid attached to the β-carbon is a PUFA molecule.
Abundance: Important and abundant component of cell membranes.
Example: Di-palmitoyllecithin (lung surfactant) is found in large amounts in the extracellular liquid layer of lung alveoli, vital for lung function.

Sphingomyelins

Structure: Composed of ceramide (sphingosine + fatty acid) + phosphorylcholine.
Function: Major structural components of nerve cell membranes (myelin sheath).
Presence: Also found in biological fluids like bile and amniotic fluid.

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Description

This quiz focuses on the chemistry of triacylglycerols (TAGs) and phospholipids, exploring their properties, functions, and reactions in the body. You'll learn about the structural components of simple lipids and the significance of eicosanoid derivatives. Test your knowledge on these essential macromolecules!