chapter 10 lipids part 1

What are lipids?

Diverse biological molecules used for energy storage, membrane structure, and signaling (messenger molecules).

Main biological functions of lipids

Energy storage, membrane structure, signaling, insulation, water repellency, enzyme cofactors, pigments, and antioxidants.

What are the two ways to classify lipids?

(1) Saponifiable vs non-saponifiable and (2) by biological function.

What are the 5 classes of lipids by function?

Energy storage, membrane, messenger, protective coating, and emulsification lipids.

Energy storage lipids

Triacylglycerols (triglycerides).

Messenger lipids examples

Steroid hormones, eicosanoids, and vitamins.

Protective coating lipids

Biological waxes.

Emulsification lipids

Bile acids and bile salts.

General structure of a fatty acid

A hydrocarbon chain with a carboxylic acid head group.

Why are fatty acids good detergents?

They are amphipathic with hydrophobic and hydrophilic regions.

Saturated fatty acid

Fatty acid containing no carbon-carbon double bonds.

Monounsaturated fatty acid

Fatty acid containing one carbon-carbon double bond.

Why are fatty acids made and broken down two carbons at a time?

They are built from acetate units that are 2 carbons.

Configuration of double bonds in natural fatty acids

Usually cis.

Fatty acid notation 18:4

18 carbons and 4 double bonds.

What is the omega (ω) carbon?

The final methyl carbon opposite the carboxyl end.

Which double bond determines omega classification?

Only the first double bond from the omega end.

Which fatty acids are essential nutrients?

Omega-3 and omega-6 fatty acids.

Why are omega-3 and omega-6 essential?

Humans cannot synthesize them.

Dietary sources of omega-3 fatty acids

Fish oil, flax seeds, and walnuts.

Role of omega-3 fatty acids in health

Important in inflammation regulation.

Effect of chain length on melting point

Longer chain length increases melting point.

Effect of chain length on solubility

Solubility decreases as chain length increases.

Effect of double bonds on melting point

More double bonds lower the melting point.

What is a kink in a fatty acid?

A bend caused by a cis double bond.

Why do kinks lower melting point?

They prevent tight packing of molecules.

Why do saturated fatty acids have higher melting points?

Straight chains pack tightly together.

What are trans fats?

Unsaturated fats made by partial hydrogenation

How are trans fats formed?

Partial hydrogenation of oils.

Why is partial hydrogenation used?

To increase shelf life.

Structure and packing of trans fats

They are straighter and pack more tightly than cis fats.

Health effect of trans fats

Increased risk of cardiovascular disease.

What is saponification?

Conversion of fats into soaps using a strong base.

General saponification reaction

Triacylglycerol + strong base → glycerol + fatty acid salts.

Products of saponification

Glycerol and fatty acid salts (soap).

Why is a metal cation present in soap?

It balances the negative charge of the carboxylate.

Examples of saponifiable lipids

Triacylglycerols, phospholipids, glycolipids, sphingolipids, and waxes.

Examples of non-saponifiable lipids

Cholesterol, bile acids, Messager lipids (steroid hormones, eicosanoids, and vitamins)

How are fats stored in the body?

As triacylglycerols.

Triacylglycerol structure

Glycerol backbone with three fatty acids attached by ester bonds.

What type of bond links fatty acids to glycerol?

Ester bonds.

Major function of triacylglycerols

Long-term energy storage.

Where are triacylglycerols stored?

In adipocytes as lipid droplets.

What enzyme breaks down triacylglycerols?

Lipases.

Why do migratory birds rely on fat storage?

Fat provides compact, efficient energy storage.

Why are fats efficient energy storage?

They contain highly reduced carbons and store more energy

Short-term vs long-term energy storage

Glucose and glycogen are short-term

triacylglycerols are long-term.

Why is energy from fats delivered slowly?

Fats must be hydrolyzed before use.

How do lipids provide insulation?

Fat deposits reduce heat loss.

Example of a lipid enzyme cofactor

Coenzyme Q.

Lipids as pigments

Carotenoids provide biological coloration.

Where do bird pigments come from?

They are obtained through the diet.

Examples of water-soluble vitamins

Vitamin C and all B vitamins.

Examples of lipid-soluble vitamins

Vitamins A, D, E, and K.

Classification of vitamins among lipids

Messenger lipids and non-saponifiable lipids.