Medical Biochemistry (2)Level 2

Part II (Lipids)week 3

Taif UniversityCollege of Medicine

Preparatory Year Students

Lipids

Lectures outlines

Definition and importance of lipids

Classification of lipids

Fatty acids structure and properties

Important reactions of FA

Glycerides

Non-glyceride lipids

Membranes Lipids

What are lipids?

Definition• A collection of organic molecules of varying chemical composition.• They are grouped together on the

basis of their solubility in nonpolar solvents.

• They are widely distributed in nature both in plants and in animals.

The great structural diversity among lipids

The defining parameter for lipids is solubility rather than structure.

What are the Biological Functions of Lipids?

Biological functions of lipidsEnergy source (Fatty acids)Energy storage (triacylglycerols)Structural components of cell membrane (phospholipids, sphingoglycolipids, and cholesterol)Hormones (steroid hormones)Emulsifiers (Bile salts)Protection and insulation (biological waxes)Source of Fat-soluble Vitamins.

What are the main Classes of Lipids?

Classification of Lipids

1. Simple lipids (Fats & Waxes) 2. Compound or conjugated lipids3. Derived Lipids4. Lipid-associating substances(Fat

soluble vitamins ,pigments,etc)

Lipids Classification

Eicosanoides

What are the general structure of fatty acids?

Fatty Acids

Fatty Acids

Usual fatty acids are unbranched Aliphatic carboxylic acids

polar Hydrophilic

Head

Nonpolar Hydrophobic Tail

Saturated Unsaturated

R

have carbon-carbon double bonds without double bonds

Fatty Acids Most naturally occurring fatty acids have a chain of an even

number of carbon atoms, from 4 to 28.

Fatty acids are usually derived from triglycerides or phospholipids.

When they are not attached to other molecules, they are known as

"free" fatty acids.

Fatty acids are important sources of fuel because they yield large

quantities of ATP.

Many cell types can use either glucose or fatty acids for this

purpose. In particular, heart and skeletal muscle prefer fatty acids.

Length of free fatty acid chains

aliphatic tails < 6 carbons Short-chain fatty acids (SCFA)

aliphatic tails 6-12 carbons Medium-chain fatty acids (MCFA)

aliphatic tails 14-22 carbons Long-chain fatty acids (LCFA)

aliphatic tails > 23 carbons Very long chain fatty acids (VLCFA)

Fatty acid chains differ by length, often categorized as short to very long.

Fatty Acids

Common fatty acids

Fatty Acids

Fatty acids

Fatty Acids

Cis Fatty Acids

Unsaturated fatty acids

Trans fatty acid

Fatty Acids

Delta () Omega ()

Numbering

-COOH-CH3 -COOH-CH3

18:2 9,12 18:2 6,9

Linoleic acid18:2

912

96

Omega-3 & Omega-6 fatty acids

Nomenclature

Stearic acidare non-systematic historical names, which are the most frequent naming system used in literature

Trivial nomenclature (or common names)

octadecanoic acidderive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry

Systematic nomenclature

(IUPAC names)

18:2 9,12 the location of the double, counting from the carboxylic acid end. Δx nomenclature

(or delta-x)

18:2 6,9 the location of the double, counting from the terminal methyl carbon

ωx nomenclature(or omega –x)

Lipid numbers take the form C:D where: C = the number of carbon atoms andD = the number of double bonds in the fatty acid

Essential fatty acids

• Fatty acids that are required by the human body but cannot be made from other substrates, and therefore must be obtained from food.

• There are two essential fatty acids: – Linoleic acid and

– Linolenic acid.

• These two acids:– (1) are needed for proper membrane structure and – (2) serve as starting materials for the production of

several nutritionally important longer-chain omega-6 and omega-3 acids

Classification Scheme for Fatty (summary) acids

PUFAMUFA

Questions• What are the differences between saturated and

unsaturated fatty acids?

• Write the chemical structure, the delta and the omega number of the following fatty acids:

Palmitic Stearic

Palmitoleic Oleic

Linoleic Linolenic