Medical Biochemistry (2) Level 2 Part II (Lipids) week 3 Taif University College of Medicine Preparatory Year Students
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