Download PPT

Chapter 18:
Lipids
1
IMPORTANT FUNCTIONS OF LIPIDS
•
•
•
•
Protective wax coatings found on some plants
Energy-rich compounds with low densities
Storage form of energy for plants and animals
Structural components, especially in cellular membrane
formation
2
LIPID
• A biological compound that is soluble only in nonpolar
solvents.
3
FATTY ACIDS
• Building blocks of many lipids
• Long chain carboxylic acids
4
FATTY ACIDS, cont.
• In water, fatty acids will form micelles.
5
FATTY ACIDS – COMMON CHARACTERISTICS
•
•
•
•
Usually straight chains (no branching)
Sizes usually range from C10 to C20
Usually have an even number of carbons
Can be saturated (no C=C bonds) or unsaturated (has
C=C bonds, usually in the cis configuration)
• Examples of saturated, monounsaturated, and
polyunsaturated fatty acids containing 18 carbon atoms:
6
FATTY ACID – MOLECULAR SHAPES
• C=C causes “kinking” of the carbon chain
7
FATTY ACIDS – MOLECULAR SHAPES, cont.
• Fatty acids with C=C bonds cannot pack closely together
because of shape. This leads to decreased intermolecular
attractions and lower melting points.
• Fatty acid melting points decrease as the number of C=C
bonds increases.
• Most unsaturated fatty acids are liquids at room
temperature.
8
ESSENTIAL FATTY ACIDS
• Those needed by the body, but not synthesized within the
body in adequate amounts.
• For humans, linoleic and linolenic acid are essential, but
easily obtainable from plant and fish oils.
9
STRUCTURE OF FATS AND OILS
• Fats
Usually from animal sources
Solids at room temperature
Contain a high degree of saturated fatty acids
• Oils
Usually from plant and fish sources
Liquids at room temperature
Contain more unsaturated fatty acids
10
STRUCTURE, cont.
• Fats and oils are triglycerides (triglycerols) which are
triesters of glycerol.
11
STRUCTURE, cont.
• An example of the esterification process:
12
REACTIONS OF FATS AND OILS
• Hydrolysis – important for fat and oil digestion
13
REACTIONS, cont.
• Saponification – the commercial production of the salts of
fatty acids (soaps)
14
REACTIONS, cont.
• Hydrogenation – decreases the degree of unsaturation,
used to make margarines from oils
15
WAXES
• Esters of fatty acids and long chain alcohols
Water insoluble and not easily hydrolyzed
Often found in protective coatings
16
PHOSPHOGLYCERIDES
• A phospholipid that contains an alcohol
(usually an amino alcohol)
17
IMPORTANT PHOSPHOGLYCERIDES
• Lecithins
Contain the amino alcohol choline
Important cell membrane component
Emulsifying agent
• Cephalins
Contain ethanolamine or serine as the alcohol
Found in most cell membranes, especially brain tissue
18
SPHINGOLIPIDS
• Sphingolipids contain sphingosine rather than glycerol.
• Two types of sphingolipids exist:
•Sphingomyelin contains a phosphate and choline
group. It is found in the myelin sheath surrounding
nerve cells.
•Glycolipids contain carbohydrates
unit. They are often called
cerebrosides because of their
abundance in brain tissue.
19
SPHINGOLIPID STRUCTURE
20
CELL MEMBRANES
• Prokaryotic Cells – simple unicellular organisms with no
internal membrane structures
• Eukaryotic Cells – cells containing membrane-enclosed
organelles, particularly a nucleus
21
MEMBRANE STRUCTURE
• Most are 60% lipid, 40% protein
• Lipids in membranes: phosphoglycerides, sphingomyelin,
and cholesterol
• Lipids are organized in a bilayer with hydrophobic (long
carbon chain) portions inside and hydrophilic (polar
groups) exposed to the water environment.
22
FLUID MOSAIC MODEL OF MEMBRANE STRUCTURE
23
STEROIDS
A broad class of compounds that have the same structural
feature:
Like all lipids, steroids are soluble in nonpolar solvents.
24
STEROIDS, cont.
• Cholesterol – the most abundant steroid in the human
body
Essential component of cell membranes
Precursor of other important steroids
Synthesized by liver and present in foods
Strong correlation between cholesterol blood levels and
atherosclerosis
25
STEROIDS, cont.
• Bile salts – bile is produced by the liver, stored in the
gallbladder, and emptied into the intestine
Bile salts emulsify lipids in the intestine, breaking
apart lipid globules
Increased surface area allows lipids to be more easily
hydrolyzed
26
STEROID HORMONES
• Hormone – a chemical messenger secreted by specific
glands and carried through the blood to a target tissue,
where it triggers a particular response
• There are two major categories of steroid hormones:
adrenocorticoid hormones and sex hormones.
27
ADRENOCORTICOID HORMONES
Produced by the adrenal glands
Two classes:
• Mineralocorticoids – regulate the concentration of ions in
bodily fluids
Aldosterone – increases absorption of Na+ and Cl• Glucocortiocids – enhance carbohydrate metabolism
Cortisol – increases glucose and glycogen concentrations
in the body
28
SEX HORMONES
• Androgens – Male sex hormones produced by testes,
including testosterone
• Estrogen and Progesterone – female sex hormones
produced by ovaries, including estradiol and estrone (the
most important estrogens)
29
PROSTAGLANDINS
• Cyclical compounds synthesized from arachidonic acid
• Similar to hormones in that they are intimately involved
in a host of body processes
• Involved in almost every phase of reproduction
• Participate in blood clotting
30
THERAPEUTIC POTENTIAL OF PROSTAGLANDINS
• PGE2 and PGF2 induce labor and used for therapeutic
abortion in early pregnancy
• PGE2 in aerosol form used to treat asthma - opens up
bronchial tubes by relaxing the surrounding muscles
• Others inhibit gastric secretions and used to treat peptic
ulcers
• Many researchers believe that when they are fully
understood, prostaglandins will be found useful for
treating a much wider variety of ailments
31