chem 134 unit 8 lipids
TRANSCRIPT
Lipids
Presented by
MICHAEL KANHAI
lipid
an oily organic compound insoluble in water but soluble in organic solvents; essential structural component of living cells (along with proteins and carbohydrates)wordnetweb.princeton.edu/perl/webwn
Classification of Lipids
Lipids
Complex lipids
Non-glyceride
lipids
GlyceridesFatty acids
Fatty Acids Long straight-chain carboxylic acids
• no branching• Most common chains range from 10–20 C in length• Usually, an even number of carbons in the chain,
including the carboxyl carbon
General formula is CH3(CH2)nCOOH, where n= even integer
Can be saturated or unsaturated, but usually no other functional groups present
Saturated Fatty Acidshave no double bondsMost common saturated fatty acids in nature are:
• Stearic acid
• Palmitic acid
Stearic acid
Unsaturated Fatty AcidsAn unsaturated fatty acid has one or more C=C
bonds in the chainC
O
OCH2CH2
C C
CH2
CH2
CH2
CH2
CH2
CH2
HH
CH2
CH2
CH2
CH2
CH3
Palmitoleic acid
– The 1st double bond is usually at the 9th carbon
– The double bond is normally in a cis configuration
– Monounsaturated one C=C– Polyunsaturated more than
one C=C bond
Oleic Acid, 18:1(9)is the most common unsaturated fatty acid in nature
Naming system for fatty acids There are four common naming systems; three of them attempt
to denote the chain length and the number and positions of any double bonds.
The first two columns show systems based on complete names,
and the last two columns show systems for denoting compounds with abbreviations.
Numbering system for fatty acids
The carboxyl-reference system indicates• the number of carbons,
• the number of double bonds,
• the positions of the double bonds, counting from the carboxyl carbon (which is numbered 1, as in the IUPAC system).
• E.g. oleic acid is: cis 18:1 9
fatty acid has 18 C atoms ( including the carboxylate C i.e. COOH)
1 double bond at C-9 Orientation around double bond is cis
The omega-reference system
• indicates the number of carbons,
• the number of double bonds
• and the position of the double bond closest to the omega carbon, (the CH3 end)
Numbering system for fatty acids
•This system is useful in physiological considerations because of the important physiological differences between omega - 3 and omega - 6 fatty acids, and the impossibility of interchanging them in the human body.
Fatty Acid PropertiesMelting point increases with increasing carbon number
Melting point of a saturated fatty acid is higher than an unsaturated fatty acid with the same number of carbons• they always form straight, rigid chains• they have no kinks and are able to pack tightly• solid at room temperature
Double bonds lower melting point relative to saturated acid• cis double bonds give them a kink along their chain length• prevent good alignment of molecules in unsaturated fatty acids
leading to poor packing• Have lower melting temperatures• Liquid at room temperature
Essential Fatty Acids
Body can make most fatty acids from carbohydrate, protein and other fats• Any fatty acid that cannot be synthesized by the body
is called an essential fatty acid • Must be obtained from the diet
Exceptions: linoleic acid and linolenic acid• Polyunsaturated fatty acids that must be obtained
from diet• Cannot be made from other materials• Cells cannot convert one into the other
Essential Fatty Acids
Sources of linoleic acid:• Leafy vegetables, nuts. Vegetable oils (seasame, corn oil,
sunflower, soybean), poultry fat
Sources o f linolenic acid:• Nuts and seeds (soybean, walnuts, flaxseed), oils (soybean,
canola)
Both play an important role in the health of the heart• Reduce plasma triglycerides
• Reduce blood clotting
• Reduce inflammatory responses in the body
Essential Fatty Acidslinoleic acid and linolenic acid are important for
synthesizing arachidonic acid (20 C atoms)
arachidonic acid in turn is the precursor for the synthesis of eicosanoids• Prostaglandins
• Leukotrienes
• Thromboxanes
COO-
arachadonic acid
Biological Processes Regulated by Eicosanoids
Prostaglandins• Mediate aspects of inflammatory response e.g. pain
and fever
• Stimulation of smooth muscle during labour (PGE2)
• Inhibit gastric secretion
• Increase secretion of protective mucus in GI tract
• Inhibition of hormone-sensitive lipases in GI tract
• Dilate renal blood vessels Results in increased water and electrolyte excretion
Biological Processes Regulated by Eicosanoids
Leukotrienes• promote the constriction of bronchi
Thromboxane • stimulates constriction of blood vessels and platelet
aggregation
Triglycerides A triglyceride (TG) places fatty acid chains at each alcohol
group of the glycerol Principal function is storage of energy Excess energy-rich nutrients stored as TG in adipose tissue When energy needed TGs broken down energy released
Fatty acid chains
Glycerolpart
Phosphoglycerides Phospholipid is a more general term
• Any lipid containing phosphate group
Phosphoglycerides contain: • Glycerol
• Fatty acid
• Phosphoric acid with an amino alcohol
Replace an fatty acid on C-3 of a TG with phosphoric acid
Because the phosphate group can ionize in solution charged lipid
Glycerol
Fatty Acid
Fatty Acid
Phosphoric Acid
Alcohol
PO42- (phosphate
group)
Phosphoglycerides
Have hydrophobic and hydrophilic domains• Polar “heads” and non-polar “tails”
Structural components of membranes
Emulsifying agents
Suspended in water, they spontaneously rearrange into ordered structures• Hydrophobic group to center
• Hydrophilic group to water
• Basis of membrane structure
Basic composition of a phospholipid. X can be a number of different substituents
Types of Phosphoglycerides
The phospho-amino-alcohol is highly hydrophilic
They are used in:• Cell membranes • Emulsifying • Micelle-forming agents in the
blood
Two types• Ones made with choline are
called lecithin• Those made with either
ethanolamine or serine are called cephalins
Phosphoglycerides are amphipathic have both polar and non-polar regions
Representation of a phospholipid
Nonglyceride LipidsSphingolipids Are not glycerides no glycerol in them
However they are similar to phospholipids
These lipids are based on sphingosine:• Long-chain• Nitrogen-containing• Alcohol
They can be modified by adding different “polar head” groups and non-polar fatty acid “tails”(via amide bond to N atom)
Fatty acids attach here
“polar head” groups attach
here
Sphingolipids
Amphipathic, like phospholipids• Polar head group• Two non-polar fatty acid tail
Structural component of cellular membranes Major categories
• Sphingomyelins Structural lipid of nerve cell membranes Myelin sheath feature
• Glycosphingolipids Also important components of muscle & nerve membranes
Nonglyceride Lipids - SteroidsContain the steroid nucleus
• A collection of 4 fused carbon rings
• Many steroids have methyl groups attached to C-10 and C-13 as well as alkyl, alcohol or ketone groups attached to C-17
SteroidsCholesterol is a common steroid
CH CH2 CH2CH2CH(CH3)2
OH
H
CH3 H
CH3
H H
H
CH3
Cholesterol
It is an amphipathic molecule (like phospholidpids)• -OH group polar
• Fused rings non-polar
Importance of cholesterol in the body
1. Cell membrane component• Its fused ring portion is readily soluble in the
hydrophobic region of membrane
• Polar -OH group sticks out of membrane
2. Precursor to bile salts• bile salts made in liver but stored in gall bladder
• Are emulsifying agents that aid in lipid digestion
3. Vitamin D synthesis
Importance of cholesterol in the body
4. Male and female sex hormones
• Through a series of reactions cholesterol can be converted to progesterone
During pregnancy progesterone suppresses further ovulation
Maintains lining of uterus to accept fertilized egg
• Progesterone can be chemically modified to give testosterone and estradiol
Involved in development of secondary sexual characteristics
O
CH3
CH3
C
CH3
O
progesterone
O
CH3
CH3
OH
testosterone
Importance of cholesterol in the body
5. Adrenal hormones• E.g. cortisol (& derivative cortisone)
enhances carbohydrate metabolism by increasing glucose and glycogen in the body
• E.g. aldosterone secreted form adrenal cortex when sodium ion levels are low in blood
• Aldosterone cause the kidneys to maximally reabsorb water and sodium ions and return to them blood.
• When sodium levels high aldosterone not secreted and so sodium ions are filtered by kidney and lost in urine
WaxesEsters of long-chain alcohols with
long-chain fatty acidsHas a weakly polar head group
(ester linkage) and non-polar tails (hydrocarbon chain)• Insoluble in water• Therefore confers water-repellant to
skin, bird feathers, leaves
Fatty acids found in waxes are usually saturated e.g. stearic acid
Alcohols may be saturated or unsaturated and may include sterols e.g. cholesterol
WaxesLinolin (woolwax) -obtained from the wool
of sheep during the cleaning or refining process • Base for pharmaceutical & cosmetic products
because it is rapidly assimilated by human skin
Spermaceti or sperm whale oil• was once in great demand as a lubricant but now is
prescribed.
• Many marine animals from invertebrates to whales contain appreciable amounts of waxes Have a variety of functions in fish, from serving as an
energy source to insulation, buoyancy and even echo location.
Biological Functions of Lipids
As an energy source, lipids provide 9 kcal of energy/gram
Triglycerides provide energy storage in adipocytes
Phosphoglycerides, sphingolipids, and steroids are structural components of cell membranes
Steroid hormones are critical intercellular messengers• See functions of cholesterol
Emulsifiers
Uses of fats in the body
Provide padding• Adipose tissue pads our body and
protects organs e.g. liver & kidney
Provide insulation• Fat under skin insulates our body
to help us retain heat
Enable the transport of fat-soluble vitamins (A,D, E, into cells of small intestine
References
wordnetweb.princeton.edu/perl/webwnwww.chemguide.co.ukhttp://www.mcgraw-hill.com/http://www.chemcases.com/olestra/olestra05.htm
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