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203 Lipids

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LIPIDS
http://www.rediscoverdairy.co.za/
What are Lipids?
• Lipids are loosely defined group of
molecules with one main characteristic:
they are insoluble in water
• Their chemistry is highly varied
• They all dissolve in organic solvent e.g.
Ether, chloroform and benzene
• Made up of carbon, hydrogen and oxygen
but have lower proportion of oxygen than
carbohydrates
Functions
• Lipids store energy
-Contains more energy than carbohydrates
• Lipids make membranes
• Lipids serve as insulator
• Some lipids serve as chemical messengers
• Others communicate signals
Classes of Lipids
• Fats and oils
• Phospholipids
• Waxes
• Steroids (like cholesterol)
Fats and Oils
• They are the commonest lipids in nature
• Fats and oils are chemically extremely
similar but at room temperature fats are
solids (saturated) while oils are liquids
(mostly unsaturated)
• Animals store fat (energy and insulator)
• Plants store oils rather than fats (seeds/nuts)
• Building blocks- fatty acids and glycerol (an
alcohol)
Fatty acid structure
http://biology.clc.uc.edu/courses/bio104/lipids.htm
Fats & Oils (Saturated & Unsaturated)
http://biology.clc.uc.edu/courses/bio104/lipids.htm
3 Condensation reactions (esterification)
Lipid (Triglyceride) formation
http://weloveteaching.com/
Triglyceride
Ester link
Grouping of fatty acids
• Fatty acids with less than 6 carbons in their
chains may collectively be called shortchain fatty acids, usually called carboxylic
acids and are not “fatty” acids.
• Those with 6 to 12 carbons are mediumchain fatty acids.
• Those with 14 to 22 carbons are longchain fatty acids
• Those with over 22 carbons are the verylong-chain fatty acids.
Grouping of fats and oils
• Those which contain primarily medium-chain
fatty acids are called to medium-chain
triglycerides (MCTs).
• Those which contain primarily long-chain
fatty acids are called long-chain triglycerides
(LCTs).
• Most of the fats and oils in our diets and the
common names we know are LCTs.
Examples of fatty acid and their source
• Butyric acid (C4): Milk
• Lauric acid (C12): Nutmeg; Palm kernel
• Myristic acid (C14): Nutmeg; Palm kernel
• Palmitic acid (C16): Olive oil; Animal lipids
• Stearic acid (C18): Cocoa butter; Animal lipids
Phospholipids
• These are lipids containing a phosphate
group e.g. Lecithin in eggs
• Phospholipids are also made from
glycerol, two fatty acids, and
a phosphate group (in place of the
third fatty acid) with some other
molecule attached to its other end.
Structure of Phospholipids
Functions of Phospholipids
• Vital component of cell membranes
• Needed for the formation of
neurotransmitter substances (for nervous
system)
Phospholipids molecule
• The lipid part (hydrocarbon tails of the fatty
acids) are hydrophobic (water-hating,
hence insoluble in water), but the
phosphate group end is hydrophilic (water
loving, hence soluble in water). This means
that phospholipids are soluble in both
water and oil.
Phospholipids Bilayer
• Our cell membranes are made mostly
of phospholipids arranged in a double
layer.
• The tails from both layers are “inside”
(facing toward each other) and the
heads are facing “out” (toward the
watery environment) on both surfaces
Lipid bilayer
http://people.csail.mit.edu/seneff/lipid_bilayer.jpg
Phospholipids bilayer illustration
Water
Hydrophobic tail
(Fatty acid)
Hydrophilic Head
(Phosphoric acid)
Oil
Water
Waxes
• These are lipids made up of very long chain fatty
acids joined to alcohols.
• Difference between fats and waxes is the joining of
only one fatty acid to each alcohol in waxes
because the alcohol only have one hydroxyl group
unlike glycerol with three in fats.
• Waxes are very insoluble & are used by plants and
animals for water proofing.
• Some waxes produced by insects to protect their
cuticle from water loss can withstand extreme high
temperatures without melting.
Steroids
• Found in membranes
• Also function as hormones
• E.g. Cholesterol (found in most animal cell
membrane), testosterone, estrogen
• Composed of 4 fused carbon rings
• Various other groups/molecules are
attached around the edges
Structure of steroid
Cholesterol
• Our bodies make about 2 g of cholesterol
per day (85% of blood cholesterol).
• Only about 15% comes from dietary
sources.
• Cholesterol is the precursor to our sex
hormones and Vitamin D.
• Vitamin D is formed by the action of UV
light in sunlight on cholesterol molecules
that have “risen” to near the surface of
the skin.
Vitamin D production & metabolism
http://www.scientificpsychic.com/health/vitamins.html
Vitamins and Minerals
Vitamins
• Vitamins are used to produce energy and
synthesize tissues, enzymes, hormones, and
other vital compounds.
• Some are soluble in fat (Vit A, D, E and K) and
some soluble in water (Vit B complex-B1,2,6,12 &
C and many more)
Quick Quiz
1. In a tabular form, list the various vitamins
you know, their major functions and
sources.
• i.e. Vit/Functions/Sources
2. List some minerals required by living
things.
• Name & Matric number
• 8 minutes
Read up these at home (refresh yourself)
Minerals
• Sourced from inorganic salts or as part of carboncontaining organic compounds.
• Magnesium is present in chlorophyll, the pigment
that makes plants green.
• NPK- component of inorganic fertilizer for plant.
• Six minerals are required by people in gram
amounts (macrominerals): Na, K, Ca, Mg, P and
Cl. Daily requirements range from 0.3 to 2.0
grams per day.
• Nine trace minerals (microminerals)- Cu, I, Fe, F,
Mn, Zn , Cr (Chromium), Mo (Molybdenum), Se
(Selenium).
Functions of some minerals
• Calcium is the most abundant mineral in the
human body. More than 99% of total body
calcium is stored in the bones and teeth. Calcium
is also found in body fluids where its function is
to regulate contractions of blood vessels and
muscles.
• Iodine is primarily involved in the synthesis of
thyroid hormones.
• Iron is a component of haemoglobin, myoglobin,
and many enzymes in the body.
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