Lecture 4.ppt
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NURS 1012: Basic Biochemistry
Lecture #4: Lipid Structure and Function
Lipids Lipids are related to fatty acids They include fats, oils and waxes Fatty acids have the general formula R-COOH
where R = H or a hydrocarbon The R group is therefore non polar and is hydrophobic
Fatty acids The hydrocarbon chain of fatty acids sometimes contain double bond(s)
and are called unsaturated fatty acids If the hydrocarbon chain contains no double bonds then the fatty acid
is saturated
Saturated Fatty Acids
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/3fatty.gif
Unsaturated Fatty Acids
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/3fatty.gif
Properties of fatty acidsSaturated fatty acids Unsaturated fatty acids
Solids at room temperature
Liquid at room temperature
They are found in animals
They are found in plants
Fatty acids Unsaturated fatty acids from plants can have their double bonds
removed by adding hydrogen. This is called hydrogenation and forms margarine a plant fat solid at
room temperature
Functions of Lipids Lipids are a storage form of energy They are insoluble and can act as food storage They are involved in membrane structure involvement They have high insulating capacity They play a role in the absorption and transport of fatty acids
(phospholipids) They play a role in hormone synthesis (cholesterol) They are carriers of fat soluble vitamins (Vit. A, D, E)
Classification of Lipids Lipids can be classified as (a) Simple
lipids/homolipids e.g. triglycerides (fats), oils and
waxes(b) Compound lipids/
heterolipids e.g. phospholipids and
glycolipids(c) Derived Lipids -
they are derived from simple and compound
lipids e.g. steroids
Simple Lipids: Triglycerides/Fats Triglycerides are the commonest lipids in nature They are non polar and are therefore insoluble in water They are less dense than water and as a result are able to float They are formed via esterification i.e. a reaction between an alcohol
(glycerol) and a tricarboxylic acid. Therefore they can undergo hydrolysis to form free glycerol and fatty acids
Diagram showing the condensation reaction between glycerol and a fatty acid (tricarboxylic acid)
Structure of triglyceride
Function of Triglycerides/Fats Triglycerides store long term energy They provide more energy per gram than proteins or carbohydrates
(4.9 kcal/gram) They act as insulators for the body They act as shock absorbers for organs
Compound Lipids: Phospholipids Phospholipids are the most abundant membrane lipids They are the structural components of the membrane They differ from triglycerides having one polar head and two
hydrophobic tails There are two types of phospholipids(a) phosphoglycerides (b) sphingomyelin
most common
The bipolar nature of phospholipids allows for the formation of
bimolecular sheets (bilayers)
Diagram of the phospholipid bilayer
http://www.bioteach.ubc.ca/Bio-industry/Inex/graphics/lipidbilayer.gif
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/ch12_lipid-bilayer.jpg
Compound Lipids: Glycolipids Glycolipids are compounds comprised of lipids linked to
carbohydrates. The carbohydrate portion forms a polar head Glycolipids are an important constituent of cell membranes,
particularly in the myelin sheath and outer surface of the nerve cells and the chloroplast membrane Both phospholipids and glycolipids form self-sealing lipid bilayers that
are the basis of all cellular membranes
http://www.ucl.ac.uk/~sjjgsca/CellMembraneComplex.gif
Derived Lipids: Cholesterol Cholesterol is in the blood of all animals Blood plasma levels range from 15 250mg/100mls Cholesterol is acquired by the body in two ways -:(a) (b)
They are produced by the cells of the body They are found in dietary sources e.g. meat and dairy products
Sites of production for cholesterol include the liver, gonads,
adrenal glands, nervous tissues and intestines
Structure of Cholesterol
Derived Lipids: Cholesterol Cholesterol is absent from plant cells, as a result vegetable oil is
considered as cholesterol free It is an important component of the cell membrane It is an important precursor of many biological compounds e.g. bile
acids and steroid hormones The end products of cholesterol metabolism are steroids (bile salts) Bile salts are formed in the liver and secreted into the small intestines
to absorb lipids When the bile salts are attached to the lipid the complex is called a
chylomicron
Derived Lipids: Cholesterol Bile salts are largely reabsorbed during lipid absorption Many steroid hormones are formed from cholesterol. These include :(a)
Aldosterone
(b) Progesterone (c) Cortisol (d) Testosterone (e) Estradiol
Derived Lipids: Cholesterol Cholesterol is insoluble in blood It travels in the blood bound to lipoproteins There are two types of lipoprotein(a) low
density lipoprotein (LDL)
(b) high density lipoprotein (HDL)
LDL is often referred to as bad cholesterol and HDL is often referred to
as good cholesterol HDLs carry LDLs away from the walls of the artery LDL sticks to the artery walls and can lead to plaque build up
(atherosclerosis)
Derived Lipids: Cholesterol Higher proportion of LDL compared to HDL is associated with
cardiovascular diseases such as heart attack and stroke
Diagram showing plaque formation in the arteries
http://www.abc.net.au/health/library/img/cholesterol_arteries.jpg
Derived Lipids: Cholesterol Diet and exercise help to maintain balance in the LDL and HDL
concentrations There exist two important cholesterol diseases(a) Familial hypercholesterolemia
This is an over production of
cholesterol(b) Zanthomatosis
This is a build up of cholesterol in the skin