biology form 4 lipids
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4.4 LIPIDSChapter 4 : Chemical Composition of the Cell
Lipidso Diverse group of substances that contain
o Carbono Hydrogeno Oxygeno Just as do carbohydrates BUT! in lipids the proportion of oxygen is lower than
Carbohydrates.
Example : formula for stearic acid is C₁₈H₃₆O₂
Either wise , some lipids contain nitrogen & phosphorus too .
Non-polar molecules – in soluble in waterbut
dissolve readily in other lipids & in non-polar solvents
Medium sized molecules compared to the macromolecules of polysaccharides , proteins and nucleic acid.
The main type of
Fats and oils (triglyceride
s)waxes
Phospholipids
Steroids
Importance of lipids
Store large amounts of energy for long terms
Act as source of energy
Form a major part of the structure of
the cell membranes.
Act as metabolic source of
water
Reduce the loss of water
by evaporation.
Fats and Oilso At room temperature :
o FATS are solido Oils are liquid
o Fats + oils = triglycerideso An ester that is formed through the condensation of one
molecule of glycerol and three molecules of fatty acids.o The bonds formed are called ester bond.o 3 molecules of water are removed in this reaction .o It can also be broken down into fatty acids and glycerol by
hydrolysis reactions.
Hydrolysis of triglycerides
Each molecule of fatty acids consists of a long hydrocarbon chain with a different number of carbon atoms.
Fats often contain only saturated fatty acids Oils usually contain unsaturated fatty acids.
Importance
of fats and oils
Fats and oils function efficiently as energy reserves and storage
materials.
They provide
38kJ per
gram !
but carbohydrates provide only 17kJ
per gram
Fats act as
insulator
against the loss of heat
Fatty acids
o Saturated fats - containing saturated fatty acids, solid at room temperature
o Unsaturated fats - containing unsaturated fatty acids, usually liquid in room temperature are called oils
The differences between saturated acids & unsaturated fatsSATURATED FATS UNSATURATED FATS
Examples of food that contains a high proportion of saturated fats : animal fats (lard), red meat, coconut oil, palm kernel oil, full cream milk and butter.
Examples of food that contain a high proportion of unsaturated fats : vegetables oils such as corn oil, olive oil and soybean oil.
The fatty acids in saturated fats do not have any double bond between the carbon atoms.
The fatty acids in unsaturated fats have at least one double bond between the carbon atoms. This means the carbon atoms in the hydrocarbon chain are not bonded to the maximum number of hydrogen atoms.
Cannot form any chemical bonds with other atoms or react with additional hydrogen atoms. This is because all the bonds between the carbon atoms have the maximum number of hydrogen atoms
Able to react with additional hydrogen atoms. (unsaturated fats with one double bond are called monounsaturated fats. Those with two or more double bonds are called polyunsaturated fats.)
Solids at room temperature Liquids at room temperature
Raises the level of LDL (bad cholesterol) in the blood
Increases the ratio of HDL (good cholesterol) to LDL and lowers the levels of total cholesterol an LDL in the blood
CHEMICAL BONDS
Saturated fats Unsaturated fats
Waxeso Similar to triglycerides o Long-chained moleculeso Produced by both animals and plants ; hard solids at room
temperatureo Cause the waxes to be waterproofo Found in the cuticles of the epidermis of leaves, fruits and
seeds of some plants.o Sebum that is excreted from the oil glands in the skin
contains wax that softens the skin.o Importance of waxes :
o Used to waterproof the external surfaces of plants and animalso The cuticles of a leaf and the protective covering on an insect’s body are
waxes tooo Also a constituent of honeycomb in the skin contains wax that softens the
skin.
the cuticle of a leaf is waxes.
Phospholipidso Have structure similar to triglycerides o but one of the three fatty acid molecules is replaced by a
phosphate group. o The end of the phospholipids molecules containing the
phosphate group – hydrophilic [love water].o The other end, containing the hydrocarbon chains of the fatty
acids – hydrophobic [hate water].o Importance of phospholipids :
o Phospholipids bilayers ( double layers ) form the basic of all cell membranes.
hydrophilic head
( contains phosphates group )
o two hydrophobic
o fatty acid tails
Steroids
Have a complex ring structure Synthesized in liver They occur in plants and animals. Example : cholesterol, testosterone , oestrogen and
progesterone.
Steroids Function
Cholesterol Synthesis of bile salts, steroid hormones and cell membrane
Testosterone Male reproductive hormones
Oestrogen, progesterone Female reproductive hormone
Summary of chemical compound in the cell
Aspect \ organic
compound
Nucleic acid
Carbohydrates
Proteins Lipids
Elements C, H, O, N, P
C, H, O C,H , O, N, and some have s and P
C, H, O
Monomer Nucleotides
Monosaccharide
Amino acids Fatty acids & glycerol
Types DNARNA
MonosaccharideDisaccharidepolysaccharide
Essential amino acidsNon-essential amino acids
•Fats and oils•Waxes•Phospholipids•Steroids
Importance •Store and transmit hereditary information
•Storage and supply of energy• ( 17kJ/g)
•Forming cells , enzymes, antibodies and hormones•Storage of energy •(22kJ/g)
•Storage of energy•38kJ/g•Metabolic source of water
THE END~!
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