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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