Structure and function of cell components (i)Carbohydrates (ii)Lipids (iii)Proteins (iv)Nucleic Acids (v)Membranes (vi)Cytoskeleton

Lipids All relatively insoluble in water Made of C, H, O (with less O in proportion to C and H compared to carbohydrates) Fats and oils are familiar lipids Fats tend to be solid at room temperature Fats tend to be solid at room temperature Oils tend to be liquid at room temperature Oils tend to be liquid at room temperature 3 lipids are of importance to cells Triglycerides (triacylglycerol) Triglycerides (triacylglycerol) Phospholipids Phospholipids Steroids Steroids

Structure of glycerol Glycerol is a three carbon alcohol that contains 3 –OH (hydroxyl) groups

Structure of Fatty Acids Fatty acids are hydrocarbon chains ending in a carboxyl group (COOH) HO – C – R O R is an abbreviation for any organic group About 30 different fatty acids are commonly found in lipids (they nearly always have an even number of carbon atoms).

Structure of Fatty Acids cont… Saturated fatty acids All available bonds are occupied by hydrogens All available bonds are occupied by hydrogens E.g E.g Palmitic acid CH 3 (CH 2 ) 14 COOH Stearic acid CH 3 (CH 2 ) 16 COOH OH – C – C – C – C – C – C – C – C – C – C – C – C – C – C – C – CH 3 O

Structure of fatty acids cont… Unsaturated fatty acids Some carbon atoms are double bonded with one another, therefore they are not fully saturated with hydrogen Some carbon atoms are double bonded with one another, therefore they are not fully saturated with hydrogen E.g. Oleic Acid CH 3 (CH 2 ) 7 CH = (CH 2 ) 7 COOH E.g. Oleic Acid CH 3 (CH 2 ) 7 CH = (CH 2 ) 7 COOH Note - this is monounsaturated (1 double bond) Note - this is monounsaturated (1 double bond)

Structure of fatty acids cont… E.g. Linoleic acid CH 3 (CH 2 CH=CH) 3 (CH 2 ) 7 COOH E.g. Linoleic acid CH 3 (CH 2 CH=CH) 3 (CH 2 ) 7 COOH Note – this is polyunsaturated (more than 1 double bond) Note – this is polyunsaturated (more than 1 double bond)

Formation of Ester Linkages Glycerol and fatty acids are joined together by dehydration (condensation) reactions The bond linking glycerol and fatty acids is called an ester bond

Formation of ester linkages cont… HO – C – R O C C C H H H H H OH

Formation of ester linkages cont… C C C H H H H H OH O – C – R O H2OH2O Ester bond

Structure of Triglycerides A triglyceride molecule is the result of a glycerol molecule forming ester linkages with 3 fatty acids The type of triglyceride formed is dependent on the fatty acids present

Structure of Phospholipids A phospholipid consists of a glycerol molecule attached to 2 fatty acids, and a phosphate group which is linked to an organic compound (e.g. choline)

Structure of phospholipids cont… The fatty acid portion of a phospholipid is not soluble in water (hydrophobic) The glycerol and organic base of a phospholipid is water soluble (hydrophilic) In water phospholipids form a bilayer with the hydrophilic head pointing outwards and hydrophobic tail inwards

Structure of Steroids Steroids consist of 4 hydrocarbon rings with slightly different side chains. The length and structure of the side chains distinguish one steroid from another.

Functions of Lipids Structural Membranes Membranes Phospholipid bilayer Cholesterol is part of animal cell membranes (plants have a similar molecule) Adipose tissue cells (contain lipid droplets) Adipose tissue cells (contain lipid droplets) Cushions vital organs Insulation Insulation Endothermic animals have layers of fat cells below the skin to prevent heat loss

Functions of lipids cont… Storage Energy storage Energy storage Triglycerides – insoluble therefore has no influence on osmosis Fat and lipid molecules are very compact Release large amounts of energy Water storage Water storage Fat in camel humps releases water (as well as energy) when respired.

Functions of lipids cont… Hormones Steroid hormones regulate metabolism in a variety of animals including vertebrates, insects and crabs Steroid hormones regulate metabolism in a variety of animals including vertebrates, insects and crabs Cholesterol reduces the fluidity of the membrane Cholesterol reduces the fluidity of the membrane Cholesterol prevents solidification at low temperatures Cholesterol prevents solidification at low temperatures

Learning Activities Read and take notes from DART pg 32 – 37 Scholar (section 4.3) Lipids worksheet Use the internet to familiarise yourself with different ways of presenting the chemical formulae / structures Posters and diagrams (compare / contrast) Advanced Higher Questions