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4. Structure and Function of Cell Components:

All references are to the unit 1 Scholar book. Page numbers may vary each year as different versions of the book are released.

Lipids are important as: • long term energy source • hormones • component of membranes •insulation They are insoluble compounds found in both plant and animal cells.

Triacylglycerols (Triglycerides) •Composed of glycerol and 3 fatty acids. • Figure 4.9 p.72 •Fatty acids join to glycerol by esterification (joining of alcohol (glycerol) and acids (fatty acids)). •The OH group of glycerol reacts with COOH group of acids. •

• this is a condensation reaction since a small molecule (water) is formed when making a new product (also dehydration synthesis). • reaction is reversible, i.e., add water the compound splits (hydrolisation).

•Saturated fatty acids have only C-C single bonds. •Unsaturated fatty acids also have C=C double bonds. •Polyunsaturated – multiple C=C bonds. •Figure 4.8 p.71 •Oils (liquids) are unsaturated and come from plants and fish. •Fats (solids) are saturated and come animals.

• triglycerides are the most common lipid • mainly act as an energy store • they have more energy than same mass of carbohydrate • it is stored in adipose cells under the skin acting as an insulator

Steroids • all have the same basic 4 ring structure • side chains allow variety of roles • e.g., animal and human hormones, and membrane constituents. Steroids such as testosterone are made from cholesterol, which controls membrane fluidity. Figure 4.12 p.74

Phospholipids (Figure 4.10 + 4.11 p.72 + 73) •Formed from glycerol, 2 fatty acids, and a phosphate group. •Side chains can attach to phosphate group, giving a variety of roles. •Hydrophilic head attracted to water •Hydrophobic tail repels water => Difference in polarity – tendency to form bilayer Phosphatidylcholine (above) is most common, and is an important component of membranes.