Lipids IB Biology Topic 3

Starter!

What are lipids? Lipids are complex molecules composed of carbon, hydrogen, and oxygen. Most lipids are non-polar and are hydrophobic because they contain hydrocarbon chains. If there are double or triple bonds in the hydrocarbon chain the lipids are said to be “unsaturated”

Lipid Functions Energy storage: Fats and oils. Waterproofing: Waxes and oils Insulation: Fat layers (blubber) Cushioning: Fat layers (soles of your feet) Regulating metabolic processes: Steroids Building component of cell membranes: Phospholipids

Lipid structure (Triglyceride) A triglyceride is composed of an alcohol called glycerol covalently bonded to three fatty acid molecules by condensation reactions. This process forms three ester groups between the alcohol and one with each fatty acid chain. Is this a saturated or unsaturated Fat? Why or Why not? It is saturated because there are no double bonds between carbon atoms in the fatty acid hydrocarbon chains.

Saturated vs. Unsaturated Fats When double bonds form in hydrocarbon chains it causes them to bend. In unsaturated fats this prevents the molecules from being able to “stack” or “pack” themselves tightly, thus they remain in a liquid state at room temperature such as oils. If the hydrocarbon chains are saturated, the chains are straight and pack themselves close together forming a solid at room temperature (animal fat, butter, tallow, lard).

Steroids Steroids are cyclic hydrocarbons usually composed of four rings. They are involved with regulating metabolic processes in the body because many forms of them are hormones. Testosterone, oestrogen, and progesterone are all examples of steroid hormones. Cholesterol is the most common steroid! It is the building block for other steroid hormones and also functions in cell membrane structure. Cholesterol

Phospholipids Phospholipids are a special class of lipids composed of a phosphate group, glycerol molecule, and two fatty acid chains. The phosphate region of the molecule is polar because it is negatively charged. This makes it attracted to water or hydrophilic because of waters bipolar nature. The fatty acid chain region is composed of hydrocarbon chains which are very non-polar, therefore this end is hydrophobic or repels water.

Phospholipid Structure