LIPIDS

Lipids are hydrophobic molecules composed of C, O, and H. In general, they contain fewer O-H bonds and more C-H bonds than carbohydrates do. If they are

hydrophobic, what will they dissolve in?

WHAT DO ORGANISMS USE LIPIDS FOR?

• Storing Energy• Building Membranes and other cell parts• Chemical Signaling Molecules

Types of Lipids (families)

• Fats• Phospholipids• Steroids• Waxes

Fats

• Most common energy storing molecule• 1 gram of fat stores 38 kJ (9 kilocalories)– (one calorie (cal) = 4.18 J, 1 Cal (1kcal) = 4.18 kJ

• What is a calorie?

Adipose Tissue

• Animals convert excess carbohydrate to fat • Fat molecules are stored in fat droplets in the

cells of adipose tissue• The layer of fat beneath the skin acts as

thermal insulation

Adipose tissue

Plants and fats

• Plants store fats as oils• Fats and oils are made from two kinds of

molecules: glycerol and fatty acids

Structure of Fatty Acids

• “tail” of a fatty acid is a long hydrocarbon chain (16 -18 carbons long), making it hydrophobic. The “head” of the molecule is a carboxyl group which is hydrophilic.

Most common lipid

• Triglycerides– Glycerol and 3 fatty acids

Saturated vs Unsaturated Fatty Acids

•Saturated fatty acids have only single bonds between carbons atoms

•They are saturated because they have the maximum number of H bonds attached to the carbons

•Unsaturated fatty acids have one or more carbon = carbon double bonds

•They have fewer than the maximum number of H bonds attached to the carbons

Poly and mono saturated

• Polyunstaturated fatty acids• Have many C=C bonds

• Monounsaturated fatty acids have one C=C bond

Solid vs liquid

• Straight chains of fatty acids allows them to fit together very closely allowing van der Waals forces along the length

• (Van der Waals forces occur between molecules of the same substance– They include dipole forces, dispersion forces and

hydrogen bonding)• Result is solid consistency at room

temperature

Solid vs Liquid

• Unsaturated fatty acids are commonly found in plant oils

• The bending of the hydrocarbon chains with C=C prevents/reduces van der Waal attractions, causing oils to be liquid at room temperature

(see page 36 in text)

Hydrogenation

• Industrial process that adds H atoms to the C=C bonds of unsaturated fatty acids – rendering vegetable oils to be solid at room temperature

Cis and Trans Fatty Acids

The Latin prefixes Cis and Trans describe the orientation of the hydrogen atoms with respect to the double bond.

•Cis means "on the same side" and •Trans means "across" or "on the other side".

•Naturally-occurring unsaturated vegetable oils have almost all cis bonds•Trans fatty acids are carcinogenic

Cis Trans

Phospholipids

• glycerol + two fatty acids + a phosphate group

Hydrophobic and Hydrophilic• The fatty acids - hydrophobic, • The phosphate group - hydrophilic • This means that phospholipids are soluble in

both water and oil.

Micelle• When added to water, phospholipids form spheres –

micelles. (see page 38)• The hydrophilic heads dissolve in water, the

hydrophobic tails mix in the centre of the sphere

Membranes and Phospholipids

•Cell membranes - double layer of phospholipids •Fatty acids form “inside”•Phosphate group face “out” on both surfaces.

Function of Cell Membrane

• Separates two “water” compartments– Cytoplasm and extracellular fluid– Allows two areas to distinct

• Homework – describe a cell membrane and the function of it.

• http://www.cytochemistry.net/Cell-biology/membrane_intro.htm

Steroids

Good Steroids

• Estrogen, progesterone, corticosteroids, aldosterone, testosterone, and Vitamin D.

• Four fused hydrocarbon rings and functional groups.

Cholesterol

•Precursor to sex hormones and Vitamin D•Sunlight changes cholesterol to Vit. D

•Is important part of cell membranes •Gives a fluid nature to membrane in colder temperatures

Artherosclerosis

• Read Page 38 of your text and describe what this is.

Waxes

• Long chain fatty acids linked to alcohols or carbon rings

• They form firm, pliable molecules• Useful as waterproof coatings for plants and

animals– Cutin covers leaves, stems and fruit– Beeswax used to construct honeycombs

Task

• Questions 11 – 18 on page 40