3.1.3 lipids

What are lipids vital for? (3)

Provide buoyancy

long term store of energy protect vital organs

hydrophobic so it can act as a waterproof layer for organisms

Two types of lipids

triglycerides and phospholipids

3 triglycerides properties

High bond energy due to high proportion of C - H bonds so lipids can store lots of energy

non-polar molecule does not attract hydrogen ions so insoluble so doesn't affect water potential during osmosis

high ratio of hydrogen: oxygen atoms so lipids can release water when oxidised so good for desert animals

Describe triglyceride structure

Formed by condensation reaction between 1 glycerol molecule and three fatty acid molecules

Formation of triglycerides

A condensation reaction between glycerol and 3 fatty acids (RCOOH), with the elimination of 3 molecules of water and the formation of 3 ester bonds.

Fatty acid structure

Definitions of saturated and unsaturated fatty acids. How do we know if a fatty acid is saturated or unsaturated?

Saturated fatty acids: fatty acids which only contain single bonds between carbon atoms

Unsaturated fatty acids: fatty acids which contain at least one double bond between carbon atoms

This depends on its hydrocarbon 'R' group

Which one is saturated with hydrogen atoms:

Unsaturated fatty acids

Saturated fatty acids

Saturated fatty acids Not unsaturated fatty acids

Structure of unsaturated fatty acid chain

The fatty acid chains are rigid. The chains have bends (kinks) in them (where the double bonds occur). This means that they can’t line up closely next to each other

Structure of saturated fatty acid chains

The fatty acid chains are flexible. The chains are straight, so they

can line up closely next to each other

Which is viscous & more dense-

Unsaturated fatty acids

Saturated fatty acids

Saturated fatty acids

Which has a higher m/boiling point (therefore more intermolecular forces)?

Unsaturated fatty acids

Saturated fatty acids

Saturated fatty acids

State of matter at room temp for:

Unsaturated fatty acids

Saturated fatty acids

Unsaturated fatty acids: liquid usually

Saturated fatty acids: solid usually

Phospholipid structure

A condensation reaction between glycerol and a fatty acid forms an ESTER BOND

SO 1 glycerol is attached to...

• 2 fatty acids

• 1 phosphate group

T OR F: triglycerides and phospholipids are both fully hydrophobic

False because phospholipids have hydrophilic head and hydrophobic tail

T or f: hydrophobic tail repels water and mixes with fats

T

What holds together the hydrophobic tails?

Van der Waals forces and hydrophobic interactions hold the phospholipid tails together

What do phospholipids form in water? (3)

bilayer in water

micelles in water

monolayer on surface

Describe how phospholipids can arrange themselves to form a cell membrane

The plasma membrane is a phospholipid bilayer, with hydrophilic phosphate

heads on the outside of the bilayer and hydrophobic fatty acid tails on the inside

of the bilayer.

• The hydrophilic phosphate heads attract water to either side of the bilayer /

point towards water.

• The hydrophobic fatty acid tails repel water / point away from water.

T OR F: lipid isn't a polymer

True because it does not consist of repeating units