Phospholipid membranes

Structure of a phospholipid

Made up of a phosphate group, glycerol unit and two fatty acid tails

Why do phospholipids form a membrane (bilayer)?

• Negatively charged (polar) phosphate head is hydrophilic

• The fatty acid tails are non-polar, they are hydrophobic

• If phospholipids are completely surrounded by water they form a phospholipid bilayer

What is meant by the term fluid mosaic model?

• proteins can move freely through the lipid bilayer 

• ease of movement is dependent on the number of unsaturated fatty acids in the bilayer 

• contain various proteins

How do fat soluble molecules and polar molecules move through a bilayer?

Fat soluble organic molecules:

• diffuse through the bilayer 

Polar molecules:

• require proteins 

Two types of proteins in bilayer

1. intrinsic proteins

2. extrinsic proteins

What are intrinsic proteins?

• completely span phospholipid bilayer 

• main transport system 

• can form channels, carrier proteins or active pumps

What are extrinsic proteins + their purpose?

• on surface of bilayer or partially embedded in it

• provide mechanical support

• act as cell receptors

What are the two types of intrinsic proteins?

1. Channel proteins

2. Carrier proteins

What are channel proteins?

Pores in the membrane that let ions diffuse through 

What are carrier proteins?

Proteins which change shape to let specific molecules through

What are glycoproteins + their function?

Protein with a carbohydrate molecule attached

• can allows cells to attach to each other (cell adhesion)

• acts as receptors for hormones and neurotransmitters

What are glycolipids + their function?

Carbohydrates attached to phospholipid molecules

• act as cell markers or antigens

Purpose of cholesterol in cell membranes 

Stabilises the membrane and regulates its fluidity