2.2.7 (Lipids 3 - Phospholipids and cholesterol)

What is the structure of a phospholipid?

• 2 fatty acid molecules, A glycerol molecule and a phosphate molecule

How is the phosphate bonded to the glycerol?

• It is bonded using condensation reaction between phosphoric acid and 1 of the 3 -OH molecule to form an ester bond

What are the 2 parts make up a phospholipid?

• The hydrophilic phosphate head

• The hydrophobic fatty acid tails

Explain why the head of a phospholipid is described as hydrophilic

• It is attracted to water molecules

• because head is polar

Why is the phosphate head of a phospholipid polar ?

• Because the phosphate head is negatively charged

Why is the Fatty acid tail hydrophobic

• Because it is non-polar which means that it repels polar molecules, mainly water

Explain why phospholipids are described as amphipathic

Because it has a hydrophobic, non-polar, region (tail) and a hydrophilic, polar, region (head)

what does amphipathic mean?

• When a molecule have both a hydrophilic and hydrophobic part

What are the 3 ways in which phospholipids behaves in water

• They may form a layer on the top of the water where the tails are sticking out of the water and the heads are submerged in the water

• They may also form micelles - Tiny balls with the tails being tucked inside and the heads pointing outwards

• They may also form - A small ball with a bilayer where there are 2 layers of phospholipids pointing towards each other and the heads sticking out in both directions

Where is the phospholipid bilayer found?

• Around the cells and cell organelles

How is the phospholipid bilayer formed?

• They form in aqueous conditions

• The tails point towards each other due to them being hydrophobic and not wanting to be in contact with water

• The heads point outwards due to them being hydrophilic and being able to bind to water

What makes the phospholipid selectively permeable?

• it only allows small, non-polar and fat-soluble molecules through the phospholipid bilayer such as O2 and CO2

What is cholesterol?

• It is a steroid alcohol which is a type of lipid which is not made of glycerol and fatty acids

What does cholesterol consist of?

• It consists of 4 carbon-based rings

Is cholesterol hydrophobic or hydrophilic and what does it mean?

• It is a hydrophobic molecule

• It means that it can sit in between phospholipids in the phospholipid bilayer

Where is cholesterol produced?

• Produced in the liver mainly

What is cholesterol plants called and what is the difference between human cholesterol and plant cholesterol?

• stigmasterol

• The difference is that there is a C=C between the C22 and the C23

What are examples of steroid hormones and what are they produced by?

• Testosterone

• Oestrogen

• Vitamin-D

• They are made from cholesterol