2.1.2j- Phospholipids and cholesterol

Question 1

List some similarities between triglycerides and phospholipids

Answer 1

• both are macromolecules and contain Carbon, Hydrogen and Oxygen
• both contain a molecule of glycerol
• both contain fatty acid chains
• in both, the components are linked together through ester bonds

Question 2

Through what reaction are ester bonds formed?

Answer 2

condensation reactions

Question 3

What is a triglyceride made up of and how are the molecules bonded?

Answer 3

a triglyceride consists of a glycerol molecule that is joined to three fatty acids by three ester bonds

Question 4

What is a phospholipid made up of and how are the molecules bonded?

Answer 4

a phospholipid is made up of a glycerol and two fatty acids, but instead of a third fatty acid a phosphoric acid molecule is bonded to the glycerol instead

Question 5

What is a phospholipid made up of (simple)?

Answer 5

a phospholipid is made up of a glycerol molecule bonded to two fatty acid chains and a phosphate group

Question 6

What part of the phospholipid is hydrophobic and which part is hydrophilic?

Answer 6

When surrounded by water, the phosphate group has a __negative________ charge and is therefore _polar_____. This means that the phosphate head is attracted to water and is referred to as being __hydrophilic_________, which means the tail is __hydrophobic________

Question 7

What is cholestrol?

Answer 7

• cholesterol is an organic molecule which is made out of carbon, hydrogen and oxygen atoms
• it is actually fairly small (and therefore not a macromolecule)
• it is not made from either glycerol or fatty acids
• but instead this steroid alcohol, a sterol, consists of four carbon-based rings known as isoprene units

Question 8

Is cholesterol hydrophilic or hydrophobic?

Answer 8

cholesterol is a hydrophobic molecule that sits in the middle of the hydrophobic part of the bilayer

Question 9

How is cholesterol used?

Answer 9

• the main part of the cholesterol molecule is embedded in membrane alongside non-polar fatty acid chains of phospholipids
• the cholesterol interacts with these chains => increases membrane packing => regulates membrane fluidity
• also acts to maintain integrity of membrane and this can be used to explain why animal cells do not need cell walls
• Cholesterol can be biosynthesised by all animal cells
• mainly made in the liver cells
• due to its hydrophobic nature, in order to transport cholesterol effectively from the liver cells to the other body cells for use in their cell membranes has to packaged within lipoproteins

Question 10

What does cholesterol make?

Answer 10

• vitamin D
• testosterone
• oestrogen

Question 11

Describe and explain how the action of a steroid hormone will differ to that of a peptide hormone at the point that it reaches its target cell (4 marks)

Answer 11

• as steroid hormones are made from cholesterol and therefore are small and hydrophobic, they can pass directly through the hydrophobic part of the cell membrane to get inside of the cell and then through any organelle membranes if necessary too.
• peptide hormones are unable to pass through the membrane and instead have to bind to receptors on the outside in order to activate another chemical on the inside of the cell, triggering a sequence of events

Question 12

Do prokaryotes have cholesterol

Answer 12

prokaryotes lack cholesterol but they have a lot of protein instead