Lipids

Question 1

What are the 3 compartments of the body in which lipids are mainly found?

Answer 1

1. Plasma: the colourless fluid part of blood or milk in which fat globules are suspended
2. Biological membrane
3. Adipose tissue

Question 2

What are the groups of lipids?

What are their functions?

Answer 2

1. Fatty acids: simplest form of lipids found primarily in plasma
2. Triacylglycerolds: storage form of lipids found in adipose tissue
3. Phospholipids: major lipid in biological membranes
4. Steroids: precursor molecule to bile acids, steroid hormones, and vitamin D3

Question 3

Describe the structure of the different forms of lipids

Answer 3

1. Fatty acids: non-polar repeats of CH2 + a polar COOH carboxylic acid group
2. Triacylglycerols: glycerol C3H8O3 + 3 fatty acids
3. Phospholipids: a polar hydrophilic head + non-polar fatty acid tails
4. Steroids: complex ring structure, not very soluble e.g. cholesterol

Question 4

What does amphipathic mean?

Which lipid group is amphipathic?

Answer 4

Amphipathic: a molecule having both hydrophilic and hydrophobic parts

Fatty acids are amphipathic:

• The hydrocarbon chain (CH2)n non-polar repeats is the hydrophobic part and renders fatty acids insoluble in water
• The carboxylic acid group (-COOH) is the hydrophilic part

Question 5

What are the different types of fatty acids?

Answer 5

1. Saturated: all the links between the adjacent carbons in the hydrocarbon chain are single bonds
2. Unsaturated: one or more pairs of carbons are linked by a double bond
   
   1. Monounsaturated
   2. Polyunsaturated

Question 6

What is the reaction to produce a triacylglycerol called?

What is the function of triacylglycerols and how is this effected?

Answer 6

Esterification

Glycerol + 3 Fatty acids = TAG

Triacylglycerols are the storage form of lipids (found mainly in adipose tissue)

The release of their energy is effected by hormonal signals, whereby the TAG is broken down to its constituent glycerol and 3 fatty acids, which are released back into the plasma (from adipose tissue) for energy production

Question 7

List the constituent molecules of a phospholipid

Answer 7

Hydrophilic head:

1. Glycerol
2. Phosphate group
3. R group (on top of phosphate group): polar

Hydrophobic tail

1. 2 Fatty acids

Question 8

What happens to phospholipids in aqueous solution?

Answer 8

Spontaneously form lamellar structures, bilayers, and liposomes

Question 9

What kind of a lipid is cholesterol?

What is its function?

Answer 9

Cholesterol is a steroid

1. It is essential for cellular structure: influences cell membrane fluidity (NOT covalently bonded to cell membrance, can therefore move readily)
2. It is a precursor molecule for bile acids, ALL steroid hormones and Vitamin D3 which is important in calcium metabolism.