[1.5] lipids

Question 1

what are triglycerides made up of?

Answer 1

they are made up of 3 fatty acids and a glycerol

Question 2

where are triglycerides found? (4)

Answer 2

• body fat in animals
• vegetable fat in plants
• bloodstream
  > we transport fat to and from our fat tissue at adipose tissue in the form of triglycerides
• human skin cells

Question 3

what is the structure of triglycerides?

Answer 3

• 1 × glycerol molecule
• 3 × fatty acids

Question 4

what is a saturated fatty acid?

Answer 4

a fatty acid with no double bonds present between carbon atoms

Question 5

what is a monounsaturated fatty acid?

Answer 5

a fatty acid with one C=C present

Question 6

what is a polyunsaturated fatty acid?

Answer 6

a fatty acid with more than one C=C present

Question 7

what is esterification?

Answer 7

• the formation of an ester bond between glycerol and fatty acids
• it is a condensation reaction

Question 8

how are triglycerides formed?

Answer 8

• 3 ester bonds are formed (between glycerol and fatty acid) to form a triglyceride
• 3 water molecules are released in the formation of 1 triglyceride

Question 9

how is the structure of triglycerides related to its properties?

Answer 9

1. high ratio of C-H bonds - gives it a low mass : energy ratio which means a small amount of triglycerides will release a lot of energy. this makes it an excellent energy store for both animals and plants

2. insoluble - will not affect water potential of the cell and will not dissolve and be lost from the cell so does not affect osmosis

Question 10

why are lipids important for animals living in dry conditions, such as camels?

Answer 10

when lipids are oxidised during respiration, they release large amounts of water, comparably more than proteins or carbohydrates

Question 11

what is a phospholipid?

Answer 11

a lipid with a hydrophilic phosphate group instead of one hydrophobic fatty acid tail

Question 12

what is a bilayer?

Answer 12

• phospholipids form it in aqueous environments
• a hydrophobic barrier is created between the outside and inside of the cell
• this is a basic cell membrane

Question 13

how are glycolipids formed and what is the structure of it?

Answer 13

• they are formed by combining a lipid with a carbohydrate
• a glycolipid has a glucose, a glycerol and 2 fatty acids

Question 14

what are the 6 roles of lipids in living organisms?

Answer 14

1. source of energy
2. formation of cell membrane and glycolipids
3. waterproofing - eg. waxy cuticle on leaves, sebum on mammalian skin
4. some hormones are lipid based eg. insulin
5. insulation - electrical insulation around nerve cells, heat retention in mammals
6. protection of internal organs from impact - liver, kidneys etc. can absorb shock

Question 15

what is the test for lipids (the emulsion test)

Answer 15

1. take one clean, dry test tube
2. add 2cm³ of sample
3. add 5cm³ of ethanol and shake (this dissolves lipids in sample into ethanol)
4. add 5cm³ of water and gently shake

positive result: milky white emulsion
control: water instead of sample, remains clear

Question 16

what is the role of bile?

Answer 16

• it emulsifies fats
• increases surface area for the action of lipase
• lipase breaks down lipids into fatty acids and glycerol in the small intestine