B: Lipids

Question 1

Functions of Lipids

Answer 1

• energy storage
• thermal insulation
• structural components of cell membranes
• protection of organs
• storage and transport for hydrophobic vitamins
• hormones
• electrical insulation (protection of neurons - Myelin)

Question 2

Energy of Fats vs Glucose

Answer 2

Fats

• Oxidation C₅₇H₁₀₀O₆ // C = -1.54 —> CO₂ C = 4
• Oxidation no. increases more –> gives more energy
• fats stored in cells and are hydrophobic –> do not affect the movement of H₂O

Glucose

• Oxidation C₆H₁₂O₆ // C = 0 —> CO₂ C = 4
• oxidation number increases less than that of fat
• water soluble –> easily transported around the body

Question 3

Triglycerides

Answer 3

• most abundant class of lipids
  
  • most fats and oils in our diet contain triglycerides
• viscous because of H bonds

glycerol + fatty acids —> triglyceride + 3H₂O

condensation reaction

Question 4

Unsaturated Fats

Answer 4

• Saturated fats: No C=C bond
• Mono-saturated: 1 C=C bond
• Polyunsaturated: many C=C bonds
• difference of 2H atoms indicates the presence of C=C bonds

C₂H₃ C₂H₅

^{unsaturated saturated}

• the arrangement of double bonds in fatty acids is almost always cis

Question 5

Melting points of Lipids

Answer 5

Mr

• Larger the Mr, the higher the melting / boiling point
  
  • more energy required for them to move faster and break free from their IMF

Length of Carbon bonded Chain

• Longer chain means greater degree of LDF –> will pack closer
• shorter chain has a smaller surface area of contact

Unsaturation

• number of C=C bonds in the carbon –> kinked chains can’t pack as closely
  
  • the more unsaturation there is, the lower the melting point

Question 6

Degree of Unsaturation - Iodine number

Answer 6

• Iodine molecules will add across a C=C

Iodine number: number of grams of iodine that will react with 100g of fat / oil

• completely saturated –> Iodine no. = 0
• High degree of unsaturation, high iodine number

Question 7

Phospholipids

Answer 7

• main lipid found in cell membranes
• a membrane is made up of a bilayer of phospholipids surrounding each cell and phospholipids also surround inner structures in the cell (organelles)

Question 8

Hydrolytic Rancidity

Answer 8

• The process whereby fats and oils in foods are hydrolysed to give fatty acids and glycerol
• process speeded up by
  
  • enzymes
  • high temps
  • excess moisture
  • high/low pHs

Question 9

Oxidative Rancidity

Answer 9

• When presence of O₂ breaks down the fats and oils in food
• Occurs in unsaturated fats / oils where C=C bonds react with O₂ in a free radical reaction —> aldehydes and ketones
• Process speeded up by
  
  • high con. of oxygen
  • UV light
  • high temps
  • presence of metals

Question 10

Hormones - Steroids

Answer 10

• chemical messengers
• all share the same steroidal backbone
• Uses - treatment for
  
  • Asthma
  • diabetes
  • contraception
  • skin conditions
  • bone/ blood disorders
  • muscle growth

Question 11

Lipoproteins

Answer 11

Cholesterol is largely hydrophobic –> solubility in blood plasma is low –> normally transported throughout the body in Liporotein complexes

Question 12

Low Density Lipoproteins

Answer 12

Bad cholesterol

• less soluble in blood plasma and are more likely to deposit as a solid (plaque) in artery walls –>
• blood clots –>
• oxygen and glucose can’t get to heart muscle cells
• can no longer respire –>
• cells don’t receive energy and die –> heart attack

Question 13

High Density Lipoproteins

Answer 13

Good cholesterol

Question 14

Lipoproteins Density and Solubility

Answer 14

• density - long chains and kinks increases, density decreases
• solubility - more lipids, more hydrophobic environment, solubility decreases
• density and solubility of lipoproteins decreases with increasing lipid content

Question 15

Acid Hydrolysis of Fats

Answer 15

—–> glycerol + fatty acids

Question 16

Alkaline Hydrolysis of Fats

Answer 16

—> glycerol + anion fatty acids

Question 17

Phospholipids Hydrolysis of Fats

Answer 17

—-> Glycerol + Phosphoric acid + 2 Fatty acids +