Energy Production: Lipids

Question 1

General properties of lipids?

Answer 1

Insoluble in water (hydrophobic)
contains C H O - phospholipids also contain P and N
More reduced than carbohydrates - great source of fuels as release
more energy when oxidised + needs more oxygen for complete oxidation

Question 2

What are the 3 classes of lipids?

Answer 2

• Fatty acid derivatives
• hydroxy - methyl - glutaric acid derivatives
• vitamins

Question 3

Lipids classed as fatty acid derivatives?

Answer 3

• Phospholipids (component of membranes + plasma lipoproteins)
• fatty acids (fuel molecules)
• triglycerides (fuel storage+ insulation)
• eicosanoids (lipid based signalling molecules)

Question 4

Lipids classed as HMG derivatives (C6)?

Answer 4

• Ketone bodies (C4) → water volume fuel molecules
• cholesterol (C27) → membranes + steroid hormones synthesis
• cholesterol esters → cholesterol storage
• bile acids and salts (C24) → lipid digestion

Question 5

Vitamins classed as lipids?

Answer 5

A, D, E, K

Question 6

Where are triacylglycerols stored?

Answer 6

Stored in adipose tissue

Question 7

Which hormone promotes storage of triacylglycerols ?

Answer 7

Insulin

Question 8

Storage reduced by which hormones?

Answer 8

Glucagon, adrenaline, cortisol, thyroxine, growth hormone

Question 9

How are dietary TAGs metabolised?

Answer 9

• TAGs hydrolysed by pancreatic lipase into fatty acids +glycerol (process requires bile salts and colipase)
  -Glycerol then converted to glycerol phosphate through hydrolysis of ATP to ADP
• glycerol phosphate then metabolised in liver to form dihydroxyacetone phosphate (NAD → NADH) which is used in glycolysis
• glycerol phosphate and fatty acids used in TAG synthesis if dietary in excess
• packaged into chylomicrons -released into lymphatic system as not water soluble
• stored in adipose tissue for later

Question 10

How are fatty acids catabolised?

Answer 10

• Body subjected to ‘stress’ (aerobic exercise, starvation, lactation)
• adipose tissue TAG hydrolysed by hormone-sensitive lipase (lipolysis)
• releases fatty acids and glycerol that diffuse from tissue → activated and inhibited by enzymes
• fatty acids-albumin complex (non covalently) carried to tissues → NEFA|FFA
• glycerol transported to liver- where it can be: oxidised, converted to glucose or used in triacylglycerol synthesis
• fatty acids used as source of energy (beta oxidation in mitochondria)

Question 11

Where are fatty acids activated?

Answer 11

Cytoplasm → outside mitochondria

Question 12

How are fatty acids activated?

Answer 12

• Linked to CoA using ATP - through high energy bond
• catalysed through fatty acyl CoA synthase
• activated fatty acids do not easily cross the inner mitochondrial membrane for oxidation

Question 13

Structure of coenzyme A?

Answer 13

Complex molecule, contains
vitamin pantothenic acid + -SH group, fatty acids linked to coenzyme via sulfur bond = high energy