Lecture 34: Storage and mobilisation of fuels

Question 1

Why do we need to store fuels?

Answer 1

We need fuel stores bcs the body cannot store ATP - ATP must be made in the cell at the time it is needed at the rate it is needed by oxidising fuels

• to maintain a supply of glucose between meals
• to provide immediate fuel for increases in activity
• for long period when food intake may be inadequate

Question 2

What are the main fuel reserves in the body?

Answer 2

= triacylglycerol - adipose tissue
= protein - mainly muscle
= glycogen - muscle
= circulating fuels - glucose, fatty acids etc

Question 3

How is fat stored?

Answer 3

Triacyglycerols = glycerol backgone with 3 fatty acids attached by ester bonds

• stored as fat droplets in adipose tissue
• excess fat and carbohydrate from diet can be converted to stored fat
• unlimited fat stores

Question 4

How is glucose stored as glycogen ?

Why is glucose stored as glycogen?
- what does this process require

Where does this process mainly occur ?

Answer 4

• occurs mainly in liver and muscle immediately after a meal
• requires energy inputs
• activated high-energy precursor, UDP-glucose
• glycogen synthase and branching enzyme
• stimulated by insulin

Question 5

How is glycogen mobilised?

Answer 5

• degraded by glycogenolysis
• liver glycogen = released as glucose into blood
• muscle glycogen releases fuel from glycolysis within muscle cells

Question 6

How is glucose converted to fatty acids?

Answer 6

• excess glucose carbon converted to fatty acids
• occurs mainly in the liver
• complex, energy-requiring process
• exported as TAGs in VLDL
• fatty acids stored as TAGs in adipose tissue
• stimulated by insulin

Question 7

List some examples of fuels that are used by different tissues
- brain, RBCs, liver, heart, muscle

Answer 7

Brain = glucose, CANNOT use fatty acids
RBC’s = glucose
Liver = mostly fatty acids
Heart = mostly fatty acids
Muscle = resting - mostly fatty acids 
- marathon - mix of fatty acids and glucose

Question 8

How are triacylglycerols synthesised?

Answer 8

• fatty acids from chylomicrons
• glycerol backbone from glucose
• activation of fatty acids to acyl-CoA
• esterification of acyl groups to glycerol-3-P
• stimulated by insulin

Question 9

How are triacylglycerols mobilised?

Answer 9

• hydrolysis of TAGs
• catalysed by hormone-sensitive lipase
• stimulated by hormones
  = adrenaline and glucagon
• releases of free fatty acids
• release of glycerol