lecture 35 - fuel storage & metabolism Flashcards
Is ATP an energy store?
No - energy is stored in glycogen and fat
Is ATP transferred between tissues or made in the tissue that needs it?
made in the tissue that needs it
In what form is fat stored in tissues?
TAG as fat droplets in adipose tissue
What form are fatty acids derived from for TAG synthesis and fuel storage?
fatty acids from chylomicrons and VLDL metabolism
Where are the glycerol backbones (glycerol-3-phosphate) sourced from in synthesis and storage of TAGs?
From glucose
What is the process of TAG storage mediated by?
The hormone insulin
What reaction forms TAGs from glycerol-3-phosphate and free fatty acids?
Esterification, with the fatty acids first converted to fatty acyl-CoA
What enzyme is activated by adrenaline and glucagon when TAG stores need to be mobilised?
Hormone-sensitive lipase
What hormones activated hormones-sensitive lipase, and in what situations?
Adrenaline (exercise), glucagon (in fasting)
What is the function of hormone sensitive lipase?
Acts to hydrolyse TAG molecules to release fatty acids and glycerol when stored energy is required.
What is glycerol used by?
The liver
What type of bond are glucose units joined by in glycogen?
alpha (1-4) glycosidic bonds with branches introduced by alpha(1-6) glycosidic bonds
Where is glycogen stored?
As granules in the cytoplasm of liver and muscle cells, which also contain the enzymes required for their synthesis and degradation.
What supplies the energy for glycogen synthesis?
ATP and UTP
What is the role of ATP in glycogen synthesis?
Supplies energy for the phosphorylation of glucose to glucose-6-phosphate
What is the role of UTP in glycogen synthesis?
Makes the activated high-energy precursor of glycogen, UDP-glucose
What is the process of glycogen breakdown?
Glycogenolysis
What hormones stimulate glycogenolysis?
Adrenaline and glucagon
In what circumstances is stored glycogen released from the liver?
Gradually degraded between meals to maintain a steady concentration of glucose in the blood to fuel the brain and other glucose-dependent tissues
In what circumstances is stored glycogen released from muscle?
Degraded mainly during bursts of physical activity to supply fuel for glycolysis to generate ATP for muscle contraction.
When would glucose be converted to fatty acids in the liver?
When there is excess carbohydrate intake, beyond what can be stored as glycogen
What happens to newly-synthesised fatty acids from glucose in the liver?
They are esterified with glycerol and exported from the liver to adipose tissues as TAGs via VLDL
What is the primary source of energy for the brain?
Glucose
Why are fatty acids not used by the brain for energy?
Fatty acids cannot efficiently cross the blood brain barrier
What is the energy source of red blood cells, and why?
Glucose, because they lack mitochondria so cannot break down fats by beta-oxidation
What is a characteristic of tissues that use fatty acids as fuel?
They have oxygen available for fatty acid oxidation
