Lecture 3- Energy storage (fat) Flashcards
lipids are stored as
triacylglycerol (TAG)
when are lipids stored as TAG
Energy intake in excess of requirement
where are TAGs stored
hydrophobic stored in anhydrous form in adipose tissue
TAG is a highly effiecient energy store
Energy content per gram twice that of carbohydrate or protein
when are TAGs utilised
Utilises in prolonged exercise, stress, starvation, during pregnancy
(under hormonal control)
adipocytes
- Around 0.1mm in diameter
- Cells expand as more fat added
- Average adult around 30 billion fat cells weighing 15kg
- Can increase in size x4 on weight gain before dividing and increasing total number of fat cells
overview of dietary TAG metabolism
- In the Small intestine fat (TAG) is converted to fatty acids and glycerol by pancreatic lipase
- fatty acids and glycerol are absorbed by intestinal epithelial cells and then reform as TAG
- TAG is transoorted to the lymph on chylomicrons and then into the blood
- in the blood TAG is either sent for storage (in the adipose) or utilisation (in the tissues–> fatty acid oxidation (energy)
lipogenesis is
fatty acid synthesis
where does lipogenesis occur
in the liver
(dietary glucose - source of carbon)
outline lipogenesis
- Glucose à pyruvate in cytoplasm’s (glycolysis)
- Pyruvate enter mitochondria and forms acetyl-CoA and OAA which then condense to form citrate
- Citrate –> cytoplasm and cleaved back to acetyl-CoA and OAA
- Acetyl-CoA carboxylase produce malonyl-CoA from acetyl-CoA
- Fatty acid synthase complex builds fatty acids by sequential addition of 2 carbon units provided by malonylCoA
requires ATP and NADPH
comparison of fatty acid synthesis and B oxidation
lipolysis
fat mobilisation
which hormone stimulates lipolysis
Hormone sensitive lipase mobilises fatty acids and glycerol from TAG
glycerol
can be utilised as a precursor of glucoseneogensis
glycerol –> glucose
fatty acids
beta-oxidation (energy production)