Fatty Acid Metabolism Flashcards
Why do we store fat ?
- one of the main energy stores
- reduced and non polar : has a low osmotic pull and so there is little water associated with it giving it a small storage volume
- high energy yield : 2.5x more than carbohydrates and proteins
Describe the different uses of fat for the body
- needed for lipid synthesis by the body
- lipids are important signalling molecules
- lipids are needed for the storage of fat soluble vitamins
- lipids are important for the calcification of dentine
What are the 2 types of fat storage tissues ?
- white fat (adipose tissue)
- brown fat
Describe white fat
- TAG is sequestered in cells
- it is a storage organ
- clustered in certain locations
- if it is stored in ectopic locations it is called visceral fat and this increases the risk of type 2 diabetes
Describe brown fat
- it is found close to the heart
- contains TAG and mitochondria
- it is an active metabolic organ involved in heat generation
- found in infants and hibernating animals
Where does the digestion and absorption of dietary lipids take place ?
Most digestion and absorption takes place in the small intestine
Briefly describe how lipids are digested
- pancreatic lipases break the ester bonds to yield free fatty acids and mono acyl glycerides
- bile salts aid digestion by creating an emulsion
How are short chain fatty acids absorbed ?
Short chain fatty acids which are less than 12C can enter the blood stream directly
Describe how longer chain fatty acids are digested and absorbed
1) longer chain fatty acids are resynthesized into triacylglycerides in the endoplasmic reticulum of mucosal cells
2) TAGs are then packaged into lipoprotein transport particles known as chylomicrons
3) chylomicrons are released into the lymph before entering the blood stream
4) they then travel to adipose tissue for storage
5) chylomicron remnants travel to the liver for processing
Describe the utilisation of fatty acids as fuels
this is a 3 stage process :
1) mobilisation of lipids to fatty acids and glycerol in fat cells prior to transportation to energy requiring tissues - lipolysis
2) activation of the fatty acids and transport to mitochondria in the energy requiring tissues
3) stepwise processing into acetyl CoA prior to degradation in central metabolism
Describe lipolysis (stage 1)
1) perilipin which is a protein found on the outside of lipid droplets is activated by phosphorylation by protein kinase A and this changes the conformation of the proteins so the enzyme hormone sensitive lipase moves closer to the lipid droplet
2) hormone sensitive lipase will recognise signals when fats are being released from their stores
3) glucagon will send a signal cascade
4) this activates cyclic AMP which activates protein kinase A
5) hormone sensitive lipase will then release fatty acids and glycerol from the fat droplet
6) glycerol can enter the bloodstream and serum albumen will transport fatty acids to the tissues
What stimulates and inhibits lipolysis ?
stimulated by :
- adrenaline
- noradrenaline
- glucagon
- ACTH (pituitary hormone)
inhibited by :
- insulin
Describe activation and transport (stage 2)
step 1 :
- activation occurs by the synthesis of Acyl CoA
- this requires an input of energy
- requires coenzyme A
- mediated by Acyl CoA synthetase
step 2 :
- carnitine will allow the fatty acids to enter the mitochondria from the cytosol
- it is a small molecule located in the inner mitochondrial membrane
- it is primarily used for transportation of long chain Acyl CoA molecules
Where are fatty acids broken down ?
in the mitochondria
Describe the beta oxidation pathway (stage 3)
- saturated acyl CoA is degraded sequentially by the beta oxidation pathway (this means 2C are lost per round)
- each round produces :
- FADH2 = 1.5 ATP
- NADH = 2.5 ATP
- Acetyl CoA = 10 ATP
- an acyl CoA which is 16C in length would yield 108 molecules of ATP (8 Acetyl CoA + 7 FADH2 + 7NADH)