Fat metabolism Flashcards
(43 cards)
What are the three main categories that lipid use is defined?
1) Bilayer (phosphate bilayer)
2) Energy Stores
3) Intra and extra-cellular signalling
There are some others than are fat-soluble vitamins that have regulatory/ co-enzyme functions
How are lipids transported? Why?
Compartmentalised or transported in association with protein
-they are insoluble
What are fatty acids?
-carboxylic acids with long chain hydrocarbon side groups
Where can substantial amounts of free fatty acids be found?
Blood plasma
-transported on serum albumin to point of consumption
Where is the only place that can’t rely on fat metabolism?
The brain as the serum albumin can’t cross the cell membrane
What type of lipids are fats and oils of plants and animals?
Tricylglycerols
What types of fatty acids are attached to each carbon?
Carbon 1: Usually saturated
Carbon 2: Usually unsaturated
Carbon 3: Either
How is glycerol formed from triacyglycerols?
They are Eserified via their carboxyl groups which results in a loss of charge
What are adipocytes?
They are specialised molecules for the synthesis and storage of Triacyglycerols (TAG’s)
What is the fat content for normal humans?
21% for men
26% for women
Where is the fat stored in the body?
1) Adipocytes: - white adipose tissue, TAG’s coalesce to form oily droplets (bady’s main energy reserve)
2) Liver, but most is exported and packaged with other lipids & apoproteins to form VLDL (Very-Low-Density-Lipoproteins
When does the mobilisation of fat occur?
Occurs during times of metabolic need which is initiated by hormone-sensitive lipase
What does hormone-sensitive lipase do?
Removes the fatty acid from C-1 and/or C-3 leaving a lipid with only 1 or 2 hydrocarbon chains
-the remaining chains are removed by diacylglycerol (if 2 chainz present) or monoacylglycerol (if 1 chain is present)
When is hormone-sensitive lipase activated?
- When phosphorylated by a cyclic AMP (cAMP)
- when glucagon/epinephrine binds to cells
What is beta oxidation?
A series of catalysed reactions progressively degrading fatty acids by removing 2 Carbon units & involves the oxidation of the Beta Carbon atom to the carboxyl group
Where does beta oxidation take place and what does it produce?
Located in mitochondria
Produces AcetylCoA, NADH & FADH2
What occurs after Long Chain Fatty Acids (LCFA’s) enter the cell?
- Converted in the cytosol to its CoA derivative (known as priming)
- Catalysed by Long-Chain fatty acetyl-CoA synthatases known as Thiokinases
What is the reaction driven by?
Exergonic hydrolysis of pyrophosphate
How are acyl-CoA’s transported across an impermeable mitochondrial membrane?
- Carnitine Shuttle
- fatty acids transfer its acyl part on to carnitine forming acylcarnitine
How does acylcarnitine tranported into matrix?
Exchanged with free carnitine in opposite direction by Carnitine palmitoyltransferase I (CPT-1)
How is carnitine obtained?
In the diet from meat
-synthesised from lysine and methionine by liver and kidneys
How can carnitine deficiencies arise?
1) Liver disease
2) Malnutrition/Vegetarian diets
3) Pregnancy or Burns victims which require increased carnitine
4) Haemodialysis
How do short&medium fatty acids enter the mitochondria?
Chains with less than 12 carbons can enter without the carnitine shuttle and is not dependent on CPT-1
What are the reactions of the Fatty acyl-CoA sequence?
1) Formation of a trans-a, beta double bond
- Caused by dehydrogenation and produces FADH2
2) Hydration of the double bond to form 3-L-hydroxyacyl-CoA
3) NAD+ dependent dehydrogenation of the beta-hydroxyacyl-CoA
- forms beta-ketoacyl-CoA and NADH
4) alpha Carbon - beta Carbon cleavage in a thiolysis reaction to form Actyl-CoA and a new acyl-CoA
