6 - Lipid Metabolism Flashcards
(27 cards)
What is the structure of a fatty acid?
a molecule containing a hydrocarbon chain with a carboxylic acid group (hydrophilic) at the end
Give an example of a saturated FA
stearic acid
Give an example of an unsaturated FA
oleic acid
How are fatty acids usually stored within a cel?
as triacylglycerols (TAGs)
Triacylglycerols come together to form _____
lipid droplets
In mammals, what cells store fatty acids?
adipocytes
Where are bile slats produced and stored?
Where are they secreted into?
produced in the liver
stored in the gall bladder
secreted into small intestine
What is the role of bile salts?
to emulsify fats
What does a lack of bile salts result in?
steatorrhoea
because fat passes through the digestive tract undigested and unabsorbed
What easily allows bile salts to interact with TAGs and solute/solvent?
hydrophilic and hydrophobic faces
Describe emulsification by bile
- bile salts present the hydrophobic face to TAGs and the hydrophilic face to the solvent
- this breaks the lipid droplets into small droplets in ‘a soluble form’, increasing the SA
- pancreatic lipases break the TAGs down
- results in (TAGs), DAGs, MAGs and FFAs
How are mixed micelles formed from soluble, digested lipid droplets?
What happens to them after they have formed?
- the DAGs, MAGs and FFAs join bile salts, cholesterol, lysophosphatidic acid and fat soluble vitamins to form mixed micelles
- they are then absorbed by enterocytes in the small intestine
- TAGs are resynthesised and packaged into chylomicrons
(chylomicrons = TAGs + other proteins + apoproteins) - chylomicrons enter the circulation via lymph
What is orlistat?
a potent inhibitor of gastric and pancreatic lipases
designed to treat obesity
reduced fat absorption by 30% (excited by faecal route)
Which body part does not use energy from the β-oxidation/fats?
Where does it get its energy from instead?
the brain - uses energy from ketone bodies when glucose supply is low
Where does β-oxidation occur in a cell?
What does it produce?
in the mitochondria
results in the formation of acetyl CoA
What is the first step in β-oxidation?
fatty acids —–> acyl CoA
enzyme = acyl CoA synthetase
NOTE: ATP —> AMP (2 high energy bonds are used)
Where dies the first step in β-oxidation take place?
on the outer mitochondrial membrane
How do the products of the first step in β-oxidation get into the mitochondria?
What are the enzymes used in this process? What do they do?
carnitine shuttle
translocase - to carry carnitine and acylcarnitine across the inner mitochondrial membrane
carnitine acyltransferase I/II - to transfer the acyl group
Describe the β-oxidation cycle
What is the overall result of this?
OHOT
1- fatty acyl CoA is oxidised (FAD—>FADH2)
2- hydrolysis
3- oxidation (NAD+—>NADH)
4- thiolysis (a molecule of acetyl CoA cleaved off by bringing in CoA and using β-ketothiolase)
the original fatty acyl CoA has been shorted by 2 carbons and a module of acyl CoA has been produced
During each cycle of β-oxidation, how many NADH and FADH2 are produced?
1 NADH
1 FADH2
KEY POINT: Acetyl CoA formed from β-oxidation can only enter the TCA cycle if β-oxidation and carbohydrate metabolism are balanced.
Why is this?
because OXALOACETATE is needed for entry of Acetyl CoA into the TCA cycle.
If fat breakdown predominates (e.g. when fasting/starving), what does acetyl CoA form instead?
KETONE BODIES
- Acetoacetate
- D-3-hydroxybutyrate
- Acetone
How many ATP are produced from palmitate β-oxidation?
129
Where does lipogenesis take place?
in the liver, in the cytoplasm of cells
