Lipids Flashcards
3 sources of fats
Diet
De novo biosynthesis in the liver - (starting from new in the liver)
Adipocyte stores - they can be hydrolysed to give free fatty acids and glycerol
Describe the process of lipid digestion
- there is a mix of free fatty acids, mono and diacylglycerols that are solubilised
- These then get taken up by the enterocytes within the intestine
- The lipid digestion by lipases form monoacylglycerols (MAG), diacylglycerols (DAG) and free fatty acids (FAs) which join Bile Salts, Cholesterol, Lysophosphatidic Acid and fat soluble vitamins to form mixed micelles.
- the mixed micelles are absorbed by enterocytes
- Triacylglycerols (TAGs) are resynthesised
- TAGs are packaged into chylomicrons which then enter the lymphatic system and join the circulatory system
Describe beta oxidation
- Fatty acid -> acyl coA using 2 ATPs in outer mitochondrial membrane
enzyme = acyl CoA synthethase - the Acyl CoA enters the mitochondria from the outer mitochondrial membrane by carnitine shuttle
- Fatty acyl coA oxidised and FAD is reduced to FADH2
- the molecule produced is then hydrolysed
- the product is then oxidised so NAD+ –> NADH
- remove a molecule of acetyl coA by bringing in a molecule of CoA using beta- ketothiolase
- The remaining part of fatty acyl CoA which has been shortened by two carbons then repeats the cycle
overall the original fatty acyl CoA has been shortened by 2 carbons
- during each cycle 1 NADH and 1FADH2 are formed
Overall equation for breakdown of palmitate
Palmitoyl coA + 7FAD + 7 NAD+ + 7H20 + 7CoA ——> 8 acetyl coA + 7 FADH2 + 7 NADH
When can acetyl coA from beta oxidation enter TCA?
When beta oxidation and carbohydrate metabolism are balanced as oxaloacetate is needed
Which 2 enzymes are involved in biosynthesis of lipids?
Acetyl coA carboxylase
Fatty acid synthase
What happens if acetyl coA can’t enter TCA?
Produces:
Acetoacetate
D 3 hydroxybutyrate
Acetone
Describe lipogenesis
Acetyl coA + HCO3 = malonyl coA using acetyl coA carboxylase
Transfer malonyl to ACP = malonyl ACP using malonyl-coA-ACP transferase
Transfer acetyl from acetyl coA to ACP = acetyl ACP using acetyl-coA-ACP transferase
Condensation of acetyl ACP and malonyl ACP = acetoacyl ACP
Reduction using ketoreductase
Dehydration using dehydratase
Reduction using Ebola reductase
Differences between fat metabolism and synthesis
Synthesis = ACP and uses NADP as reducing agent, happens in ER and mitochondria Metabolism = coA and uses NAD+ and FAD as reducing agents , happens in mitochondria
Lipogenesis equation
Acetyl coA + 7 malonyl coA + 14 NADP + 14H+ = palmitate + CO2 +6H2O + 8 coA + 14 NADP+
Diseases to do with lipid metabolism
Medium chain acyl coA dehydrogenase deficiency (MCADD) - autosomal recessive - part of heel prick test - no fasting - have a high carb diet Primary carnitine deficiency - autosomal recessive - carnitine supplements given
what are saturated fatty acids like?
- they are completely saturated with hydrogen (there are no double bonds) they are straight
- solids
what are unsaturated fatty acids like?
- they have double bonds which inhibit rotation, therefore, there are kinks in the chain
- these are liquids
what are adipocytes?
in mammals specialised cells called adipocytes take on the role of fatty acid storage
how does bile emulsify fats?
- bile salts are generated by the liver and stored in the gall bladder
- during digestion they are secreted into the intestine
- They emulsify fats and aid their absorption
- biles convert fats into a soluble form so that the lipases can start breaking them down
what does a lack of bile salts cause?
- Lack of bile salts causes fats to pass through the digestive tract undigested and unabsorbed resulting in steatorrhea (fatty stool)
what is the structure of bile and how does that relate to how bile works?
- bile salts have a hydrophobic face and hydrophilic face which allows the bile salts to interact with solute and triacylglyerols
- Bile salts present the hydrophobic face to the triacylglycerols and the hydrophilic face to the solvent.
what is a mixed micelle?
A Mixed Micelle forms which is a mixture of triacyl-, diacyl-, monoacylglycerols and free fatty acids.
why is having anhydrous food supplies needed?
- good way of keeping compact food stores for subsequent mobilisation when needed
- if stored as glycogen people would be much heavier as glycogen needs water to be soluble
- every gram of glycogen needs 2 grams of water
what is orlistat?
reduces fat absorption by 30% which is almost completely excreted by the faecal route - treats obesity.
compare caloric yield of fatty acids and carbohydrates?
- The caloric yield of fatty acids is about double that of carbohydrates
- More than half the body’s energy needs (including the liver but NOT the brain) comes from the oxidation of fatty acids.
how can acetyl CoA enter the TCA cycle?
- can only enter is beta oxidation and carbohydrate metabolism are balanced
- this is because oxaloacetate is needed for entry of acetyl CoA into the TCA cycle
what happens is fat breakdown predominates carbohydrate metabolism?
If fat breakdown predominates (e.g. when fasting/starving), acetyl CoA forms:
• Acetoacetate
• D-3-hydroxybutyrate
• Acetone
how many of what kind of bond generate the Acyl CoA from the fatty acid?
2 phosphoanhydride bonds
this is the same as ATP
these are needed to start off the reaction
