11.a Fatty acid synthesis Flashcards
Is there dietary requirement for fat?
There is no requirement for fat, apart from small amounts of two polyunsaturated fatty acids
Fat provides more/less kJ/gr compared to protein and Ch
More:
Fat provides 39 kJ /gram (vs protein 17 and carbohydrate 16 kJ /g)
> at relatively high levels of intake it is easy to overeat
> at very low levels of intake it is difficult to meet energy needs
Which vitamins need fat for absorption?
K,A,D,E
Four main classes of fats?
- Tri-acylglycerol = TG = triglyceride(s)
- Phospholipids
- Glycolipids
- Steroids
Triglycerides: structure?
Unsat/sat?
- Backbone of glycerol (blue)
Three fatty acids linked to it
Unsat: ouble bond (not all C atoms linked to H)
Sat: all C-carbons linked to H (C18:0)
Nomenclature: what do the following structures mean?
C18:0
C18:1 w9
C18:2 w6
From which side do you start counting the double bonds?
C18:0 = saturated fatty acid
C18:1 = mono-uns fatty acid: double bond at point 9
C18:2 w 6 = polu-uns fatty acid: first double bond at point 6
Start counting from The omega-site, which is positioned opposite from the OH-group
Unsaturated = lower/higher melting point
lower
- Fatty acids always have a(n) … unbranched/branched structure
- They have one …. group
- Animal/vegetable FA are always ….
- Micro-organism fatty acids are always ….
- Numbering from …. end to mark the functional group
- Unbranched
- Functional
- Even numbered (4026 carbons)
- Odd numbered (can be present in human tho: microbiome)
- Carbonyl end (OH)
Difference cis and trans fats?
Cis = Double bonding at the same side (/=/\ will lead to U shape )
Trans = Double bonding at opposite sides (\/=/\ will lead to _|- shape)
Most unsaturated fatty acids are in the Cis position.
Trans = often bacterial fermentation, beef, dairy
Can a poly=unsaturated fatty acid become fully saturated again? HOw?
Yes, it is hydrogenated.
Double bonds have a slightly negative charge and can attract hydrogen atoms to it.
Structure of phospholipids? Where are they typically used for/found?
Also have glycerol backbone, but instead of three fatty acids attached to it there is a rest group on the third position.
Hydrophilic group, hydrophobic tail
Used as emulsifiers, found in the Plasma membrane
What do ROS do to lipids?
Radicals can attack double bonded structure, which changes membrane structure.
How do you obtain fatty acids in the cell in a fed state?
- Triglycerides from the food: stored in chylomicrons and transported all over the body.
Can also be stored as low density lipoprotein (LDL) in the liver. - Lipoprotein lipase needed at surface of cell to extract triglycerides from chylomicrons and LDL. Fatty acids are now inside cell.
How do you obtain fatty acids inside the cell in a fasted state?
Adipose tissue. Two hormones are needed to release lipids from the adipose sites:
- adipose triglyceride lipase
- hormone sensitive lipase
Then you get free fatty acids in the blood, which you do not want, therefore they are bound to albumin. Transported into the cell.
What is then the next step for fatty acids in the cell? ATP?
Transferred to fatty acyl-CoA to neutralize the fatty acids. Always costs 2 ATP! (1 ATP – 1 AMP)
What happens to the fatty acyl-CoA?
Then, ‘spiralling structure’: stepwise removal of 2C units at a time. End up with acetyl-CoA, which can be used for ketone bodies (liver in fasting state) or oxidation in citric acid cycle.
Biggest difference breakdown acyl-CoA in peroxisome vs mito?
peroxisome: no energy yield
Cardiolipin is…
characteristics?
One of the main components of the inner mitochondrial membrane.
- Phospholipid
- One of reasons of impermeability membrane
- ~20% of lipids of IMM
- Synthesis happens within the mitochondria
Carnitine is used for..
transfer of fatty acyl CoA across the mitochondrial outer and inner membrane
(remove the CoA group and attach it to a carnitine (=acyl-carnitine), when in matrix: carnatine removed again to be reused)
Carnitine works with what type of feedback loop?
Negative feedback loop: too few oxidation of acyl CoA: it will build up, carnitine cannot be used
What does beta-oxidation mean?
= the spiral
Fatty acid oxidation by removal of 2-C units at a time with oxidation at the beta-carbon of the fatty acid
Peroxisome vs mito: which has a preference for smaller fatty acids?
mito
Step 1 of beta-oxidation starting from fatty acyl CoA?
Flavin-dependent dehydrogenation > anoyl CoA, + 1.5 ATP
Step 2 of beta-oxidation?
Hydration of enoyl CoA to hydroxylacyl CoA (addition of water across the double bond)
Step 3 of beta-oxidation?
NAD+ - dependent dehydrogenation to oxo-acyl CoA (keto-acyl CoA) , + 2.5 ATP
Step 4 beta-oxidation?
- Cleavage -> acetyl CoA + fatty acyl-CoA, then spiral can begin again
How much ATP is yielded per spiral?
4 ATP
What is the mitochondrial ATP yield of stearic acid (18:0) per mol?
- 1 Mol fatty acids = Activation -2ATP
- 8x beta-oxidation (last oxidation of 4C = 2x 2 C) = 8 * 4 = + 32 ATP
- 9 Acetyl-CoA (10 ATP per TCA cycle) = 9 * 10 = 90
90 + 32 - 2 = 120 ATP
(glucose: 30/6 = 5 ATP/C)
(FA 18:0: 120/18 = 6.7 ATP/C)
What is the difference of ATP yield in saturated vs unsaturated fatty acids?
Unsaturated fatty acids give 1.5 ATP less per double bond.
Why is the ATP yield different in uns fatty acids and sat fatty acids?
Bc the first step is skipped for uns fatty acids, which is adding of a double bond. There is already a double bond.
What is the end product for odd-numbered fatty acids? What is the ATP yield?
- Odd-numbered fatty acids end up with propionyl CoA (C3) (NOT PROPIONIC ACID)
ATP yield = 15.5 ATP
Difference propionic acid and propionyl- CoA in terms of ATP when conversing to succinyl-CoA?
Propionic acid = -3 ATP
Propionyl-CoA = -1 ATP
ATP yield C16:0 vs C18:0?
C18:0 = 120 ATP
C16:0 =
-4 ATP for -1 beta oxidation round (2C)
-10 ATP for -1 acetyl-CoA (2C)
120-14 = 106 ATP
