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Kin 217 - November 14th - - - - - - - Slide on Dominant Dietary Fatty Acids Peroxisome – 20 C fatty acids that don’t enter mitochondrial oxidation…18 C can enter it o In times of need, structural (long) can be β-oxidized (shortened down) and shunted to break down to get energy (?) Mechanism of fat synthesis o Conversion to fat Excess carbohydrate after glycogen filled Ethanol and some amino acids General principles o Fatty acids Synthesized from acetyl-CoA (2 Carbons) Fatty acids tend to have even numbers of carbon atoms o Carbohydrates Pyruvate Acetyl-CoA o Some bacteria and plants Can make glucose from acetyl-CoA (ch 15) One of the reason you can’t find a lot of fat in plants Synthesis of malonyl-CoA o Acetyl-CoA Lacks energy to drive fatty acid syntheis WHY do we do this? Acetyl-CoA has very low energy Need energy to drive fatty acid synthesis Need energy into Acetyl-CoA…equivalent to using a Red Bull shot so that reaction that occurs is irreversibly Diagram on Malonyl CoA synthesis o Good old biotin is involved Can use carbonate to add CO2 group Malonyl-CoA o (2 carbons plus 1 carbon) o Acetyl-CoA plus a CO2 o Supplies 2-Carbons t fatty acid synthase Lose a CO2 immediately WHY? (it seems stupid that we gain a carbon just to lose 2..) Need a thermodynamically irreversible reaction Fatty Acid Synthase o Text ignores details Focus on: Acyl-carrier protein (ACP) β-ketoacyl synthase (has thiol group sulphur-hydrogen group) Ignores: - - - - - - Dimer (do you remember what this is? TWO identical subunits linked together) 7 catalytic sites + acyl-carrier protein (ACP) Mentions: Bacteria have separate enzymes Animas have a enzyme complex Structure of fatty acid synthase (diagram) o Top half is one unit, bottom is the other unit (dimmer) Acyl carrier protein (ACP) o β-oxidation CoA is the carrier o Fatty acid synthesis Acyl group carrier is ACP Contains part of the CoA molecule Homology in acyl carrier group and CoA molecule (?) Acetyl CoA slide… Fig 14.1 o Priming reaction at first Reactions catalyzed by fatty acid synthase (Diagram) o Two business enzymes o Ying-yang…fully activated at both ends of enzymes o Why would mammals benefit from 7 sites? Tends to be a little more efficient The players are all together, substrate there Fig 14.2 o The 3 steps missing from the cycle The reductive steps in fatty acid synthesis o The reductant is NADPH rather than NADH! o Difference between NADPH and NADH? Extra phosphate group on NADPH What is NADP+? o Extra phosphate Identification signal Reductive power for energy use Reductive power for synthesis o NAD+ and NADP+ reduction occur using separate mechanisms Compartmentalization Where does fatty acid synthesis take place? o Fatty acids synthesis to palmitate Cytosol o Acetyl-CoA formed in mitochondria Restrictions on getting mitchondria into cytosol for fatty acid synthesis (?) Fig 12.10 o What enzyme? Pyruvate dehydrogenase - - - - - Making acetyl-CoA inside mitochondria Fig 14.4 o How do we get acetyl-CoA outside mitochondria? o Form citrate with Citrate synthase that can be shunted outside mitochondria Need ATP to break down citrate to make acetyl-CoA Not a bad thing of having to use ATP when we have a situation of excess storage/energy (?) o Pyruvate can re-enter mitchondria o Somehow, we need to make NADPH Oxaloacetate back to pyruvate Sacrificing NADH to form NADPH (?) Fig 14.3 Metabolism of pyruvate o Pyruvate carboxylase reaction o Topping up mechanism(?) NADPH o NADPH from “malic enzyme” ½ reducing power required for fatty acid synthesis Other ½ form pentose phosphate pathway (ch 17) o Linked to excess glucose supply (NADPH will be more abundant when energy supply is abundant) Unsaturated Fatty Acid Synthesis o Acetyl-CoA 16:0 (fairly important fatty acids) How do we get other fatty acids? Elongase reaction (gain 2 to get 18:0) Desaturases.. ∆9 Desaturase can add double bond into saturated fatty acid length to give 18:1n-9 (something about alpha and omega ends????) How do we make polyunsaturated fatty acids? Need a ∆12 desaturase…add double bond 12 carbons from alpha end…6 from the omega end ∆12 and ∆15 don’t occur in mammals (only in plants and bacteria)… Where do we get it then? DIET! We can’t synthesize 18:2n-6 and 19:3n-3 We can make 16:1n-7… PUFA Biosynthesis o Once we make 18:2n-6, we can add or take away carbons from 18C precursor o But humans depend on getting longer fats from the diet… o Cats lack ∆5 Desaturase Carnivores don’t need to synthesize long fatty acids because they’re eating a lot of meat (?) o 18:2, 18:3, essential fatty acids! WE can synthesize everything else…dry skin is a first sign of fatty acid deficiency If we don’t have these 2 in our diet, 18:2n9 can enter and be worked on by to get a 23n9 (?)… Peroxisome – remember all fatty acids attached to a CoA group