Category
of biochemical reaction
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Anabolism
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Pathway location
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Cytosol
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Types of redox reaction
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Reduction
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Shuttle mechanism
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Citrate shuttle
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Electron carrier
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NADPH
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FATTY ACID SYNTHESIS
- reduction process that build up the hydrocarbon chain of fatty acids utilizing activated acyl unit and malonyl unit.
- occur in cytoplasm
- catalyzed by fatty acid synthase containing 7 catalytic sites.
- incorporates carbon atoms from acetyl coA into growing fatty acid
- reverse process of degragation of fatty acid
condensation 👉 reduction 👉dehydration 👉reduction
- driven by the release of CO2 in a decarboxylation step.
- energetically unfavourable process
- reduction procss involved NADPH
- extension of fatty acid chain stops at 16C (saturated palmitate)
Location of acetyl coA into cytosol
🠟
Activation of acetylcoA to malonyl coA
🠟
Synthesis of fatty
acid chain via addition of activated acetyl coA
LOCATION OF ACETYL coA INTO CYTOSOL
CITRATE SHUTTLE : Acetyl CoA transporter
ACETYL CoA ➖ CITRATE
IN CYTOSOL- CITRATE ➖ ACETYL CoA
so now here is a little bit of calculation, in this process we need to produce 16C
- in every 1 acetyl-coA transported into the cytosol, 1 NADPH form
- here we are making palmitate (16C), so we need 8 acetyl-coA(2C)
- 8 transported acetyl coA= 8 NADPH
- the other 6 NADPH will be produced by THE PENTOSE PHOSPHATE PATHWAY
ACTIVATION OF ACETYL CoA TO MALONYL COA
- initiation of fatty acid synthesi
- formation of malonyl coA trough the irreversible carboxylation of acetyl coA
- a co2 is attached to acetyl coA producing a 3C molecule
SYNTHESIS OF FATTY ACID CHAIN VIA THE ADDITION OF ACTIVATED ACETYL-COA
This elongation of fatty acid chain start with formation of malonyl ACP and acetyl ACP
FATTY ACID SYNTHESIS
condensation
- the acetyl group moves from cystein residue onto malonate group on ACP
- product : acetoacetyl attached to ACP, CO2 released
reduction
- acetoacetyl is tranformed to D-3 hydroxybutyryl by con verting the carbonyl group into alcohol group
- reducing agent : NADPH + H+ 🠆 NADP+
- catalyzing enzyme : 𝞫-ketoacyl-ACP reductase
dehydration
- removal of hydroxyl group as H2O and formatiom pf C=C
- catalyzed by 3-hydroxyaxyl-ACP dehydratase
reduction by NADPH
- butyryl group is generated on ACP
- NADPH reduced the C=C because the ultimate fatty acid chain produced is a saturated fatty acid
- this completes the first elongation process containing 4C carbon.
the next 6 cycle produced 2C, total cycle is 7. palmitate (16C) is produced.
CHOLESTEROL BIOSYNTHESIS
- cholesterol only synthesize in animal
- cholesterol and steroid are synthesized from 2 acetyl-coA
- ISOPRENE units are the key to the biosynthesis of steroid and other biomolcules
- cholesterol is precursor for bile salts and a number of steroid hormones
LIPOPROTEIN
DETAILS OF HOW THE LIPIDS ARE TRANSPORTED IN THE BLOOD STREAM
CHOLESTEROL CAN LEAD TO THE HEART DISEASE
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