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Friday, August 10, 2018

Lipid Anabolism

Lipid Anabolism (biosynthesis of fatty acid)
Category of biochemical reaction
Anabolism
Pathway location
Cytosol
Types of redox reaction
Reduction
Shuttle mechanism
Citrate shuttle
Electron carrier
NADPH


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

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 Activation of acetylcoA to malonyl coA

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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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