Learning Objectives:
• Provide a definition of a lipid.
• Describe the a generalized scheme of eukaryote fatty acid biosynthesis.
• Summarise the bioenergetics of palmitate biosynthesis.
• Describe the biosynthesis of unsaturated and long-chain fatty acids.
• Discuss the control of f...
- Lipids are a diverse group of naturally occurring molecules that are soluble in non-polar
organic solvents such as chloroform (insoluble or poorly soluble in water)
- Heterogeneous compounds and defined based on their solubility so they’re soluble in non-
polar organic solvents and insoluble in water
- They break down into the neutral lipids, polar lipids and the steroids each containing a different
type of lipid which have a different role
- Neutral lipids have a storage role in cells e.g. triacylglycerol
- Polar lipids have a structural role e.g. phospholipids
- Steroids such as cholesterol also contains sex hormones as a group
- Yellow boxes are esters of long chain fatty acids – these are the building blocks of the complex
lipids
- Two key regions of a fatty acid
- Consists of carboxyl head group and
long hydrocarbon tails
- Hydrocarbon tail made up of
repeating CH2 units terminating with
CH3
- Two variables in the fatty acids is the
length of hydrocarbon tail (CH2
number)
- Other variable is the level of
saturation of the fatty acid therefore
the number of C=C in tail
- Position of C=C vary
,- Fatty acids produced
by a cycle of reactions
- Fatty acid synthesis
takes place in the
cytosol and involves
many enzymes which
are composed of a
multi enzyme complex
- This complex is called
fatty acid synthase
and it contains many
different active sites of
enzymes
- Many intermediates
involved and mostly
linked to ACP (acetyl carrier protein) which is part of the fatty acid synthase complex
- We grow fatty acids from fatty acid precursor which is acetyl CoA which becomes acetyl ACP
(linked to carrier) and we elongate the fatty acid 2 carbons at a time pushing it through a cycle of
reactions
- Each carbon is joined via the carboxyl end
- The two carbons come from malonyl CoA which becomes malonyl ACP these are referred to as
the carbon donor and 2 carbons are added to the elongating fatty acid from malonly ACP which
is a 3C compound, since we only add 2 carbons we lose the last one as CO2
- Fatty acids go through 4 reactions in this cycle: condensation (adding carbons), reduction,
dehydration and reduction – goes from fatty acid which is x carbons to fatty acid which is x
carbons +2
Acetyl group shuttle
- Starting point for FA synthesis is
acetyl CoA
- Majority of fatty acid coA
produced in mitochondria and
the membrane is not freely
permeable to acetyl coA
- There’s a shuttle process which
can move acetyl coA out of
mitochondria into the cytoplasm
- Acetyl group shuttle:
mitochondrial Acetyl coA reacts
with oxaloacetate to form citrate using
citrate synthase
- Citrate is freely permeable to leave and move across to the cytoplasm and through the action of
a second enzyme called citrate lyase citrate is broken down to form acetyl coA and oxaloacetate
(cycled back through malate and pyruvate back into mitochondria)
,- Once acetyl CoA is in the cytosol the first reaction that occurs is to convert the 2 carbon acetyl
CoA carbon into the 3 carbon malonyl coA (carbon donor in elongation process) using enzyme
acetyl coA carboxylase.
- This is an irreversible step and it’s at this point carbon gets committed to fatty acid synthesis
- Major point of control and regulation in this pathway
Acyl carrier protein
- Next step is to link acetyl CoA and malonyl CoA to the ACP, this is done by 2 different transferase
enzymes
- ACP replaces CoA so the CoA is a product as a result
- The acetyl ACP are our 2 carbon precursor compounds for elongation and we have malonyl ACP
which is our carbon donor, the 3 carbon compound – this donates 2 carbons to our elongating
fatty acid
Condensation
- Condensation reaction where
acetyl ACP is condensed with
malonyl ACP catalysed by enzyme
β-ketoacyl synthase
- This adds 2 carbons to the
carboxyl end of the acetyl ACP
producing a 4 carbon compound
called acetoacetyl ACP
- Acetoacetyl ACP is a 4 carbon beta
ketoacyl ACP
- Products of carbon dioxide and
ACP as well
, Reduction
- Acetoaceyl ACP molecule is then reduced
for the first time to form D-3-hydroxbutryl
ACP and NADPH is oxidised to form
NADP+
- Using enzyme β-ketoacyl reductase
Dehydration
- Next is the dehydration reaction where
D-3Hydroxbutyryl ACP is dehydrated to
form water and crotonyl acp (4 carbon
compound)
- This uses enzyme dehydratase
Reduction
- The second reduction in the cycle
- Crotonyl ACP reduced to butyryl ACP
- NADPH (reductant) against oxidised to
NADP+
- Enzyme: enoyl redutase
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller laurynwills. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.74. You're not tied to anything after your purchase.
