Chapter 14

生物化学精品课程

Chapter 14Chapter 14

Lipid BiosynthesisLipid Biosynthesis

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1. Fatty acids;

2. Eicosanoids类花生酸类 ;

3. Triacylglycerols;

4. Membrane phospholipids膜磷脂 ;

5. Cholesterol, steroids, and isoprenoids;


1. Fatty acid synthesis takes a different pathway from its degradation

Occurs in the cytosol (chloroplasts in plants).Acetyl-CoA provides the first two carbons, which is elongated

by sequential addition of two-carbon units donated from malonyl-CoA丙二酰 .

Intermediates are attached to the -SH groups of an acyl carrier protein (ACP).

NADPH is the reductant.The enzymes are associated as a multi-enzyme complex or

even being in one polypeptide chain in higher organisms (fatty acid synthase).

Elongation by the fatty acid synthase complex stops upon formation of palmitate (C16), further elongation and desaturation are carried out by other enzyme systems.

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2. Malonyl-CoA is formed from acetyl-CoA and bicarbonate

Salih Wakil discovered that HCO3- is required for fatty acid

synthesis.

Acetyl-CoA carboxylase (being trimeric in bacteria, monomeric in

animals and both in plants) catalyzes this carboxylation reaction.

The enzyme has three functional parts: a biotin carboxyl carrier

protein, BCCP; an ATP-dependent biotin carboxylase, BC羧化酶 ;

and a transcarboxylase (carboxyl transferase, CT)羧基转移酶 .

The enzyme exemplifies a ping-pong reaction mechanism.

This irreversible reaction commits acetyl-CoA to fatty acid

synthesis.

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Acetyl-CoA carboxylase catalyzes the two-step carboxylation reaction of acetyl-CoA in two active sites.

biotin carboxylase

Trans-carboxylase

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3. The acetyl and malony groups are first transferred to two –SH groups of the fatty acid synthase complex

The acetyl group of acetyl-CoA is first transferred to the –

SH group of a Cys residue on the β-ketoacyl-ACP synthase

(KS) in a reaction catalyzed by acetyl-CoA-ACP

transacetylase (AT,乙酰基转移酶 ).

The malonyl group is transferred from malonyl-CoA to the

–SH group of the 4`-phosphopantetheine磷酸泛酰巯基乙胺 covalently attached to a Ser residue of the acyl carrier

protein (ACP).

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The acyl carrier protein (ACP) is very similar to CoA (thus can be regarded as “macro CoA”)

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4. Fatty acids are synthesized by a repeating four-step reaction sequence

In the condensation reaction (step 1), catalyzed by β-ketoacyl-ACP

酮脂酰 synthase, the methylene亚甲基 group of malonyl丙二酰 -

CoA (linked to ACP) undergoes a nucleophilic亲核的 attack on

the carbonyl羰基 carbon of the acetyl group linked to KS, forming

the β-ketobutyryl-ACP with simultaneous elimination of CO2.

the β -ketobutyryl-ACP is then reduced to D- β -hydroxybutyryl-

ACP (step 2), using NADPH and the β -ketobutyryl-ACP reductase

(KR).

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A water molecule is then removed from the β -hydroxybutyryl-

ACP to produce trans-2-butenoyl-ACP in a reaction catalyzed

by β-hydroxybutyryl-ACP dehydratase (step 3).

A further reduction (step 4), also using NADPH, of the carbon-

carbon double in trans-2-butenoyl-ACP, catalyzed by enoyl-

ACP reductase produces a saturated acyl on ACP (butyryl-

ACP).

The butyryl group is then transferred to the Cys –SH group of β

-ketoacyl-ACP synthase for another round of four reactions,

which will extend the chain by two more carbons.


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Seven rounds of the four-step lengthening reactions produces

palmitoyl软脂酰 -ACP, which will be hydrolyzed to release a

free palmitate.

The flexible 4`-phosphopantetheine磷酸泛酰巯基乙胺 group

covalently attached to ACP is believed to act as a switch arm to

move the intermediates from one active site to the next on the

enzyme complex (i.e., the substrates are channeled).

A total of 7 ATP and 14 NADPH will be consumed for making

one palmitate molecule.


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Table Proteins of the fatty acid synthase complex of E.coli

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5. The seven activities of fatty acid synthesis from different organisms have different level of integration

Each activity resides in a separate polypeptide chain in bacteria

and higher plants.

The seven activities reside in two separate polypeptide chains,

with the synthase present as do decamers (α6β 6, yeast).

The seven activities reside in one large polypeptide chain in

vertebrates, with the synthase present as dimers.

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The seven activities of fatty acid synthase are integrated todifferent levels in different organisms.

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6. Fatty acid synthesis occurs in cellular compartments having a high NADPH/NADP+ ratio

NAD and NADP have selected for functioning as electron carriers in oxidative catablism and reductive anabolism respectively.

In the hepatocytes肝细胞 and adipocytes脂细胞 , NADPH is mainly produced in the cytosol via the pentose phosphate pathway and by the malic苹果的enzyme.

In photosynthetic plants, fatty acid synthesis occur in the chloroplast stroma, using NADPH made from photophosphorylation.

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NADPH in the cytosol of animal cells is largely produced by the oxidative decarboxylation of malate and the pentose

phosphate pathway

Malic enzyme Pentose phosphate

pathway

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7. The acetyl groups of the mitochondrion are transported into the cytosol in the form of citrate

The acetyl-CoA molecules are made from glucose and amino acids in mitochondria.

The are shuttled into the cytosol in the form of citrate via the citrate transporter of the inner membrane.

Acetyl-CoA is regenerated by the action of ATP-dependent citrate lyase in the cytosol.

Oxaloacetate is shuttled back into the mitochondria as malate or pyruvate.

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7. The acetyl groups of the mitochondrion are transported into the cytosol in the form of citrate

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8. The rate of fatty acid biosynthesis is controlled by acetyl-CoA carboxylase

Excess fuel is generally converted to fatty acids/triacylglycerol

for longer term storage.

Acetyl-CoA carboxylase, catalyzing the committing and rate-

limiting step of fatty acid synthesis, is allosterically inhibited by

palmitoyl-CoA and activated by citrate.

Glucagon高血糖素 and epinephrine肾上腺素 triggers the

phosphorylation and disassociation of the polymeric enzyme

subunits, which inactivates the enzyme.

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8. The rate of fatty acid biosynthesis is controlled by acetyl-CoA carboxylase

Citrate partially activate the phosphorylated acetyl-CoA

carboxylase (similar to how AMP partially active the

dephosphorylated glycogen phosphorylase).

In plants, acetyl-CoA carboxylase is activated by a increase of

Mg 2+ concentration and decrease of H+ concentration that

accompany illumination.

(Malonyl-CoA inhibits carnitine acyltransferase I)

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Acetyl-CoA carboxylase is regulated by allosteric effectors and reversible phosphorylation

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Citrate partially activate the phosphorylated acetyl-CoA carboxylase

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9. Palmitate can be further elongated and desaturated in smooth ER

Palmitoyl-CoA can be further elongated by the fatty acid elongation system present mainly in the smooth endoplasmic reticulum, with two-carbon units also donated by malonyl-CoA.

Palmitoyl-CoA and Stearoyl-CoA can be desaturated between C-9 and C-10 to produce palmitoleate, 16:1(9), and oleate, 18:1(9) respectively.

The double bonds are introduced by the catalysis of fatty acyl-CoA desaturase (a mixed-function oxidase), where both the fatty acyl group and NADPH are oxidized by O2.

The electrons of NADPH are transferred to O2 via Cyt b5 reductase and cytochrome b5.

Further desaturation of oleate occur on phosphatidylcholine and is catalyzed by another desaturase, which is present only in plant cells.

Linoleate and linolenate, needed to make other polyunsaturated fatty acids like arachidonate are essential fatty acids for mammals.

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Palmitate is the Precursor for the biosynthesis of Palmitate is the Precursor for the biosynthesis of other fatty acids other fatty acids

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Fatty acyl-CoA is desaturated (oxidized) by O2 and NADPH.

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Oleate can be desaturated on Phosphatidylcholine(often attaching to C-2) to form linoleate and linolenate

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10. Eicosanoids are derived from arachidonate, 20:4 (5,8,11,14)

The arachidonate (花生四烯酸 ) is first cleaved off from membrane phospholipids by phospolipase A2, in response

to hormonal or other stimuli.

Arachidonate is then converted to PGH2 by the catalysis

of the bifunctional cyclooxygenase (COX): the cyclooxygenase activity converts arachidonate to PGG2;

the peroxidase activity then converts PGG2 to PGH2.

PGH2 is the immediate precursor of other prostaglandins

and thromboxanes.

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10. Eicosanoids are derived from arachidonate, 20:4 (5,8,11,14)

Aspirin (acetylsalicylate) irreversibly inhibits the cyclooxygenase by acetylating an active site Ser, thus blocking the synthesis of prostglandins and thromboxanes; Ibuprofen also inhibit the same enzyme.

Arachidonate can also be modified by adding hydroperoxy groups at various positions to form various hydroperoxyeicosatetraenoates (HPETEs) in reactions catalyzed by various lipooxygenases with the incorporation of O2.

The HPETEs will be further converted to leukotrienes (白细胞三烯 ).

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Prostaglandins and thromboxanes are synthesized from arachidonate

Cyclooxygenaseactivity of COX

Peroxidaseactivity of COX

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The dimeric bifunctional cyclooxygenase(COX-1)

flurbiprofen

Ser530

Heme for the peroxidaseactive site

Tyr385, a key residue for the cyclooxygenase activity

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11. Newly synthesized fatty acids have mainly two alternative fates in cells

Fate I: be incorporated into triacylglycerols as a form

to store metabolic energy in long terms.

Fate II: be incorporated into membrane phospholipids

(during rapid growth).

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12. Phosphatidic acid is the common precursor for the syntheses of both triacylglycerols and glycerophospholipids

Phosphatidic acid (or diacylglycerol 3-phosphate) is

made by transferring two acyl groups from two acyl-

CoAs to L-glycerol 3-phosphate, which is derived

from either glycerol or dihydroxyacetone phosphate.

A phosphatidic acid is converted to a triacylglycerol

via a dephosphorylation reaction (catalyzed by

phosphatidic acid phosphatase) and a acyl

transferring reaction.

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Phosphatidic acid is derived from L-glycerol 3-Phosphatidic acid is derived from L-glycerol 3- phosphate and two acyl-CoAs. phosphate and two acyl-CoAs.

Often saturatedOften unsaturated

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13. Insulin stimulates conversion of dietary carbohydrates/proteins into fat

Diabetes patients due to lack of insulin would neither be able to use glucose properly, nor to synthesize fatty acids from carbohydrates and amino acids.

They show increased rates of fatty acid oxidation and ketone body formation, thus losing weight.

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14. Two strategies are taken for converting phosphatidic acid to glycerophospholipid

Eugene Kennedy revealed in 1960s that either the –OH group of the diacylglycerol (strategy 1) or that of the polar head (strategy II) is first activated by attaching to cytidine nucleotide.

The CMP moiety is displaced by the other –OH group in a nucleophilic attack reaction to synthesize a glycerophospholipid.

Both strategies are used in eukaryotic cells, but only strategy I is use in bacterial cells.

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Eukaryotic cells use both strategies (occurring on sER and inner membrane of mitochondria)

Bacteria mainly usethis strategy

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Phospholipid synthesis in E. coli employs CDP-diacylglcerol

phosphatasedecarboxylase

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15. Acidic (anionic) phospholipids in eukaryotic cells are synthesized using CDP-diacylglycerol

These include phosphatidylglycerol, cardiolipin, phosphatidylinositol, phosphatidylserine.

eukaryotic cardiolipin is synthesized from one phosphatidylglycerol and one CDP-diacylglycerol (from two phosphatidylglycerols in bacteria).

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16. Phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) are often made from the salvage (reuse) pathway in

mammals

Diet choline and ethanolamine are first converted to CDP-choline and CDP-ethanolamine after an initial phosphorylation step.

The CMP moiety is then replaced by a diacylglycerol, forming PC and PE.

Phosphatidylserine (PS) is often made from PE by a head exchange reaction (reversible).

PC can be made from PE by three methylation reactions using

S-adenosylmethionine (adoMet) in the liver cells.

PS can also be converted to PE by a decarboxylation reaction.

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PC and PE are made from the salvage pathway in mammals

((ethanolamine)ethanolamine)

(Phosphoethanolamine)(Phosphoethanolamine)

(CDP-ethanolamine)(CDP-ethanolamine)

(Phosphatidylthanolamine)(Phosphatidylthanolamine)

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The synthesis of PE, PC, PS in eukaryotic cells.The synthesis of PE, PC, PS in eukaryotic cells.

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17. The synthesis of ether lipids involves a displacement of fatty acyl by fatty alcohol step and a desaturation step

Both plasmalogen (缩醛磷脂 ) and platelet-activating factor are made using this pathway.

The acyl group on 1-acyldihydroxyacetone 3-phosphate is replaced by a long chain alcohol group to form the ether linkage.

The double bond in plasmalogen is introduced at the end by the catalysis of a mixed-funciton oxidase.

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Synthesis of the ether lipids (Synthesis of the ether lipids ( 醚脂类醚脂类））

1-alkylglycerol 3-phosphate1-alkylglycerol 3-phosphate

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18. The sphingosine backbone of spingolipids is derived from palmitoyl-CoA and Ser

Palmitoyl-CoA condenses with serine (PLP is needed for decarboxylate serine) to form b-ketosphinganine, which is then reduced to sphinganine (二氢鞘氨醇 ).

Sphinganine is then acylated and desaturated to form ceramide (containing sphingosine).

Addition of sugar(s) or phosphocholine heads leads to the synthesis of cerebroside, gangliosides, or sphingomyelin.

The ways for the membrane lipids (glycerolphospholipids and spingolipids) synthesized at smooth endoplasmic reticulum or inner membrane of Mitochondria to be transported to specific cellular locations are not well understood yet.

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Spingolipid synthesis begins with the condensation between palmitoyl-CoA and Ser.

(not CDP-choline!)

A glycolipid, not aphospholipidPLP

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19. Radioisotope tracer experiments revealed that all the 27 carbons of cholesterol is derived from acetyl-CoA

The origin of the carbon atoms of cholesterol was deduced from tracer experiments where either with the methyl carbon or the carboxyl carbon in acetate is labeled with 14C (1940s).

The pattern of labeling provided the blueprint for revealing the detail enzymatic steps for cholesterol biosynthesis occurring in mammals.

The 30-carbon squalene (of six isoprene units) and later on mevalonate were found to be intermediates of cholesterol biosynthesis.

The biosynthetic pathway of cholesterol, being the most complex known, was elucidated mainly by Konrad Bloch and Feodor Lynen in the 1950s.

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The carbon origins of cholesterol as revealed byradioisotope labeling studies.

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The Nobel Prize in Physiology or Medicine, 1964

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20. The cholesterol biosynthesis pathway can be divided into four stages

Stage I: three acetyl-CoA molecules condense to form the 6-carbon mevalonate (甲羟戊酸 ).

Stage II: mevalonate is converted to activated 5-carbon isoprene (异戊二烯 ) units.

Stage III: Six isoprene units condense to form the linear 30-carbon squalene(鲨烯 ).

Stage IV: The linear squalene is cyclized to form a four-ring structure, which is eventually converted to the 27-carbon cholesterol through a series of complicated reactions.

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Reactions assembling cholesterol from 18 molecules of acetyl-CoA can be divided into four stages.

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21. Mevalonate commits the acetyl groups for cholesterol synthesis

One molecule of β-hydroxy-b-methylglutaryl-CoA (HMG-CoA) is formed from three acetyl-CoA molecules in the cytosol via the same reactions as occurring in mitochondria for ketone body formation.

HMG-CoA reductase (an integrated membrane protein in the smooth ER) catalyzes the irreversible reduction of HMG-CoA (using two molecules of NADPH) to form mevalonate: committing the acetyl groups for cholesterol synthesis (thus being a major regulation step).

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One mevalonate is synthesized from three acetyl-One mevalonate is synthesized from three acetyl-CoA molecules.CoA molecules.

HMG-CoA lyase in mitochondriaHMG-CoA lyase in mitochondriaAcetyl-CoA + acetoacetate

The irreversible committing step for The irreversible committing step for cholesterol biosynthesischolesterol biosynthesis

HMG-CoAReductaseIn cytosol

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22. Two activated isoprenes are formed from mavelonate after going through three phosphorylation steps

Three phosphate groups are transferred from three

ATP molecules to mevalonate to form 3-phospho-5-

pyrophosphomevalonate.

The leaving of both the carboxyl and the 3-phosphate

groups leads to the formation of 3-isopentenyl

pyrophosphate.

3-Isopentenyl pyrophosphate is isomerized to form

the second activated isoprene: dimethylallyl

pyrophosphate.

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Two activated isoprenes are formed from Two activated isoprenes are formed from mavelonate. mavelonate.

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23. The 30-carbon linear squalene is formed from the condensation of six activated isoprene units

A dimethylallylpyrophosphate is joined to an isopentenylpyrophosphate (head-to-tail) to form the 10-carbon geranyl pyrophosphate.

A geranyl pyrophosphate is joined to another 3-isopentenyl pyrophosphate (head-to-tail) to form the 15-carbon farnesyl pyrophosphate(法呢基焦磷酸 ).

Two farnesyl pyrophosphate join (head-to-head) to form the 30-carbon squalene.

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Farnesyl pyrophosphate is formed from three activated isoprene units

15-carbon

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Squalene is formed from the condensation of two farnesyl pyrophosphates

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24. The rings of cholesterol are formed via a concerted reaction across four double bonds of the linear squalene

epoxide intermediate

Squalene 2,3-epoxide, is first formed in a reaction catalyzed by squalene monooxygenase using O2 and NADPH.

Concerted movement of electrons through four double bonds and the migration of two methyl groups generates lanosterol (羊毛固醇 ).

Lanosterol is converted to cholesterol via about 20 enzymatic reactions including many double bond reduction and demethylations.

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25. Cholesterols made in vertebrate livers can be converted to bile acids and cholesterol esters before exporting

Cholesterol can be converted to bile acids and bile

salts, which will be secreted to the intestine for

emulsifying lipids.

Cholesterol can also be converted to the more

hydrophobic cholesterol esters, which will be stored

in the liver or transported to other tissues after being

incorporated into lipoprotein particles.

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Cholesterol can be converted to bile acids (salts) Cholesterol can be converted to bile acids (salts) ：： glycocholate and taurocholate glycocholate and taurocholate

牛黄胆酸盐

（甘胆酸盐）

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Acyl-CoA-Cholesteryl acyl transferase (ACAT) catalyzes the addition of an acyl group to the hydroxyl group of cholesterol

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26. Lipids (including cholesterols) are transported in the vertebrate plasmia as various lipoprotein particles

The different lipoprotein particles, having different combinations of lipids and apolipoproteins, can be separated by untracentrifugation due to different densities and sizes.

The human plasma lipoproteins include chylomicrons (which transports lipids from intestine to various tissues), VLDL (very low density lipoproteins), LDL(Low density lipoproteins), HDL (high density lipoproteins).

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At least nine apolipoproteins (named as apo A, B, C, D, E) have been revealed in human, which act as signals to target the lipoprotein particles to various tissues or activating enzymes that will act on the lipoproteins.

Endogenous lipids made in liver are transported to other tissues as VLDL particles (~ 87% lipids and 12% proteins).

The apoC-II protein in VLDL activates the lipoprotein lipase in muscle and adipocyte tissues, thus releasing free fatty acids there.


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Some VLDL remnants is then converted to LDL (with 23% proteins and 75% lipids) and with the others being absorbed by the liver cells via receptor-mediated endocytosis.

LDL delivers cholesterols to extrahepatic tissues, where its apoB-100 protein (4636 residues) is recognized by specific LDL receptors and LDL is endocytosed.

HDL, with its precursors formed in the liver or intestine cells, collects the cholesterols in the plasma and deliver them to the liver cells.

(A negative correlation between blood HDL level and arterial diseases has been observed.)


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Lipids are transported as various lipoprotein particles in vertebrate plasma

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LDL is uptaken by cells via the LDL receptorsLDL is uptaken by cells via the LDL receptors

LDL receptors are recycled to the cell surfaces

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27. The de novo synthesis of cholesterol is regulated to complement dietary intake

HMG-CoA reductase, catalyzing the rate-limiting step of the de novo cholesterol synthesis, has an activity variable over 100 fold!

An yet characterized sterol promotes proteolytic degradation of HMG-CoA reductase and inhibits the transcription of the genes of HMG-CoA reductase and LDL receptor.

Hormones (insulin and glucagon) regulate the activity of the HMG-CoA reductase via reversible phosphorylation.

Genetic defect of the LDL receptor was found to cause the familial hypercholesterolemia and atherosclerosis: the LDL cholesterols can not enter the cells, while de novo synthesis continues despite the high cholesterol level in the blood.

Mevalonate analogs (e.g., compactin and lovastatin) can be used to treat patients with familial hypercholesterolemia.

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The de novo synthesis of cholesterol is regulated to complement the dietary uptake

(For storage)(For storage)

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The mevalonate analogs are used to treat hypercholesterolemia patients.

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The Nobel Prize in Physiology or Medicine, 1985

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28. Pregnenolone, the common precursor of all steroid hormones, is derived from cholesterol

The tail chain of cholesterol is first hydroxylated at C20

and C22, and then cleaved between these two carbons to

remove a 6-carbon unit, forming pregnenolone(孕烯醇酮 ).

The hydroxylation is catalyzed by cytochrome P450 monooxygenases (a mitochondrial enzyme) that utilize NADPH and O2.

Cytochrome P450 is a large family of enzymes with different substrate specificity, hydroxylates many hydrocarbon chains.

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Prognenolone, the common precursor of steroid hormones, is synthesized from cholesterol

cytochrome P450monooxygenases

Desmolase碳链裂解酶

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29. All steroid hormones are derived from cholesterol

Progesterone (孕酮 ) is synthesized from pregnenolone by oxidizing the 3-OH group and the isomerization of the double bond (from 5 to 4 position).

Cortisol (a major glucocorticoid) is synthesized from progesterone by hydroxylation at C-17, C-21, and C-11.

Aldosterone (a mineralocorticoid) is synthesized from progesterone by hydroxylation at C-21, C-11, and oxidation of C-18 to an aldehyde.

Testosterone (an androgen, or male hormone) is synthesized from progesterone by the removal of 2-carbon unit and hydroxylation at C-17.

Estradiol ( an estrogen, or female hormone) is synthesized from testosterone by the removal of C-19 and formation of the aromatic A ring.

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Progesterone is synthesized from pregnenolone by oxidizing the 3-OH group and the isomerization of the double bond

from 5 to 4 position

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Cortisol and aldosterone are synthesized from progesterone by several oxygenation reactions (forming hydroxyl and

aldehyde groups)

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Testosterone is synthesized from progesterone by the removal of a 2-carbon unit and hydroxylation at C-17

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Estradiol is synthesized from testosterone by the removal of C-19 and formation of the aromatic A ring

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29. All steroid hormones are derived from cholesterol

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30. A hugh array of biomolecules, all called isoprenoids are synthesized using activated isoprenes

These include many pigments (carotenoids, phytol chain of chlorophylls), fragrant principles, vitamines (A, D, E, K), rubber, dolichols, quinones (ubiquinone, plastoquinone), juvenile hormones of insects.

Prenylation of proteins (attaching of geranylgeranyl and farnesyl groups) leads to membrane association.

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30. A hugh array of biomolecules, all called isoprenoids are synthesized using activated isoprenes

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Some plant pigments are isoprenoids

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Some fragrant molecules are isoprenoids (called terpenes)

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Natural rubber is cis-polyisoprene

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Isoprenoid tails function to anchor proteins to membranes

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Charles BaudelaireCorrespondances

“Perfumes, colors and sounds echo

one another.”

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Summary

Fatty acid biosynthesis takes a different pathway from the reverse of its degradation and takes place in different cellular compartments.

The aceytl-CoA units are transported out of mitochondrial matrix as citrate.

Acetyl-CoA carboxylase catalyzes the rate-limiting step of fatty acid synthesis and is highly regulated by allosteric and covalent modifications.

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Palmitate, the usual final product of fatty acid synthesis, can be further elongated and desaturated in sER.

Eicosanoids are derived from arachidonate by the action of cyclooxygenases and peroxidases.

Phosphatidic acid (diacylglycerol 3-phosphate) is the common precursor of both triacylglycerol and glycerophospholipids.

Glycerophospholipids are made using two alternative strategies of CDP modification.

The backbone of sphingolipids are made from palmitoyl-CoA and Ser.

Summary

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Radioisotope tracer experiments revealed that all the 27 carbons of cholesterol are from acetyl-CoA.

The biosynthesis of cholesterol takes a long pathway, with the reaction catalyzed by HMG-CoA reductase being the rate-limiting step for de novo synthesis of cholesterol.

Activated isoprene untis, mevalonate, squalene were found to be important intermediates of cholesterol biosynthesis.

Summary

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The lipids are transported as lipoprotein particles (including chylomicrons, VLDL, LDL, and HDL).

The de novo biosynthesis of cholesterol is regulated to complement the dietary uptake.

All streroid hormones are derived from choleterol.

A huge arrays of isoprenoids are made using activated isoprene units.

Summary

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Chapter 14