UNIT 6. Synthesis of Fatty Acids, Complex Lipids, and Eicosanoids

True

(T/F) Fatty Acid Biosynthesis and Degradation Pathways are Different

four

There are ____________major differences between fatty acid breakdown and biosynthesis

• Intermediates in synthesis are linked to -SH groups of acyl carrier proteins (as compared to -SH groups of CoA in oxidation)

• Synthesis in cytosol; breakdown in mitochondria

• Enzymes of synthesis are one polypeptide, the fatty acid synthase

• Biosynthesis uses NADPH/NADP+ while Fatty acid breakdown uses NADH/NAD+

What are the major differences between FA biosynthesis vs FA breakdown

Acetate Units

Formation of Malonyl-CoA Activates ________for Fatty Acid Synthesis

two carbon units

[The design strategy for fatty acid synthesis]

1) Fatty acid chains are constructed by the addition of___________derived from acetyl-CoA

carboxylation with CO2

[The design strategy for fatty acid synthesis]

2) The acetate units are activated by ______________to form malonyl-CoA (at the expense of ATP)

decarboxylation of malonyl-CoA

[The design strategy for fatty acid synthesis]

3) The addition of two-carbon units to the growing chain is driven by __________________________________

16 carbons in length (palmitic acid)

[The design strategy for fatty acid synthesis]

The elongation reactions are repeated until the growing chain reaches _________________________

double bonds and additional carbon

[The design strategy for fatty acid synthesis]

Other enzymes then add _____________ & ___________________ units to the chain

Cytosolic Acetyl-CoA and NADPH

Cells Provide __________________ & ________________ for Fatty Acid Synthesis

Acetyl-CoA Carboxylase

Carboxylation of Acetyl-CoA to Form Malonyl-CoA is Catalyzed by ______________________

Acetyl-CoA Carboxylase (ACC) enzyme

The __________________ commits acetate to fatty acid synthesis

irreversible & committed step

Carboxylation of acetyl-CoA to form malonyl-CoA is the ______________ & __________ in fatty acid biosynthesis

bicarbonate and ATP (AND biotin)

ACC uses ______________and _________ & _________

• biotin carboxyl carrier protein

• biotin carboxylase

• carboxyltransferase

What are the three E.coli enzyme subunits? (3)

• Animal enzyme is one polypeptide with all three functions (subunits)

1. Bicarbonate ; carbonyl phosphate intermediate.

2. acetyl-CoA carbanion; N- carboxybiotin

[Formation of Malonyl-CoA]

1. carboxylation of biotin

   • __________is activated for carboxylation reactions by formation of N-carboxybiotin. ATP drives the reaction forward, with transient formation of a __________________

2. transcarboxylation reaction

   • In a typical biotin-dependent reaction, nucleophilic attack by the ________________ on the carboxyl carbon of ___________________– a transcarboxylation – yields the carboxylated product.

biotin ring ; carbonyl phosphate

In the ACC reaction, the ______________ acquires carboxyl groups from _______________ on the biotin carboxylase subunit.

inactive protomers; biotin carboxyl carrier moiety, biotin carboxylase, and carboxyl transferase

In animals, acetyl-CoA carboxylase (ACC) is a long, active filamentous polymer formed from_______________. Each of these protomers contains the __________________ (3)

regulated; active polymeric; citrate activation and palmitoyl-CoA inhibition

As a committed step, ACC is carefully __________. Palmitoyl-CoA (product) favors monomers. Citrate favors the _____________ form. Phosphorylation of ACC modulates________________ &______________

phosphorylation state; 8 to 10 sites

The regulatory effects of citrate and palmitoyl-CoA are dependent on the ______________ of acetyl-CoA carboxylase. The animal enzyme is phosphorylated at ___-____ on each enzyme subunit

• citrate; low [citrate]

• high Ki for palmitoyl-CoA ; high [palmitoyl-CoA]

• citrate; high [citrate]

• low Ki for palmitoyl-CoA ; low [palmitoyl-CoA]

• Unphosphorylated E has high affinity for __________ and is active at__________________

• Unphosphorylated E has ____________________and_________________ is required to inhibit

• Phosphorylated E has low affinity for _____________and ______________ is needed to activate

• Phosphorylated E has _____________and is inhibited at ______________

• low [citrate]; high levels of fatty acyl CoA

• high levels of citrate

The activity of acetyl-CoA carboxylase is modulated by phosphorylation. The dephospho-form of the enzyme is activated by ____________ and inhibited only by _________________.

In contrast, the phosphorylated enzyme is activated by__________

Acyl Carrier Proteins (ACP)

________________________________is the carrier of intermediates in fatty acid synthesis

false; its a large coa

(T/F) ACP In terms of function, is just a small “CoA”

coenzyme A and to acyl carrier protein ; sulfhydryl group

Fatty acids are conjugated both to _______________________through the __________________ of phosphopantetheine prosthetic groups.

fatty acyl synthase I (FAS I); 270-kD polypeptides

Fatty acid synthesis in mammals occurs on homodimeric________________. It consists of_______________which contain all the reaction centers required to produce a fatty acid

two multifunctional polypeptide chains; fatty acid synthase II (FAS II)

In yeast and fungi (lower eukaryotes), the activities of FAS are distributed on_______________________. In plants and bacteria, the enzymes of FAS are separate and independent, and this collection of enzymes is referred to as ___________________

true

(T/F) The individual steps of fatty acid synthesis are similar across all organisms.

mammalian pathway

The ________________ is a cycle of elongation that involves six enzyme activities

malonyl-CoA-acetyl-CoA-ACP transacylase (MAT)

Elongation (mammalian pathway) is initiated by transfer of the acyl moiety of acetyl-CoA to the acyl carrier protein by the__________________________. This enzyme also transfers the malonyl group of malonyl-CoA to ACP

ACP conjugates; β-ketoacylACP-synthase reaction

Acetyl and malonyl building blocks are introduced as __________________. Decarboxylation drives the ___________________ and results in the addition of two-carbon units to the growing chain.

acetyl group; ketoacyl synthase; malonyl group; C-C bond

[Mechanism for the Mammalian Ketoacyl Synthase]

An _______________ is transferred from CoA to MAT, then to the acyl carrier protein, and then to the _________________. Next a______________ is transferred to MAT and then to the acyl carrier protein. ____________ formation follows

closed barrel

Fungal FAS is a _____________.

a: ACP -KR-KS-PPT

B- AT -ER- DH- MPT

The arrangement of the functional domains along the FAS α and β polypeptides is

a: _______-________-_______-_____

B: ________-________-________-________

asymmetric X shaped

Mammalian FAS is an _______________ structure.

a: KS-MAT-DH-ER-KR-ACP-TE

The arrangement of the functional domains along the FAS polypeptide is

a-______-______-______—-_____-_____-_____-______

in mitochondria and ER

C16 Fatty Acids May Undergo Elongation and Unsaturation but where doe it happen? (2)

• O2 -independent process

• O2 -dependent process

[Introduction of cis double bonds]

Prokaryotes use an_____________

Eukaryotes use an _______________

functional group (the thioester);

middle of the chain; O2

E.coli add double bonds while the site of attack is still near a _______________________. Eukaryotes add double bond to _______________ - and need the power of ______to do it

1. Thiolase reaction (AC→ B-KetoaCOA)

2. L-B-hydroxyacyl-CoA dehydrogenase (B-KetoaCOA → L-B-hydroxyacyl-CoA)

3. Enoyl-CoA hydratase (L-B-hydroxyacyl-CoA→a,B trans-enoyl CoA)

4. no enzyme (a,B trans-enoyl CoA→ 2 A-CoA w/2 units)

4 steps in Elongation of fatty acids in mitochondria

true

(T/F) Double bonds are introduced into the growing fatty acid chain in E. coli by specific dehydrases.

• four rounds of chain elongation

• β-hydroxydecanoyl thioester dehydrase

• cis-vaccenoyl-ACP

[Double Bond Formation in Prokaryotes]

Palmitoleoyl-ACP is synthesized by a sequence of reactions involving __________________,, followed by double bound insertion by ________________ and three additional elongation steps. Another elongation cycle produces cisvaccenic acid, as _____________

stearoyl-CoA desaturase ; cytochrome b5 and cytochrome b5 reductase; Two electrons

[Unsaturation Reactions in eukatyotes]

The conversion of stearoyl-CoA to oleoyl-CoA in eukaryotes is catalyzed by ____________________in a reaction sequence that also involves _____________& ______________________. ____________________ are passed from NADH through the chain of reactions as shown, and two electrons are derived from the fatty acyl substrate

linoleic acid;

Arachidonic acid is synthesized from ________________ in eukaryotes.

_________& _________ – Essential Fatty Acids with Many Functions

• arachidonic acid ; ω6

• eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); ω3

• Linoleic acid is the precursor of___________and both these are termed___________ fatty acids

• Linolenic acid is the precursor of _________ &___________ and these three are termed ___ fatty acids

ω3

__________ fatty acids are cardioprotective, antiinflammatory, and anticarcinogenic

ω6

____________fatty acids are precursors of prostaglandins, thromboxanes, and leukotrienes

allosteric modifiers, phosphorylation and dephosphorylation cycles and hormones

Regulatory control of fatty acid metabolism is an interplay of (4)_________________________________

Malonyl-CoA

[Regulation of Fatty Acid Synthesis]

___________ blocks the carnitine acyltransferase and thus inhibits beta-oxidation

Citrate

[Regulation of Fatty Acid Synthesis]

______________activates acetyl-CoA carboxylase

Fatty acyl-CoAs

[Regulation of Fatty Acid Synthesis]

_____________ inhibit acetyl-CoA carboxylase

Hormones ; phosphorylation/dephosphorylation

[Regulation of Fatty Acid Synthesis]

___________regulate acetyl-CoA carboxylase (ACC) through________________/_________________

Glucagon

[Regulation of Fatty Acid Synthesis]

_________activates lipases/inhibits ACC

Insulin

___________inhibits lipases/activates ACC

• Glucagon will bind to receptors which will convert ATP to cAMP which will activate the protein kinase and dephosphorylate the ACC (to inactivate), and it will phosphorylate TAGs lipase (to activate)

• Insulin will bind to receptors which will release phosphodiesterase convert cAMP to AMP which will activate the protein kinase and phosphorylate the ACC (inactivate), and it will dephosphorylate TAGs lipase (to inactivate)

How does Hormonal Signals Regulate ACC and Fatty Acid Biosynthesis

Sphingolipids and triacylglycerols ;

_________&_____________only made in eukaryotes

75% of phospholipids

PE accounts for _____________in E.coli. No PC, PI, sphingolipids, cholesterol in E.coli but some bacteria do produce PC

Lipins

____________ are phosphatases essential for Triglyceride Synthesis and Other Functions.

phosphatidic acid phosphatases (PAPs) ; transmembrane domains; cytosol

Lipins are _____________________that are widely conserved in eukaryotes but they lack ______________ and are extensively phosphorylated and confined to the ____________until activated

PAP binding; Nem1p and Spo7p; diacylglycerols and triacylglycerols

Activation occurs upon _____________ to a complex of two ER/nuclear transmembrane proteins –__________& _________ – followed by dephosphorylation of PAP. The lipin-Nem1p-Spo7p complex dephosphorylates PA to form __________________________

• triacylglycerol biosynthesis

• maintenance of nuclear structure

• organization of the ER membrane

Lipins are critical for (3)_______________________

Phosphatidic acid

_________________ is the precursor for all other glycerolipids in eukaryotes

phosphatidic acid (PA);

Synthesis of glycerolipids in eukaryotes begins with the formation of_______________, which may be formed from acyldihydroxyacetone phosphate or acylglycerol intermediates

Diacylglycerol and CDP-diacylglycerol

________________ & ________________are the principal precursors of glycerolipids in eukaryotes.

acyltransferases

Triacylglycerols are formed primarily by the action of ______________on monoacylglycerol and diacylglycerol

• PI in one step

• PG in two steps

• Cardiolipin in three steps

CDP-diacylglycerol is used in eukaryotes to produce: (3)

DP-diacylglycerol

_______________________ is a precursor of phosphatidylinositol, phosphatidylglycerol, and cardiolipin in eukaryotes

Dihydroxyacetone Phosphate

________________________ is a Precursor to the Plasmalogens

ether linkage; Ketone reduction

Acylation of dihydroxyacetone phosphate, followed by an exchange reaction produces the _______. ________________ is followed by acylation

CDP-ethanolamine ; desaturase

[Dihydroxyacetone Phosphate is a Precursor to the Plasmalogens]

________________delivers the head group. A ___________produces the double bond in the alkyl chain

acetylation; acetylhydrolase

Platelet-activating factor is formed by _____________ of 1-alkyl2-lyso-phosphatidylcholine. Platelet-activating factor is degraded by the action of ______________

Sphingolipid

___________Biosynthesis Begins with Condensation of Serine and Palmitoyl-CoA

serine and palmitoyl-CoA

[Sphingolipid Biosynthesis]

Initial reaction is a condensation of ___ & _________

pyridoxal phosphate (PLP)

[Sphingolipid Biosynthesis]

3-ketosphinganine synthase requires _______________as a coenzyme

Ketone

[Sphingolipid Biosynthesis]

________is reduced with help of NADPH

Acylation

[Sphingolipid Biosynthesis]

_____________is followed by double bond formation

ceramide

[Sphingolipid Biosynthesis]

Resulting __________is precursor for other sphingolipids

3-ketosphinganine synthase;

PLP-dependent condensation;

Reduction of the keto group

Biosynthesis of sphingolipids in animals begins with the____________________ reaction: a __________________ of palmitoyl-CoA and serine.___________________ ensues, catalyzed by 3-ketosphinganine reductase.

Eicosanoids

________________(i.e., “20-carbon” molecules) are ubiquitous breakdown products of phospholipids

arachidonic acid

Under certain stimuli, cells activate the breakdown of selected lipids to release _____________, the precursor of the eicosanoids

• Prostaglandins

• Thromboxanes

• Leukotrienes

• Other hydroxyeicosanoic acids

Eicosanoids are local hormones, including: (4)

Prostaglandins

[Eicosanoids Synthesis]

_______________are formed from arachidonate by oxidation and cyclization

prostaglandin endoperoxide H synthase (PGHS); cycloxygenase (COX)

[Eicosanoids Synthesis]

Biosynthesis is initiated by an enzyme from the endoplasmic reticulum,________________________________. Also known as _________________

• Cyclooxygenase (COX)

• glutathione-dependent Peroxidase (POX)

[Eicosanoids Synthesis]

PGHS enzyme has two different activities: (2)

phospholipids (PL)

[Eicosanoids Synthesis]

Arachidonic acid, derived from breakdown of _____________, is the precursor of prostaglandins, thromboxanes, and leukotrienes

abstraction ; rearrangement; C-15

[Prostaglandin endoperoxide H synthase]

The mechanism of the reaction begins with hydrogen atom ____________by a tyrosine radical on the enzyme, followed by ________________ to cyclize and incorporate two oxygen molecules.

Reduction of the peroxide at _______ completes the reaction.

COX

___________ is the site of action of aspirin and other analgesic agents.

Lipoxins,

___________ anti-inflammatory eicosanoids, are synthesized through the concerted actions of several lipoxygenases – including 5-LO, 12-LO, and 15-LO

transcellular biosynthesis

Lipoxins are products of____________________

eicosanoid products

Cell types lacking certain enzymes partner with cells having them to exchange intermediates and produce the needed ________________

Transcellular synthesis ; greater range of biological responses

_______________expands the number of active mediators synthesized in response to stimuli. The consequence is a ____________________________ than otherwise possible

arachidonic acid; nonsteroidal anti-inflammatory drugs (NSAIDs)

[Action of Nonsteroidal Anti-Inflammatory Drugs]

The first steps in conversion of______________ to prostaglandins are catalyzed by PGHS or COX. This enzyme is inhibited by the____________________

true

(T/F) Animals have two forms of COX: COX-1 and COX-2. The “COX-2 inhibitors” (e.g., Celebrex) bind to COX2 but not COX-1

• COX-1 has a bulkier isoleucine at position 523 which prevents binding of COX-2 inhibitors

• At the same position, COX-2 has valine, which accommodates the COX-2 inhibitors

differentiate cox I and Cox 2

Prostaglandins

________are potent mediators of inflammation

• Aspirin and bromoaspirin bind covalently to COX-1 and COX-2.

• Ibuprofen binds noncovalently to both.

• Celebrex and Deramaxx bind selectively to COX-2.

Where do different NSAIDS bind?

• Aspirin

• bromoaspirin

• Ibuprofen

• Celebrex

• Deramaxx

Arachidonic acid

_______________serves as a primary eicosanoid precursor if the cells which is an integral constituent of biological cell membrane, conferring it with fluidity and flexibility, especially in nervous system, skeletal muscle, and immune system

food or by desaturation and chain elongation; ion channels; brain and muscles

Arachidonic acid can be obtained from _________ or _____________________ of the plant-rich essential fatty acid, linoleic acid . It modulates the function of _________________, several receptors and enzymes, via activation as well as inhibition; its fundamental role in the proper function of the ______________

• endogenous anti-inflammatory molecules

• regulate components of both the innate and adaptive immune systems

Lipoxins

• are ____________________, pro-resolving molecules that play a vital role in reducing excessive tissue injury and chronic inflammation

• _____________________including neutrophils, macrophages, T-, and B-cells