Flashcards in Lecture 35: Eicosanoids Deck (63)
Other than being used to form lipid bilayers, what else are 5 important functions of lipids?
1. Module activities of soluble and membrane-bound proteins
2. Tether GPI-anchored membrane proteins (phosphatidylinositol)
3. Act as molecular signals
4. Have derivatives that act as intracellular second messengers in transduction pathways
5. Potent short-lived hormone-like molecules = eicosanoids!
What is an example of a lipid functioning as a molecular signal?
Ether-linked glycerophospholipid platelet activating
What is an example of a lipid having derivatives that act as intracellular second messengers in transduction pathways?
Phosphatidylinositol (PIP2) breaking into inositol 1,4,5-triphosphate and diacylglycerol, which
then go on to regulate other enzymes
How is an eicosanoid formed?
1. Physical damage, hormonal signal, or neuronal signal
2. PLP A2 cleaves a polyunsaturated FA on a glycerophospholipid
3. Polyunsaturated FA either enter cyclic (cyclooxygenase) or linear (lipoxygenase) pathway depending on what enzyme acts on it
4. Eicosanoid is produced
List 6 types of eicosanoids.
What is the nomenclature to name eicosanoids?
1. n series leukotrienes (LT)
2. n-2 series prostaglandins (PG)
3. n-2 series thromboxanes (TX)
n = number of unsaturated bonds in the FA
What does the ω-system of naming FAs mean? Note?
Number after omega = number of Cs before encountering a double bond starting from the omega end of the FA (aka the terminal methyl group)
Note: count the first C included in the double bond
Can mammals desaturate FAs?
Not very good at this, especially close to the omega end
What organisms are good at desaturating FAs close to the ω-end? What enzymes do they use?
Plants using plant acyl desaturases in chloroplasts
Can mammals synthesize ω-3 FAs?
NO, we can only get them from the diet
In what food do we find ω-3 FAs?
Cold water fish and flax seed
What are the 3 ω-3 FAs?
1. alpha-linoleic acid
2. Eicosapentaenoic acid
3. Docosahexaenoic acid
Describe the synthesis of unsaturated FAs starting with palmitic acid. Which 2 are essential for us?
1. Palmitic acid - 16:0
2. Stearate - 18:0
3. Oleate - 18:1
4. Linoleate - 18:2 (ESSENTIAL)
5a. γ-linoleate - 18:3
5b. alpha-linoleate (ESSENTIAL)
6. Eicosatrienoate - 20:3
7. Arachidonic acid - 20:4
What is a health benefit of eating ω-3 FAs?
Reduced risk of heart attack
Glycerophospholipid cleavage: phospholipase D: cleavage site? products?
Cleavage site = bond between polar head group and P
Products = phosphatidic acid + polar head group
Glycerophospholipid cleavage: phospholipase C: cleavage site? products?
Cleavage site = bond between P and O attached to C3
Products = head group-P-O2 + DAG
Glycerophospholipid cleavage: phospholipase A1: cleavage site? products?
Cleavage site = FA-O bond at C1
Products = FA + lysophospholipid
Which glycerophospholipids are resistant to phospholipase A1? Why?
Ether-linked glycerophospholipids: plasmalogens and platelet activating factor because PLPAs can only cleave ester bonds
What are 2 ether-linked glycerophospholipids? What is the difference with normal glycerophospholipids?
2. Platelet-activating factor
They have an ether-linked alkane/alkene chain instead of an FA at position 1
What are the 2 possible head groups for plasmalogens?
Where is the double in plasmalogens? What do we call these molecules?
Between C1 and C2 of the alkene chain
Describe the composition of the platelet-activating factor. What does the position 2 portion of it allows it do to?
1. Ether linked alkane chain at position 1
2. Acetyl ester at position 2: small group allowing the molecule to circulate and be soluble in blood
3. Phosphocholine head group at position 3
Glycerophospholipid cleavage: phospholipase A2: cleavage site? products?
Cleavage site = FA-O bond at C2
Products = FA + lysophospholipid
What enzyme is the rate-limiting step of eicosanoid synthesis?
PLP A2 activation
What hormones can inhibit PLP A2?
Describe the mechanism used in the cyclic pathway of eicosanoid synthesis with an ω-6 FA? Include locations
Step 1: SER: |protaglandin synthase=cyclooxygenase + hydroxiperoxide|: arachidonic acid => Prostaglandin H2
Step 2: Prostaglandin H2 =>
- Prostacyclin synthase: Prostacyclins (PGI2)
- Thromboxane synthase: Thromboxanes (TXA2)
Why does aspirin have an anti-clotting effect? What is the side product?
INHIBITS cyclooxygenase (COX1 and 2 equally) by IRREVERSIBLE binding Ser at active site and acetylating it (side product: salicylate)
How do NSAIDs other than aspirin work?
INHIBIT cyclooxygenase (COX1 and 2 equally) by REVERSIBLE binding Ser at active site
What are the 3 isoforms of cyclooxygenase?