Membrane Fluidity😊

Membrane Fluidity

Fluidity buffer: Maintains membrane fluidity in optimal range.

Lubricative property of lipid → Maintain fluidity of membrane → Allows mobility.

Phospholipids

ㅤ	Increased Fluidity	Decreased Fluidity
Effect on health	Good	Bad
Type of fatty acids	Unsaturated (Essential)	Saturated (Trans)
Examples	• Linoleic acid • α Linolenic acid • Arachidonic acid • Omega-3 fatty acids: Abundant in fish	• Stearic acid • Palmitic acid: (Abundant in junk food)

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ㅤ	SFA	MUFA	PUFA	PUFA
ㅤ	ㅤ	Omega -9	Omega -3	Omega -6
Example	• Lauric acid • Stearic acid • Palmitic acid	Oleic acid	α-linolenic acid Most essential fatty acid	Linoleic acid
Richest sources	Animal sources One plant source: Coconut oil	• Mustard oil • Groundnut • Olive • Avocado	Flax seed oil One animal source: Fish	Safflowers
Long/complex chain derivative & richest source	-	-	• Eicosapentaenoic acid • α-linolenic acid • Timnodonic acid • Cervonic acid ↳ Breast milk ↳ Fish ↳ Algal oil	• Linoleic acid • γ-linolenic acid • Arachidonic acid : ↳ Milk, egg Derivatives: ↳ Eicosanoids (Prostaglandins, Leukotrienes, Thromboxane A2)
ㅤ	Saturated Laura (Lauric acid) stearingil (stearic acid) coconut (coconut oil) palmil (Palmitic oil) kond idich	MUFA → 9 () Ola (Oleic) ayi MUST () goto GOA ()	3 → F → Flax → Fish	6 → FF → saFFlower

Lecithin-sphingomyelin (L/S) ratio:

Determinant of fetal lung maturity.
L/S ratio > 2 to 2.5 → Indicates mature fetal lungs.
Deficiency in pre-term baby

Hyaline Membrane Disease
Very low compliance.

Glycerophospholipids

Based on phosphatidic acid (PA) → Diacyl glycerol (DAG) + PO4

Key examples:

Surfactant Composition:

Primarily lipid (90%) and protein (10%).

Lipid	Other names	Function
M/c	DPPC • Dipalmitoylphosphatidylcholine / • Dipalmitoyl lecithin	= surfactant form
2nd m/c	PC • Phosphatidylcholine / • Lecithin	• general membrane phospholipid • → DAG + PO4 + choline • Most abundant in cell membranes

Surfactant Production:

Surfactant Production	Weeks of Gestation
Begins	20-24 weeks
Appears in amniotic fluid	28-30 weeks
Maturation	35-37 weeks

Surfactant action

Break force of attraction between water molecules lining alveoli

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Cardiolipin

(Diphosphatidyl glycerol)
Heart: mitochondria
Only antigenic PL
Inner mitochondrial membrane
Implicated in Barth, Syphilis, APLA

Barth syndrome

Cardiomegaly + myopathy

Cardiolipin involved

Mitochondrial disease

Bar → Alcohol → Dont drive car (Cardiolipin)

DCM → cardiomegaly
get beaten → Myopathy

In APLA

Cross reacts with Treponema pallidum:

false-positive VDRL/RPR test.

d/t Serum anti-CL antibody

Lupus anticoagulant

Anti-β2 Glycoprotein antibody
In vivo Procoagulant

Recurrent thrombosis

Invitro anticoagulant,

Prolonged PTT

not corrected by the addition of normal platelet-free plasma

Dilute Russell Viper Venom Time Test (DRVVT) derangement

due to autoactivation.

Other Major lipids

Types	Significance
Sphingomyelin	• Sphingophospholipids • Myelin sheath, brain white matter, lung surfactant • Lecithin: sphingomyelin ratio ↳ Marker for fetal lung maturity (↑ ratio = ↑ maturity).
Phosphatidylinositol (IP3)	• PA + Inositol • Endocrine cells Function • 2nd messenger in hormonal pathways (IP3 → DAG → Ca²⁺) • signal transduction.
Phosphatidylserine (Ps)	• PA + Serine • Inner surface of cell membrane in all cells Function • Eat me Signal (Apoptosis) Stained by Annexin V: ↳ Binds & forms complex with Ps

Carbohydrates

CLASSIFICATIONS

Glycoprotein: Attached to proteins.

Glycolipids: Attached to lipids.

SIGNIFICANCE

Glycolipids on RBC membrane:

Determine blood groups.

Blood Type	Red Blood Cell Antigens Displayed
A	Displays A antigen
B	Displays B antigen
AB	Displays A and B antigens
O	Lacks A and B antigens

Note

Membrane with highest protein:

Inner mitochondrial membrane.

In nerve cell membrane (myelin):

Lipid (80%)
Protein (20%)

Repair of damaged cell membrane is by resealing of lipid bilayer.

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