Lipid FUNCTION

Phospholipid

lipids that form the structural basis of all cell membranes, including membrane of organelles within the cell

• Phosphate-containing lipids:

• SFA in position 1 and USFA in position 2

Phospholipid key points ->

Amphipathic

Anchoring proteins

Physiologically active

Biological roles of phospholipids

•  Attract water molecules

  • form the foundational structure of lipid bilayers that comprise cell membranes

• Lipoprotein Stabilization:

• Physiologically Active & Signaling Roles

Phospholipid’s  dynamic role as a signaling

Done through particiularlly phosphatidylinositol

• LOC: cytosolic side of cell membranes

• When ex cellular stimuli offcurs, its response is to create distinct phosphoinositides

Effect of Phosphoinositides

Effector Protein Recruitment: 

attract regulatory ("effector") proteins that manage crucial membrane activities 

• (membrane fusion, ion channel regulation, endocytosis)

Key Signaling Pathways Involving Phosphoinositides

1. The PIP₂ Pathway:

2. The PIP₃ & Insulin Signaling Pathway:

The PIP₂ Pathway:

1. PIP2 + protein kinase C & phospholipase C (integral proteins)

   1. *NOTE Phospholipase C Action

Phospholipase C Action

Hydrolyzes PIP2 → IP3 & DAG 

• both serve as vital second messengers in cell signaling

Sphingolipids

participate in cell signaling & providing mechanical stability, protective barriers, and organizational integrity

The PIP₃ & Insulin Signaling Pathway

1. Insulin binds + receptor = PI3K phosphorylates PIP2->PIP3

2. PIP3 recruits protein kinases to cell (ie Protein Kinase B/Akt)

   1. phosphorylate many enzymes regulating carbohydrate, protein, & lipid metabolism

Lipoprotein Stabilization

a monolayer on the surface of bloodborne lipoprotein particles, stabilizing them in aqueous bodily fluids (blood plasma)

Phospholipids Structure visual

Phospholipids Structure FA Arrangement

named according to their specific head group (as phosphatidyl derivatives of alcohols) rather than their fatty acids.

Phospholipids Structure Naming

 most abundant phospholipid in mammalian tissues, making up roughly half of the phospholipids in cell membranes.

• Sourced from egg yolks

Phospholipids specialized functions

• Phosphatidylserine

• Phosphatidylinositol

Phosphatidylserine

acts as a signal that attracts phagocytes during cellular degradation.

• Plays a role in apoptosis

Phosphatidylinositol

Involved in several crucial intracellular signaling & cellular function

Diphosphatidylglycerol/Cardiolipin

• A phospholipid in tissues

contains three glycerol molecules and four fatty acids.

• anchors protein complexes I, III, and IV of the ETC & facilitates ATP productio

Plasmalogen

phospholipid in heart (choline 40%) + brain (ethanolamine 30%)

Sterols

Four-ring steroid nucleus and at least one hydroxyl group

Has 3 categories→

1. Cholesterol

2. Bile Acids

3. Phytosterols

Cholesterol Purpose

Precursor for many steroids

• constituent of plasma membranes along with phospholipids due to its amphipathic nature

Cholesterol Regulation (in excess)

esterifying “excess” cholesterol with a FA and storing the cholesterol esters in vesicles within the cytosol

Cholesterol Regulation (in need)

cholesterol esters are hydrolyzed and free cholesterol is transported back to the membrane.

Bile Acids

critical components of bile that act as detergents in the small intestine to emulsify dietary lipids for digestion and absorption. 

• Liver synthesis

• Reabsorption into enterohepatic circ, return to liver

Phytosterols

Contained in plant cell membranes

• Stanols

Stanols

help lower blood low-density lipoprotein (LDL) or "bad" cholestero

Sphingolipids

participate in cell signaling & providing mechanical stability, protective barriers, and organizational integrity

Subtypes →

1. Sphingomyelin

2. Cerebrosides

3. Gangliosides

Sphingomyelin

phosphocholine + ceramide = lipid raft

Important for  nervous system function (abundant in myelin sheath)

Purpose → regulate cell signaling and protein sorting

Cerebrosides

serve a protective role, acting as an insulator and facilitator in the proper conduction of nervous impulses (nerve impulse conduction)

Subtypes →

1. Galactocerebrosides (w/ -gal)

   1. Myelin sheath 

2. Glucocerebrosides (w/ -glu)

   1. spleen and RBCs

Galactocerebrosides (w/ -gal)

ceramide backbone + galactose

LOC: Myelin sheath

Purpose → Provides structural stability and insulation to myelin, preventing ion leakage and enabling rapid nerve signal transmission

Glucocerebrosides (w/ -glu)

Ceramide backbone + Glucose

LOC:spleen and RBCs

Purpose → Acts as the building block (metabolic precursor) for complex glycolipids and maintains cell membrane integrity

Gangliosides

markers in cellular recognition and as receptors for certain hormones and toxins, including the cholera toxin

• Similar to cerebrosides BUT w/multi. S.u.’s linked to ceramide