Phospholipids (17)

Under which circumstances is TG synthesis favoured?

After a fatty meal

Under which circumstances is PL synthesis favoured?

1. When cells are dividing

2. To maintain membrane rafts balance

3. To provide signaling molecules (stress, IP₃, DAG)

What are membrane rafts?

Microdomains of the cell membrane, specifically the thick and stiff ones

What makes RAFT domains thick and stiff?

It has more sphingomyelin/less PL and more cholesterol

Describe non-RAFT domains

Thin and fluid sections of the cell membrane (more PL/less sphingomyelin and less cholesterol)

What differenciates a sphingomyelin from a PL?

Sphingosine backbone instead of a glycerol one

Discuss further difference between PL and SGM

1. 2 FA vs 1 FA

2. Amide group on the FA of SGM

Discuss the structure of glycolipids

Same sphingosine backbone

Discuss the structure of cholesterol (2)

• Amphipatic

• Very rigid from the aromatic rings

How is there many kinds of PLs?

By changing the head group/group attached to the phosphate on C3

Name the 3 enzymes that maintain the in/out asymetry of the membrane

Flippase, floppase and scramblase

What is the last function of membrane lipids?

Signaling : Phosphatidylinositol (PI) → PIP3→ PIP2 → IP3

What are the glycerophospholipids that have the same synthesis mechanism?

PI, PG and cardiolipin

Step 1 of GP synthesis

Activation (addition of nt) of a phosphatidic acid (PA) with the energy from inorganic pyrophosphatase

What is the equation for reaction #1?

PA + CTP → CDP-DAG + PPi

Step 2 of GP synthesis

Addition of inositol OR G3P:

1. Insitol = PI

2. G3P = PG

3. G3P + cardiolipin synthase = Cardiolipin

What are the GP that are synthesized through the Kennedy Pathway?

PE and PC

What differenciates PE and PC?

The R group:

• -H in PE

• -CH3 in PC

Step 1 of the Kennedy Pathway

Prime the head group w ATP = transfer of a phosphate group

Step 2 of the Kennedy Pathway

Activate w CTP

Step 3 of the Kennedy Pathway

Add diacylglycerol/DG

By what pathway can you change PE into PC?

The one-carbon pathway

Steps of the one-carbon pathway (2)

1. Methionine + ATP → SALM (adenosyl methionine)

2. Add 3 groups to PE by using PEMT

Which function is highly dependent on abundant PC in the lvier?

Bile synthesis : an imbalance can lead to gallstones

What symptom is observed in case of a PEMT deficiency and why?

Fatty liver : accumulation of TGs bc PC is necessary for VLDL packaging

What is the enzyme needed to convert PE → PS?

PES transferase

What is the enzyme needed to convert PS → PE?

PS decarboxylase

Step #1 of SL synthesis

Activated acyl group + Serine backbone

Step #2 of SL synthesis

a) Add phosphocholine head group = Sphyngomyelin

b) Add a glucose head group = glycosphingolipid/GSL

Where are phospholipases located?

Plasma membrane

What does cleaving a PL at different carbons do? (3)

1. Generate signaling molecules (PLC : -O at C1)

2. Convert PLs

3. Modulate shape of membrane

How is Nieman-Pick Typa A/B disease caused?

PL deficiency

Through which cycle are PLs cleaved?

Lands’ cycle

What are the 2 interchangeable molecules of the Lands’ cycle?

PLs and lypophospholipids/LPLs

How is Lands’ cycle related to the shape of the membrane?

LPLs have a conical shape which introduce a curvature in the membrane