Membrane Lipids Flashcards
Recommended Readings: CH. 9 Lipid Classification: pp. 245-254, particularly 249-253 Lipid Bilayers: pp. 259-261 (5th) Membrane Proteins: pp. 262-268 Membrane Structure and Assembly: pp. 269-271, 274-276 Practice Problems Ch 9 Q's 3, 4, 6-8, 17, 18, 21, 22, 29 (5th)
Describe the structural features common to all membrane lipids.
Amphipathic
- Hydrophilic end = Polar Head Group
- Hydrophobic end = Fatty acid tails
Typically carry a Net Neutral or Negative charge in the polar portion of the lipid
Five Membrane Lipid Types:
(1) glycerophospholipid
(2) sphingolipid,
(3) galactolipid,
(4) tetraether lipid,
(5) sterols,
glycerophospholipid: Amphiphilic Lipiid in which two Fatty Acyl Groups are attached to a glycerol-3-phosphate whose phosphate group is linked to a polar group
- aka Phosphoglyceride
- Built on Glycerol-3-phosphate backbone (central core)
- Glycerol is prochiral not chiral but Glycerol-3-phosphate is
- Usually Unsaturated
- Fatty acids are attached via ester linkages to carbons 1 (usually saturated) and 2 (unsaturated)
Polar Substituent is attached to the Phosphate
- Alcohol attached via phosphodiester
- Determines the “type” of Glycerophospholipid
Sphingolipid: Five Membrane Lipid Types:
(1) glycerophospholipid
(2) sphingolipid,
(3) galactolipid,
(4) tetraether lipid,
(5) sterols,
Sphingolipid: A derivative of the C18 amino alcohol sphingosine (non-glycerol // backbone)
- Sphingosine synthesized from serine and palmitate
- include ceramides, cerebrosides and gangliosides
- Those with phosphate head groups are called sphingophospholipids
Structure:
- Single Fatty acyl Chain Attached via amide bond
- Polar head group attached to C1 is variable and determines class
- sphingosine (non-glycerol) backbone (synthesized from serine and palmitate)
- Contains a polar and non-polar region
Sphingomyelin: phosphocholine or phosphoethanolamine
Cerebrosides: monosaccharide (glucose or galactose)
Globosides: neutral oligosaccharide strucutre (2+ sugars)
Gangliosides: oligosaccharides including at least one Sialic Acid
Galactolipid
Five Membrane Lipid Types:
(1) glycerophospholipid
(2) sphingolipid,
(3) galactolipid,
(4) tetraether lipid,
(5) sterols,
Galactolipids and sulfolipids do not require phosphate (advantageous as limited supply)
-Sulfonates may carry Neg charges like phosphate
Galactolipids:
- 1 or 2 galactose units at C2, acyl chains at C1, C2
- Acyl Chains derived from 18:2delta ^9,12 (linoleic acid)
tetraether lipid
Five Membrane Lipid Types:
(1) glycerophospholipid
(2) sphingolipid,
(3) galactolipid,
(4) tetraether lipid,
(5) sterols,
Archae are extremophiles
Tetraether lipids: 4 ether bonds
Special Lipid Structures:
- Phospholipids
- Ether-linked (ether instead of ester, harder to break with hydrolysis in heat/acid)
- Branched isoprenoid chains
Sterols
Five Membrane Lipid Types:
(1) glycerophospholipid
(2) sphingolipid,
(3) galactolipid,
(4) tetraether lipid,
(5) sterols,
Sterols:
- Rigid membrane lipids with fused ring systems
- Cholesterol is common
- Length equivalent to a 16:0 fatty acyl group
Define the following lipid terms:
- glycolipid,
- phospholipid,
- sulfolipid.
pending
Identify and name the common glycerophospholipids based on their polar headgroup.
image
Phosphatidytinositol-4,5-bisphosphate
Draw the structure of the common glycerophospholipids
Phospholipases
Define the specificities for phospholipases A1, A2, C, and D and name/describe the products generated by their activity.
Phospholipases degrade glycerophospholipids
Type-A Phospholipases (hydrolase) cleaves acyl groups (yielding fatty acid + alcohol)
- A1 - from C1
- A2 from C2
Type C and D cleave the polar head group on either side of the phosphate group at C-3
Ceramide:
Define the term ceramide and explain the structural role of ceramides in sphingolipids.
Ceramide:
Sphingosine + Fatty Acid via Amide linkage
Ceramides are bioactive sphingolipids that support the structure of the plasma membrane and mediate numerous cell-signaling events in eukaryotic cells.
Describe the composition of cerebrosides, globosides and gangliosides.
Sphingomyelin: phosphocholine or phosphoethanolamine // Net neutral
Cerebrosides: monosaccharide (glucose or galactose) // Net neutral
Globosides: neutral oligosaccharide strucutre (2+ sugars)// No charge aspect Ooligosaccharide)
Gangliosides: oligosaccharides including at least one Sialic Acid // Net neutral or NEG
Describe and identify the distinguishing features of the structures of sphingomyelins, glycosphingolipids and gangliosides.
image
Describe the generic structure of a galactolipid, and the advantage to plants of using sulfogalactolipids in their membranes rather than glycerophospholipids.
Galactolipids and sulfolipids do not require phosphate (advantageous as limited supply)
-Sulfonates may carry Neg charges like phosphate
Galactolipids:
- 1 or 2 galactose units at C2, acyl chains at C1, C2
- Acyl Chains derived from 18:2delta ^9,12 (linoleic acid)
Describe the general features of archael ether lipids and explain the advantages of ether linkages in archael membrane lipids.
Archae are extremophiles
Tetraether lipids: 4 ether bonds
Special Lipid Structures:
- Phospholipids
- Ether-linked (ether instead of ester, harder to break with hydrolysis in heat/acid)
- Branched isoprenoid chains
Outline how phosphatidylinositol-4,5-bisphosphate can form two signalling molecules and the role that each molecule can play.
Two signalling molecules, diacyl glycerol (DAG) and inositol 1,4,5-trisphosphate (Ins[1,4,5]P3), are generated from PtdIns[4,5]P2 by PtdIns-PLC catalysis
Cleavage by phospholipase C to form two allosteric effectors
- DAG
- IP3
DAG is an important signalling molecule activating the downstream effector, protein kinase C (PKC)
