Lecture 2 - Structures Of Membrane Lipids Flashcards
What are phosphatidylcholine?
Class of phospholipids that incorporate choline as a head group
What is a major component of phosphatidylcholine?
Biological membrane
What are most phospholipids ?
Phosphoglycerides
What are most membrane Lipids?
Phospholipids
Phosphoglycerides
Two fatty acids, phosphoric acid and glycerol
Why is glycerol a convenient component to stick things too ?
Hydroxyl groups are easy to make connections too - condensation reaction with a fatty acid
Which bit of the molecule can vary?
Modify head group Fatty acid chains —> influences the thickness of bilayer Introduce double bones (desaturate it)- makes it less flexible but makes the membrane more fluid
What remains the same in phosphoglycerides?
Phosphate and glycerol
What does phosphatidylinostil do?
Linking proteins to membrane Role in cell signalling
Cardiolipin
Lipid with properties found in the membranes generating electrochemical potential 4 acyl chains and tends to form nonlamellar structures Unusual —> double phosphoglycerides Creates a Lipid with 4 tails Special Role in inner mitochondrial membrane - help the association of specific proteins
Sphingolipids
Fatty acid derivatives of sphingosine Occur chiefly in the cell membrane of the brain and nervous tissue Range of different head groups
Sphingomyelin
Derivative of sphingosine and choline
What is a way to classify Lipids?
Glycolipids
What are sugars ?
Not charged - but very Polar and water soluble
Cholesterol
Influenced the mechanical property of the membrane - makes it more stretchy, flexible and fluid over a wide range of temperatures Nearly all hydrophobic Largely absent from plant cells
What are problems associated with cholesterol?
Complicated structures with rings - cannot pack as well Only hydrophilic and polar group: OH group
What is cholesterol very closely related in structure and biosynthesis pathway with?
Testosterone and Oestrogen
Mammalian plasma membrane (human erythrocytes)
Phosphoglycerides (PC, PE, PS) Sphingomyelin Glycolipid. Cholesterol (25%) No cardiolipin No PG
Mitochondrial inner membrane (beef heart)
Phosphoglyxeride (PC, PE) Cardiolipin Not much cholesterol No glycolipids No sphingomyelin
Bacterial plasma membrane (E.coli)
Phospgoglyceride (PE, PG) Cardiolipin (12%) No cholesterol No sphingomyelin No glycolipids
Lipid anchored proteins
Located outside the lipid bilayer, on either the extracellular or cytoplasmic surface, but are convaently linked to a lipid molecule that is situated within layer
Peripheral membrane proteins
Attachment to membrane surface - non covalent associations Do not penetrate he hydrophobic tails
What does lipid bilayer give to the membrane?
Fluidity and elasticity
How does Singer and Nicholson deserve the cell membrane?
2D liquid that restricts the lateral diffusion of membrane components
What are the stable confirmation of the polypeptide backbone?
Alpha helix and beta sheets
Alpha helical structure
The backbone of the polypeptide chain is all hidden in the rod-like structure
Integral membrane proteins
Faced on hydrophobic alpha helices Hydrophilic domain stick out on the surface of membrane Have one membrane-spanning segment whereas others are multi-spanning
What does genome sequencing studies suggest?
Integral proteins constitute 20-30% of all encoded proteins
Transmembrane protein
They pass entirely through the lipid bilayer and thus have domains that protrude from both the extracellular and cytoplasmic side of membrane
