Session 1 - The Membrane Bilayer Flashcards
Where are phospholipids synthesised?
Endoplasmic reticulum
Which 4 types of molecules can be employed as head groups on phospholipids?
Choline, amines, amino acids and sugars
Which 2 fatty acid side chain lengths are most common in naturally occurring phospholipids?
C16 and C18
Double bonds in fatty acid side chains of naturally occurring phospholipids are in which conformation?
Cis
What effect does the introduction of double bonds into phospholipids fatty acid chains have?
Decreases the ability of the phospholipids to form two-dimensional crystals
What is the least thermodynamically favourable mode of phospholipid mobility in a membrane?
Flip-flop
Which modes of mobility are permitted in membrane lipids?
Rotational movement, vibrational movement, lateral diffusion and flip-flop movement
How does cholesterol bond to phospholipid molecules?
Cholesterol hydroxyl groups form hydrogen bonds with the double bonded oxygen atoms in the ester bonds of the phospholipid molecules
What is the typical ratio of cholesterol to phospholipid molecules in a membrane?
1:1 ratio
What effect does cholesterol have on membrane fluidity and why?
Reduces membrane fluidity because it reduces the phospholipid fatty acid side chain’s mobility
How can integral transmembrane proteins move within a membrane?
Via conformational changes, fast axial rotation or fast lateral diffusion
How can peripheral membrane proteins be bound to the surface of a membrane?
Via electrostatic interactions; hydrogen bonding; or disulphide bonding
How can peripheral membrane proteins be removed from a membrane?
By modifying pH or modifying ionic strength
How can integral membrane proteins be removed from a membrane?
Using solvent extraction or detergent extraction
Integral membrane proteins interact extensively with which regions of a membrane bilayer?
Hydrophobic regions
The membrane spanning domains of membrane proteins are usually formed by which secondary structure?
Alpha helix
Where are mitochondrial membrane proteins synthesised?
In the cytoplasm
Where does membrane protein biosynthesis begin?
In the cytoplasm
What type of it all sequence do lysosomal membrane proteins have?
Hydrophobic
How is the arrest of membrane protein biosynthesis mediated?
By the binding of signal recognition binding proteins
Which part of the ER recognises the SRP on a protein?
The docking protein
How are membrane protein-synthesising ribosomes anchored to the ER?
Using ribophoryns
How is passage of membrane proteins through the ER arrested?
Using a stop transfer sequence on the protein
What usually follows the stop transfer sequence on the C-terminal side of a protein?
Two basic residues
How is a core carbohydrate group transferred to a newly synthesised membrane protein?
From a dolichol phosphate carrier lipid
What catalyses formation of disulphide bonds in post-translational processing of proteins?
Protein disulphide isomerase
Where are disulphide bonds formed in post-translational modification?
In the ER
Where do the final post-translational carbohydrate modifications of proteins occur?
In the trans-Golgi
What is required to target newly synthesised membrane proteins to lysosomes?
Glycosylation
In phospholipids, which atoms on the glycerol backbone are fatty acid side chains attached to?
C1 and C2
