Lecture 14 - Membranes 1 Flashcards
Membranes form non-covalent or covalent assemblies?
non-covalent
What does it mean that the membrane is Asymmetrical?
The two faces of biological membranes are always different and face away from eachother.
Amphipathic refers to?
Definition: describing a molecule, such as a detergent, which has both hydrophobic and hydrophilic groups
the fact that membrane lipids contain a hydrophilic unit and hydrophilic unit
How can membrane lipids arrange
themselves in aqueous solution?
Two possibilities: Micelle or Lipid Bilayer (Bimolecular sheet)
When does a micelle form?
A micelle is formed when a variety of molecules
including soaps and detergents are added to water.
usually less than 20 nm in diameter
Why is the favored structure for most phospholipids and
glycolipids in aqueous media is a bimolecular sheet?
The reason is that the two fatty acyl chains of a
phospholipid or a glycolipid are too bulky to fit
into the interior of a micelle.
What are the Major driving forces for the assembly of lipid bilayers?
What is this process called?
self-assembly process
- Hydrophobic interaction (major)
- van der Waals attractive forces between hydrocarbon tails
• Electrostatic and hydrogen-bonding attractions between polar head groups and
water molecules
Consequences of hydrophobic interactions include? (properties)
- lipid bilayers have an inherent tendency to be extensive.
- lipid bilayers will tend to close on themselves so that there are no edges with exposed hydrocarbon chains, and so they form compartment.
- lipid bilayers are self-sealing because a hole in a bilayer is energetically unfavorable.
Can Water traverse membrane easily through the membrane?
yes. Its small size, high concentration and lack of a complete charge.
How are peropheral membrane proteins bound to membranes?
Bound to membranes primarily by electrostatic and hydrogen-bond
interactionswith the head groups of lipids (NOT EMBEDDED, LOOSELY ATTACHED)
Bound to the surfaces of integral proteins either on the cytosolic or extracellular side of membrane
OR
Anchored to the lipid bilayer by a covalently
attached hydrophobic chain, such as a fatty acid
How can peripheral proteins dissociate from membranes?
Dissociated from membranes by adding
salt or pH changes
Example of integral protein: Bacteriorhodopsin (light driven proton pump)
Example of peripheral protein: Cycloocygenase (COX1) or PGHS1
Explain the Three types of modification between lipid and protein linkages:
Palmitoylation
Farnesylation
Glycosylphosphatidylinositol-link (GPI)
KNOW that there is a way that proteins are linking to the lipid membrane (3)
Palmitoylation of cysteine residues by a thioester bond. (slide 22)
Farnesylation of cysteine residues at the C-terminus (slide 23)
**thioether linkage with Cys residue **
Glycosylphosphatidylinositol-link to the carboxyl terminus. (slide 24)
Anchors proteins to the OUTER leaflet of plasma membrane
What are the names of a mitochondrion’s two membranes and two compartments?
Outer membrane, Inner membrane (with cristae)
Intermembrane space (oxidative phosphorylation) , Matrix (site of TCA and fatty acid oxidation)
In a mitochondrion, where does oxidative phosphorylation take place?
inner mitochondrial membrane (intermembrane space)
