Membranes I&II Flashcards
What controls membrane fluidity?
fatty acid composition and cholesterol content
List the common features of biological membranes.
Sheet like structures that form closed boundaries between different compartments.
Mainly, consist of lipids and proteins. They also contain carbohydrates that are linked to lipids and protein.
Membrane lipids have both a hydrophilic and hydrophobic unit (amphipathic).
Specific proteins are embedded in lipid bilayers and mediate distinct functions.
List the properties (other common features) of biological membranes.
form non-covalent assemblies
asymmetric
fluid structure
electrically polarized
List the two forms of membrane lipids.
Micelle
Bilayer
Describe a micelle.
limited, usually less than 20 nm in diameter
is formed when a variety of molecules including soaps and detergents are added to water
Describe a lipid bilayer.
favored structure for most phospholipids and glycolipids in water
self-assembly process
forces: hydrophobic interaction, Van der Waals, electrostatic, Hydrogen bonding
What is the driving force for self assembly?
hydrophobic interactions
What are the three significant consequences of membrane lipid hydrophobic interactions?
have an inherent tendency to be extensive
will tend to close on themselves so there are no edges with exposed hydrocarbon chains, and so they form a compartment
are self-sealing
True or False, lipid bilayers have a very low permeability for ions and most polar molecules.
True
What is the order from increasing permeability for molecules?
Na+, K+, Cl-, glucose, tryptophan, urea glycerol, indole, H2O
What are the types of membrane proteins?
integral (transmembrane) proteins, peripheral proteins, lipid-linked proteins
List the 3 kinds of modification for lipid-linked proteins.
Palmitoylation of cysteine residues
Farnesylation of cystein residues
Glycosylphophatidylinositol-link
What are the 2 specialized membranes of the mitochondria?
permeable outer membrane
impermeable inner membrane (matrix)
True or False, many integral membrane proteins extend across the lipid bilayer.
True
True or False the alpha helix is the most membrane spanning structure.
True
What forces bind peripheral proteins to the membrane surfaces?
electrostatic and hydrogen-bonding interactions
Where does oxidative phosphorylation take place in the mitochondria?
in the innermembrane space
What is the site of most of the TCA cycle and fatty acid oxidation?
in the matrix of the mitochondria
What is referred to by lateral movement of the membrane proteins?
Membrane proteins and lipids diffuse laterally along the membrane
What technique is used to observe the dynamics of membrane molecules?
FRAP = fluorescence recovery after photo-bleaching technique
How does transverse diffusion across the membrane compare to lateral diffusion?
Transverse diffusion (flip-flop) is very slow, while lateral diffusion is rapid.
What contributes to membrane asymmetry?
different composition of inner and outer leaflets
proteins have unique orientations
lipid molecules are asymmetrically distributed
large amounts of cholesterol in both leaflets
Why are carbohydrates placed on cell membranes?
glycosylation occurs on the extracellular surface of the plasma membrane
antibodies recognize RBC blood types by its extracellular carbohydrates
How do the membranes of eurkaryotes, bacteria and archaea differ?
Some bacteria and archaea only have a single membrane surrounded by a cell wall
eukaryotes, except for plants, have a lipid bilayer and no cell wall for their plasma membrane
Eukaryotic cells have _______ inside their cell membrane.
membrane bound organelles: peroxisomes, mitochondria, endoplasmic reticulum, golgi aparatus
True or False, eukaryotic nuclear envelope is continuous.
False
What must membranes be able to do?
separate and join together so cells and compartments can take-up, transport, and release molecules
What is another word for receptor-mediated endocytosis (RME)?
budding, fusion
Describe budding.
Invaginated membrane breaks off and fuses to form a vesicle
What is key for neurotransmitter release into the synaptic cleft?
fusion of a vesicle to a membrane
What does SNARE do?
gathers the appropriate membranes to initiate the fusion process
Describe mitochondrial fission.
Insertion of new components will cause mitochondria to grow
must be a signal for fission
mitochondria have to multiply to be divided between daughter cells
analogous to bacterial division
Describe mitochondrial fusion
occurs between identical organelles
excludes all other intracellular membranes
salvage process
requirements: sufficiently large electrochemical gradient must be present across inner membrane, elevated GTP levels must be available for hydrolysis
True or False, proteins have to be unfolded to be imported.
True
True of False, ATP is required if a protein crosses the matrix membrane.
True
