Lecture 16- Biological Membranes Flashcards
What are the 2 major components of all membranes?
Which composes a majority of a membrane?
Lipids and Proteins
Lipids
Functions of a Biological Membrane:
- Defines _______ boundaries of a cell
- Controls molecular ______ across boundary
- Divide cells (_______) into ____________
- Organizes ________ sequences
- ____-to-____ communication
- Matrix for _________, ________, _________ molecules
- ________ transduction w/in cell (________, ________)
Functions of a Biological Membrane:
- Defines external boundaries of a cell
- Controls molecular traffic across boundary
- Divide cells (eukaryotes) into compartments
- Organizes reaction sequences
- Cell-to-Cell communication
- Matrix for transporters, receptors, adhesion molecules
- Energy transduction w/in cell (mitochondria, chloroplasts)
Amount of Å a lipid portion of a bilayer is?
2 monolayers of a bilayer?
30 Å
Leaflets
1 wedge-shaped fatty acid tail consisting of a fatty acid/lysolipids
Micelle
2 cylindrical fatty acid tails (Glyerophospholipids, Sphingolipids)
Combo above that contains an aqueous cavity
Bilayer
Vesicles
Concentration of lipid req’d for micelle formation
Critical Micelle Formation
What do the formation of micelles depend on? (3)
Temp, lipic concentration & lipid composition
What is a vesicle prepared from purified lipid?
Liposome
T/F: Lipid composition of all cell membranes is the same.
(Explain)
False: Lipid composition of cell membranes is different depending on organelle and function.
LIpid composition of bilayer leaflets is (bisymmetrical/asymmetrical) w/ _______ lipids and/or ________ on the ________ leaflet.
LIpid composition of bilayer leaflets is asymmetrical w/ neutral lipids and/or glycolipids on the external leaflet.
What kind of model best describes biological membranes?
This can be described as a non-rigid, complex mixture of _______ & ________ molecules ______ in bilayer
Fluid Mosaic Model
This can be described as a non-rigid, complex mixture of lipids & protein molecules floating in bilayer
The interior of a bilogical membrane is consisted of _____ ______ that forms a _____, ___________ region.
The interior of a bilogical membrane is consisted of fatty acyl (C-H) that forms a fluid, hydrophobic region.
___________ interactions of ____ side-chains hold membrane proteins together.
Hydrophobic interactions of AA side-chains hold membrane proteins together.
What type of membrane proteins are the site of hydrophobic AA interaction and are only reremovable by hydrophobic agents (EX?)
Integral Membrane Proteins (Removable by hydrophobic agents: detergents, organic solvents, denaturants)
What type of membrane proteins associate with electrostatic interactions with H-bonding and how are they released?
Peripheral (mild detergents/interference w/ charge or H-bonding)
What type of membrane proteins is located in the cytosol that can associate/dissocate thru electrostatic interactions/lipid tails? (EX)
Amphitropic Proteins
(Covalent/Noncovalent = Lipidation, phosphorylation, ligan binding)
What is the localization of proteins relative to the lipid bilayer and how can it be assessed?
Membrane Protein Topology, analysis of AA sequence
What are common transmembrane motifs within membrane protein topology?
What do proteins have that is important to distinguish its function?
Alpha helices and Beta-strands
“Sidedness”
For protein-lipid interactions, how are membrane proteins classified? (4)
Sidedness, # of transmembrane (TM) helices, # polypeptides, lipid modifications
Type of protein-lipid interaction that has a single TM helix & Amino-terminus on the outside?
Type 1
Type of protein-lipid interaction that contains a single, TM helix & carboxy-terminus on the outside?
Type 2
Type of protein-lipid interaction that contains multiple TM helices?
Type 3
Type of protein-lipid interaction that contains multiple, polypeptides that assemble to form protein complexes?
Type 4
Type of protein-lipid interaction that is attached to the bilayer primarily by lipid modification?
Type 5
Type of protein-lipid interaction that contains BOTH terminal helices and lipid anchors?
Type 6
____________: Type 3 Integral Membrane Protein
- Salt-loving bacteria similar to light-driven molecule in ___ that absorbs protons
- __ TM helices connected by the inner non-helical loops & outer face membrane
- Anchored by hydrophobic ____ _____ interactions with _______
Bacteriohodopsin: Type 3 Integral Membrane Protein
- Salt-loving bacteria similar to light-driven molecule in eye that absorbs protons
- 7 TM helices connected by the inner non-helical loops & outer face membrane
- Anchored by hydrophobic side chain interactions with lipids
Predicting Secondary Structure of Membrane Spanning Portions of Integral Membrane Protein:
- Alpha-helix: ___ Å rise/residue
- 30 Å hydrophobic interior req’s __ AA
- TM helices ~__ turns long
Predicting Secondary Structure of Membrane Spanning Portions of Integral Membrane Protein:
- Alpha-helix: 1.5 Å rise/residue
- 30 Å hydrophobic interior req’s 20 AA
- TM helices ~6-7 turns long
What is the amount of energy it takes to move an R group from the hydrophobic to hydrophilic area? (Delta G)
Hydropathy Index
For a hydropathy index, a (+)Delta G requires energy, which indicates a __________ group.
hydrophobic
Type of graph?
Label the axes.
A Hydropathy plot contains successive windows of sequence with the calculated hydropathy index and then its residue number plotted against it.
What are aromatic residues found @ the interface of water and lipids?
Name 2 that are also found bw exterior & interior, and @ border.
Membrane Interface Anchors
Tyrosine (Y) & Tryptophan (W)
Positive-Inside Rule for Membrane Proteins:
- (-) charged lipids are usually on the ______ leaflet (phosphotidylserine/phosphotidylinositol)
- Favors (+) charged AA (___, ____, ____) on the inside
- Look for charge in ___________ regions to determine orientation
Positive-Inside Rule for Membrane Proteins:
- (-) charged lipids are usually on the inner leaflet (phosphotidylserine/phosphotidylinositol)
- Favors (+) charged AA (Lys (K), Arg (R), His (H)) on the inside
- Look for charge in non-transmembrane regions to determine orientation
__-________: another structure found in integral proteins
- ___________ inside barrel
- ___________ outside barrel (touching ______)
- Important for _______ transport, but hard to determine
- _______: proteins that allow select polar solutes to cross membranes
B-Strands–> B-Barrel: another structure found in integral proteins
- Hydrophilic inside barrel
- Hydrophobic outside barrel (touching lipids)
- Important for passive transport, but hard to determine
- Porins: proteins that allow select polar solutes to cross membranes
_____________ membrane proteins can associate w/ membranes by covalently attached lipids
- Not integral/peripheral, but how are they attached? (aka?)
- What is the strongest? (2x16C’s)
- _______ = Strength!
Amphitrophic membrane proteins can associate w/ membranes by covalently attached lipids
- Not integral/peripheral, but attached by anchors of lipid molecules to target proteins (posttranslational modification)
- Glycosylphosphatidlyinositol, GPI is the strongest (2x16C’s)
- Length = Strength!
