Membrane structure Flashcards
what is the cell membrane composed of? What holds it together?
Thin film of lipid and protein molecules held together by noncovalent interactions
what is an important characteristic of the cell membrane?
Fluid and dynamic (needs to move)
what is the cell membrane called? what function does it serve the cell?
lipid bilayer; impermeable barrier to water soluble molecules
since the membrane is an impermeable barrier, how is the cell able to receive substances? what are some general examples?
Transmembrane proteins mediate all other functions of membrane; transport, catalysis, structure links, receptor action
what makes up animal cell membranes? (percent)
50% of animal cell membranes are lipid, most of rest is protein
what term describes lipid molecules? what does it mean?
amphiphilic - hydrophilic polar and hydrophobic nonpolar ends - this forms bilayer
what are the most abundant membrane lipids? what do they look like? what are the main membrane lipids called?
phospholipids with two hydrophobic hydrocarbon tails (fatty acids); phosphoglycerides
in the three most common phospholipids found in mammalian membranes, what are their backbones made of?
backbone is a 3-carbon glycerol
what are the 4 common phospholipids called?
phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, sphingomyelin
one of the 4 common phospholipids is not like the rest, which one is it and what makes it different?
sphingomyelin; these are built from sphingosine, not glycerol
what serves as supportive region in the bilayer? how does it do this?
cholesterol and glycolipids; Cholesterol serves to increase impermeability of the lipid bilayer and prevents hydrocarbon tails from crystallizing (stabilizing)
how is cholesterol oriented within the phospholipids?
sterol is oriented with its hydroxyl polar head close to polar heads of phospholipids
how much lipid is the cell membrane composed of?
cell membranes have diff percent of lipids depending on their function
how does the membrane maintain its flexibility?
Lipid molecules in membranes are disordered(making it flexible); the spacing between them is irregular and flexible
why is fluidity of the membrane important? How does it maintain this?
for transport and enzymes to work; Lipid bilayer has bent tails to make the chains harder to pack together and the bilayer more difficult to freeze thus maintaining functionality at lower temps
what are lipid rafts? why do they form? what are they made of?
specialized domains; form transiently only when needed for protein transport or signal conversion; Made of specific lipids and proteins
what are the organelles lipid droplets used for? what do they contain? where are they formed?
Used to store excess cellular lipids, surrounded only by a phospholipid monolayer; contain neutral lipids like triglycerides and cholesterol esters; formed in the ER membrane
what is an adipocyte?
carry excess lipids; one big fat droplet
what does the lipid composition cause within the bilayer? what does this cause? what two reasons make it important?
asymmetry; Makes charges between the two halves of the bilayer different (providing electrochemical gradient for transport); crucial for converting extracellular signals into intracellular ones; also for marking dying cells
what are glycolipids? where are they found? what are their 3 functions?
sugar-containing lipid molecules found exclusively in noncytosolic side of lipid bilayer; help cell interact with its surroundings, protect from harsh surroundings, affect electrical field of membrane and ion concentration
where are sugars added to the glycolipids? why here?
Sugars are added in lumen of Golgi apparatus (environment similar to extracellular)
what are gangliosides? where are they found?
complex glycolipids found mostly in nerve cells
where can membrane proteins be located on the bilayer?
transmembrane- goes thru bilayer; intracellular/cytosolic- cytosol side of the bilayer; extracellular/noncytosolic - on cell surface
what role does a glycosylphosphatidylinositol (GPI) anchor play in transport? Describe the 3 steps the protein must take to reach its destination.
- Special membrane proteins that are extracellular are first made in the ER of the cell as single-pass initially
- Transmembrane segment is cleaved (part that helped it go thru membrane) and the GPI anchor is added instead (only hold protein has)
- Protein is delivered via transport vesicle to the cell membrane
how do peripheral membrane proteins attach?
bound via some noncovalent interaction with other membrane proteins
how are transmembrane proteins attached? How do they function?
held in the hydrophobic core of the lipid bilayer and cannot be released easily; function on both sides of the bilayer or transport molecules across it
how does the membrane-spanning domain (transmembrane domain) TMD work within the lipid bilayer?
outside of the bilayer is hydrophilic and inside of it is hydrophobic, so TMD are made of non-polar amino acids; the amino acids form hydrogen bonds with each other, so peptide chain curls into an alpha-helix as it crosses bilayer
what are single and multi-pass proteins?
Single-pass membrane proteins cross the lipid bilayer only once; multi-pass cross multiple times
what can multi-pass proteins form? what can this turn into? why is it done?
beta sheets; which form into a barrel; which is a protein to satisfy hydrogen bonding requirements
what are beta barrels also called? where are they more common?
porin proteins; bacterial and mitochondrial membranes
what are multi-pass proteins constructed from? what 3 functions do the constituents have?
constructed from alpha helices that can slide, open and shut, transport or transduce
how else can a beta barrel be used? what does it look like? what other function do they provide?
can form channels; may have amino acid loops that project into the center, filling the hole; may function as receptors or enzymes
what other structure can be used to form a channel? how is it done?
alpha helices; Multiple transmembrane helices can arrange to create channels through the membrane; function similar to porin proteins
what are hydropathy plots used for?
Illustrate the number of amino acids of a transmembrane protein (~20-30) and how many of these TMD are present
what does it mean to by glycosylated? where are these effected proteins located? are they always found here? where does glycosylation occur?
contain sugar; most cell membrane proteins; yes, sugars are always present on the noncytosolic side of membrane; sugars are added in the ER and Golgi to proteins destined for the membrane
where are carbs found on the cell? what protein can assist? what does this protein do?
coat the surface of all eukaryotic cells; lectins: carbohydrate-binding proteins; Mediate cell-cell adhesion processes and other recognition routes
what are detergents? what can they do? how can this be used?
Small amphiphilic molecules of various structure; Hydrophobic ends of detergents bind to hydrophobic regions of membrane proteins and pull membrane proteins into solution; Good for studying membrane protein characteristics and activities
what does it mean to have domains for proteins? what 2 variables make this possible? why is it done?
specialized regions where membrane proteins are segregated into specific areas of cell surfaces (each their own domain); 1. Proteins don’t swim through the lipids 2. Held in place by tight junctions, cytoskeleton, or protein-protein interactions; Keeps proteins AND lipids in appropriate places for specific functionality
what are the 3 types of protein-protein interaction used with the special protein domain?
◦ Self-aggregation
◦ Tethering
◦ Interaction with other cells
in red blood cells what protein tethers to the membrane proteins? what is the purpose of this protein?
spectrin protein; forms cell cytoskeleton; interacts with membrane proteins to produce a flexible membrane
what disorder does a mutation in spectrin protein cause? what effect does it have? what can it lead to?
Hereditary spherocytosis; produces RBCs that have unusual cell membrane properties (sphere shape) inflexible, destroyed quickly; leads to anemia
what do nucleated cells have that is analogous to spectrin’s function? where is it found? what is its purpose?
“cortical cytoskeletal network” more complex network that makes up the cortical region of the cytoplasm; Cytoskeletal filaments can be attached to cytosolic membrane and form barriers to avoid protein movement
what is the purpose of corralling proteins?
helps increase signal by concentrating activated signaling complexes
