Bio Exam II. 2

• does not span the bilayer; it is located in 1/2 of the bilayer
• how much depends on the animal membrane (there is none present in fungi, plants, and bacteria)

• hydrophilic (nestled up against the -OH in the membrane)
• the rest of the molecule is hydrophobic
• forms more than one hydrogen bonds with lipid portion

• rigid
• adds rigidity to membrane
• - at higher temps it makes the membrane more rigid
• decreases permeability of membrane (lipid bilayer) to ions, small polar molecules, etc. [if they do get through, it is with the help of proteins]

lowers transition temp by decreasing fluidity (it'll be harder to pack the lipid molecule together)

• at higher temperatures, because of rigidity, it decreases fluidity
• at lower temperature, it adds fluidity

• rigidity
• mechanical strength

• cholesterol
• sterol

stay fluid just as animal membranes must

• - proteins will slow down lipid movement due to interactions with other proteins. It will either stop them or slow them down. 
• - temperature (if no regulation, temperature of membrane is same as environment)
• - fatty acid chains and the distance between them
• - not much surface area--> slows them down
• - proteins move way slower (their size affects fluidity)
• - cytoskeleton and attachment will stop it by anchoring the molecule in place
• - extracellular matrix will slow down or stop if the proteins are attached
• - protein complex--> slow movement

their own thermal energy

• permeability facilitation (even though there can be a leak in the lipid bilayer between the bilayers)
• exocytosis, endocytosis
• flexibility + order (membrane is the midpoint), mitosis, meiosis, growth
• regulation of interaction (you don't want proteins to ALWAYS interact; fluidity allows them to come together)
• - lipid composition change based on temperature

most, if not all, membranes

• carbs (usually stick out only in EM)
• protiens are asymmetrical, as well as lipids

• phosphatydylinositol: found inside facing cytosol
• phosphatydylserine: found inside facing cytosol
• phosphatydylcholine: outer part of the bilayer facing the EM
• the cytosolic surace

False: not easy

• made inside ER, goes to vesicles, and fuses with plasma membranes, going to the outer leaflet by flip flopping. 
• Flip flopping is very rare; PC is helped by proteins called flipases

lateral movement is more rapid than flip flop movement

• lipids
• cholesterol
• within a cell that has a ton of it as opposed to one that does not

functioning

• barrier and compartmentalization
• regulation of movement in and out of compartment
• mechanical strength
• access to info and interaction with envi.
• fusion/ splitting of cells and vesicles
• interaction of cells and organelles with one another 
• allows cell to organize (site of some biochem reactions)
• site of energy conversions
• electrical insulation
• cell movement
• cell shape

• lipid bilayer does this; whaevter is inside usually stays in; out stays out unless you have help
• benefit: have internal environment different from outside
• compartmentalizes cytoplasm

• proteins do this
• if something does not readily move and has no protein to help, it will not get through; allows control

• lipids nad proteins
• proteins

• glycoproteins
• recognition 
• interaction
• receptor-mediated endocytosis
• cell-cell recognition and adhesion

• phagocytois: changes shape and moves out around cell; pushes inward; unspecific
• pinocytosis: no receptors; membrane pushes inward; unspecific

material inside a depression, which splits from membrane

• Receptor proteins on surface that will specifically bind those components to the receptor
• Allows uptake of things available in low concentration in environment
• - will result in increased concentration in cell

in packets of about 1500 cholesterol with some protein

by liver's hepatocytes and secreted by liver

make membranes; they would take in the packets

• LDL 
• HDL: more proteins; take cholesterol back to the liver where it gets destroyed

make receptors

• receptors associate in forming pits before anything
• receptors get stuck in pits and bond to LDL
• If the pit is deep enough, it breaks off--> becomes a coated vesicle because clathrin is always there on the outside

• vesicle wants to get rid of clathrin; now able to fuse with lysosome or endosome
• if not removed, the clathrin gets in the way of the binding

the food is broken down to substituents--> able to be used

without Clathrin, there is no Receptor mediated endocytosis; it is needed to form pits

• its a feedback loop
• it turns off the LDL receptor synthesis and cholesterol synthesis

receptors are recycled back to membrane (some systems don't do that)

• oversupply of cholesterol in bloodstream--> plaque in arteries (usually at site of injury, etc.)
• - reduces elasticity and diameter--> strain on heart

• mutations that affect binding site (bind something it isn't supposed to_
• cell just dones't make them
• shape change so it cant be inserted into membrane 
• cant bind clathrin and get caught/ accumulate in pits
• can't be recycled