Membranes Flashcards
*How is a lipid bilayer formed? what are the components and what is it’s hydrophobic effect?
Lipid bilayers are formed spontaneously (self-assembly) from phospholipids and glycolipids.
formation of the membrane is powered by HYDROPHOBIC EFFECT.
Hydrophobic effect- the tendency of nonpolar molecules to aggregate in aqueous solution and avoid water molecules.
*What factors dictate the permeability of a molecule through a lipid bilayer?
permeability based on size and charge of molecules and how SOLUBLE molecules are in water and lipids
permeability of small molecules based on their relative solubility in water and nonpolar solvents.
Lipid soluble molecules move easily across lipid bilayer
*How does temperature, length of the fatty acid, degree of saturation and cholesterol affect the transition temperature of a lipid bilayer?
melting temperature- is the temperature at which membrane transitions from being highly ordered to very fluid.
melting temperature is dependent on LENGTH of FATTY ACIDS in membrane lipid and degree of CIS UNSATURATION.
Cholesterol helps to maintain proper membrane fluidity in membranes of animals.
The longer the FA chain and more saturated, the higher melting temps required (to achieve liquid solution and fluidity).
whereas, shorter fatty acid, and more cis double bonds in chain lead to lower melting temp.
- Know the difference between integral membrane proteins and peripheral membrane
proteins. ‘
integral membrane proteins- embedded in hydrocarbon core of membrane
peripheral membrane proteins- bound to polar head groups of membrane lipids or to exposed surfaces of integral membrane proteins.
Some proteins are associated with membranes by attachment to hydrophobic moiety that is inserted into the membrane.
*Understand how “COX inhibitors” work. Provide an example of COX inhibitor
COX (cyclooxygenase) activity of prostaglandin H2 synthase 1 promotes production of prostaglandins
COX activity (convert arachidonic acid to prostaglandin H2) of the enzyme is dependent on a channel connecting to active site of membrane interior.
Hence, COX inhibitors like ASPIRIN inhibits cyclooxygenase activity by obstructing/blocking the channel.
This blocks the reduces affect of prostaglandins (INFLAMMATION, and pain)
aspirin creates block by adding ACETYL group to serine530 residue.
*Understand “lateral diffusion” in membranes.
Fluorescence recovery after photobleaching (FRAP) is a technique that allows the measurement of lateral mobility of membrane components.
Allows membrane proteins to diffuse laterally in membrane.
process:
membrane component attached to fluorescent molecule, and on small portion of membrane, dye is destroyed by high-intensity light, thereby bleaching a portion of membrane.
mobility of fluorescently labeled component is determined by how rapidly bleached area recovers fluorescence.
Lateral diffusion of proteins depends on whether they are attached to other cellular or extracellular components.
*What is the “fluid mosaic model” and how does it relate to the asymmetry of membranes?
Fluid mosaic model- 2D double layer structure of lipids and globular proteins that are constantly moving.
the difference in composition of carbs, proteins, lipids and cholesterol in fluid mosaic model relates to asymmetry of membranes because it explains its role for separating things in the inside from outside (permeability barrier).
*Understand the factors involved in transporting small molecules across a membrane.
Small molecules can spontaneously cross a membrane if two conditions are met:
1. concentration of molecule is higher on one side of membrane than the other
2. molecule is lipophilic (soluble) in nonpolar solutions
molecules who meet criteria can simply diffuse across the membrane.
*Compare lipophilic to polar (hydrophilic) molecules
Lipophilic- molecules that can easily pass through the membrane because they are soluble in nonpolar solutions (lipid bilayer)
polar molecules can diffuse across membrane DOWN their concentration gradient, only with assistance of protein called CHANNEL. movement is called FACILITATED DIFFUSION or PASSIVE TRANSPORT.
polar or charged ions cannot pass through hydrophobic interior of membrane on their own (need a transport protein)
*Understand the terms, membrane channel, facilitated diffusion and passive transport.
membrane channel- facilitates the flow of small molecules across the cell membrane. Channel is selective and specific of which molecules pass through.
facilitated diffusion or passive transport- occurs when a molecule moves DOWN its concentration gradient through a transport protein.
*How is a sodium gradient established across the membrane of a cell?
sodium must be pumped AGAINST concentration gradient, in the form of active transport as it requires energy (to move from low [ ] to high [ ] )
The Na+ K+ ATPase (Na+ K+ pump) uses the energy of ATP hydrolysis to simultaneously pump 3 Na+ ions out of the cell and 2 K+ ions into the cell against [ ] gradient. (how these ions are maintained).
since reaction includes intermediate in which enzyme is phosphorylated, pumps can also be called P-type ATPases.
*Understand the mechanisms of membrane antiporters and symporters.
Antiporters and symporters are secondary transporters that use one concentration gradient to power the formation of another.
Symporters- power transport of molecule AGAINST its concentration gradient by coupling the movement to movement of another molecule down its [ ] gradient with both molecules moving in the SAME direction.
Ex: Na+ Glucose symporter
Antiporters- use one concentration gradient to power the formation of another, but molecules move in OPPOSITE directions.
ex:
*What is digitalis and how does it work? Where does digitalis come from?
Digitalis- a cardiotonic steroid that strengthens heart contractions and are used to treat heart disease (heart failure)
digitalis inhibits the Na+ K+ pump by blocking its dephosphorylation.
one way of removing Calcium from cell is by Na+/Ca+ antiporter (sodium moves inside, to allow Ca to go out).
By inhibiting, Na+ K+ ATPase, Ca ions remain in the cell longer, leading to more robust heat contraction.
Digitalis- isolated from FOXGLOVE plant Digitalis purpurea.
*Understand the structure and function of an ion channel and know the different types. Also explain what Tetrodotoxin is.
Ion channels- passive transport systems that allow specific and rapid transport of ions DOWN their concentration gradient.
Types of channels:
1. Voltage- activated channels- activated by changes in voltage across a membrane
2. Ligand- activated channels- activated by binding of specific molecules (like neurotransmitters)\
Tetrodotoxin- toxin produced by the pufferfish, which is a lethal inhibitor of Na+ channel.
*Understand the nature of the potassium channel. How it operates, what the selectivity filter
is and how other ions are selectively blocked from moving through the channel
structure of K+ reveals the basis of ion specificity. The K+ channel selectively and rapidly transports K+ across the cell membrane. Larger ions are not transported because they are too big to enter channel. Smaller ions (like Na+) are excluded because they cannot interact with the selectivity filter. Such ions are small enough that energy of desolvation cannot be compensated for by interactions with selectivity filter. Selectivity filter of K+: K+ must release its water molecules when entering restricted part of pore, and energy must be compensated for this dehydration, Hence K+ is only ion that can make up for it by interacting with oxygen atoms of carbonyls in selectivity filter.
