Membranes Flashcards
What is the basic structure of a membrane? and what is its function?
-lipids, proteins, and carbohydrates
-they separate the cell from it surroundings and compartmentalize the interior of the cells
What are the properties of membranes?
-MUST BE IMPERMEABLE(keep internal regions separate-lysosomes are acidic so they would dissolve the interior of the cell) (protect cell from elements)
-allow COMMUNICATION with outside world (proteins)
-EXPAND and CHANGE shape (allowing lipid and proteins mobility) (allow for white cells to insert pseudopods)
- IMPORT/ EXPORT specific ions/molecules (through channels and pumps)
-INTERACT with and RECOGNIZE the outside world (receptor, carbohydrates)
each organelle has its own set of lipids and proteins
membranes are made up mostly of _____
PHOSPHOLIPIDS
what is the composition of PHOSPHOLIPIDS? and how do they arrange?
-POLAR head that is HYDROPHILIC (loves water) and the tail is made up of NONPOLAR FATTY ACID chains (hate water)
- LIPID BILAYER: Phosphate heads will always face water, and phosphate tails will align in a way that will be hidden from water
What characteristics allow membranes to behave like a two dimensional fluid?
-Phospholids are not fixed to each other
-can spin, flex, and move laterally (can only move in 2 dimensions) within their own lipid bilayer
-almost NEVER flip to other membrane leaflet
When might Membrane proteins (and lipids) floating in the fluid lipid bilayer and diffusing within the membrane be important?
-Lipids and proteins can easily diffuse from their original membrane insertion sites (to allow them to be exposed to different parts of the environment)
-Enables interactions between membrane proteins
-ensures even distribution of molecules between daughter cells after MITOSIS
Membrane fluidity is dependent on ______ and it can be modified by ____
1.lipid composition
- -the amount of saturated and unsaturated hydrocarbon tails
- UNSATURATED hydrocarbon tails are MORE fluid/flexible and permeable
**cells can have different portions of each of the types of carbon tails
- -Inserting cholesterol between each UNSATURATED hydrocarbon, allows for it to stiffen the bilayer and makes it LESS PERMEABLE and LESS FLEXIBLE and it ALSO protects membrane from freezing (crystallization) 3
4.
what makes UNSATURATED hydrocarbon tails MORE fluid?
- DOUBLE BONDS between carbon atoms creates kink , SO they can’t PACK AS TIGHTLY together as straight saturated hydrocarbon tails
What is a lipid raft? and what is its purpose?
- cholesterol rich regions that compartmentalizes cellular processes (assemblies of proteins and lipids that are stuck together and are less permeable and flexible)
-these are used to unite proteins that are meant to work together
-TOO much cholesterol in can cause disease- can be hijacked to cause disease
when is it ideal to limit diffusion of lipids and proteins throughout the entire cell membrane? And how can this be done?
-when proteins have important jobs and need to be at the top of the membrane to be able to Carr you their work (epithelial cell)
- localize proteins on lipid rafts
- connection to another cell by junction (tight junctions on lateral top membrane side-prevent movement of proteins around the corners)
- connection to cytoskeletal anchor proteins (anchor desired proteins)
- connection to extracellular matrix
Where are new phospholipids (membranes) produced? and what is the process?
- SMOOTH ENDOPLASMIC RETICULUM
- made on the CYTOSOLIC SURFACE where synthetic enzymes are bound
2.There enzyme SCRAMBLASE randomly moves phospholipase from one leaflet to ER membrane to the other
**END RESULT: both membrane leaflets are pretty much the same
3.membrane is then brought to the golgi apparatus for modification (INSIDE” and “Outside” faces)- modified proteins and lipids (ALTER LIPIDS TO CREATE ASYMETRICAL MEMBRANE)\
-Sugars added always face extracellular space (glycolipids and glycoproteins) FORMING GLYCOCALYX
-negatively charged phospholipids remain on cytosolic side creating MEMBRANE POTENTIAL
What does the Golgi apparatus do to the membranes?
-creates asymmetrical plasma membrane
**modification (INSIDE” and “Outside” faces)- modified proteins and lipids (ALTER LIPIDS TO CREATE ASYMETRICAL MEMBRANE)\
-Sugars added always face extracellular space (glycolipids and glycoproteins) FORMING GLYCOCALYX
-negatively charged phospholipids remain on cytosolic side creating MEMBRANE POTENTIAL **
-Sends vesicles to their final destinations
Membrane transport often depends on ____
specialized membrane transport proteins
What proteins can pass through membranes readily by themselves?
- O2,
-thyroid hormones,
-CO2, - N2
-steroid hormones
what are the mechanisms for moving solutes across membranes? (can be passive or active)
-ENDOCYTOSIS and EXOCYTOSIS (membrane folding) – SLOW PROCESS
-TRANSPORTERS (bind to molecule and undergo transformational change to transfer colure across membrane)- FAST and relatively specific
-CHANNELS (form aqueous pores that allow solutes to quickly cross membrane- FASTEST -relatively specific (ex. aquaporins - just allow water through)
What is diffusion?
is a spontaneous movement of particles down their OWN concentration gradient
- Particles move from high concentration to an area of low
concentration.
Na electrochemical gradient favors movement of Na in which direction?
IN
-often brings OTHER molecules along with it
What is K+ more likely to do when faced with an electrochemical gradient?
-Chemical gradient says go out BUT the electrical gradient says stay in– CONFLICTED
-chemical gradient wins a little
Movement through channels can be passive…..
- meaning that is is just based on the chemical gradient
-HIGH to LOW concentration through transporter or a channel
movement through channels can be ACTIVE…
-meaning movement is AGAINST its own ELECTROCHEMICAL gradient
- PRIMARY ACTIVE TRANSPORT: ATP needs to be used to force molecule into the cell through the use of PUMPS (NA+/K+ pump -> tap keeps sodium out of cell, H+ pump, Ca2+ pump)
may result in imbalance of solute
-SECONDARY ACTIVE TRANSPORT: Electrochemical gradient of one analyte
(e.g. sodium) is used to drive the movement of another analyte (e.g.
glucose).
* NO ATP - ONLY USE sodium gradient to drag other molecules in with sodium* COUPLED TRANSPORT
What are the types of transport observed in the image?
- ANTIPORTER- PRIMARY ACTIVE TRANSPORT (not relying on concentration)
- SYMPORTER- SECONDARY ACTIVE TRANSPORT (relying on sodium gradient not concentration)
- UNIPORTER PASSIVE TRANSPORT (relying on transportation)
What type of transporter prevent glucose from moving back into the intestinal lumen during fasting?
Glucose-Na+ symporters prevent glucose from
moving back into the intestinal lumen during
fasting
Na/K transporter in the
basolateral membrane expels Na
how can channels be open?
- Voltage-gated ion channels open
when a certain membrane
potential has been reached. - Ligand-gated ion channels open
when a specific ligand binds to
the channel - Mechanically-gated ion
channels open when mechanical
force applied to the channel. (least common– seen in inner ear, when fluid passes the protein opens the channel– used to hear and balance)
