cell membrane Flashcards
functions of cell membrane
- Membranes establish a boundary around all living cells
Involved in transport processes: lets cell bring in things it wants to bring in
organization
cell to cell communication
signal detection
what does railroad track appearance of membranes refer to?
phospholipid bilayers lined up next to each other with intercellular space in the middle
what are the 3 kinds of phospholipids?
Phosphatidylcholine (PC)
Phosphatidylethanolamine (PE) Phosphatidylserine (PS)
what is the asymmetrical distribution of a cell membrane?
different phospholipids are on the outer side of the membreane vs inner side. More PC facing outside and more PE facing inside (no flipping to other side!)
glycolipid
lipid + glycerol
which way do sugars face in the cell membrane
always face out!
how does saturation affect fluidity?
the more unsaturated you are, the less tightly you’re packed, the more fluid you are
how is cholesterol related to fluidity?
sits in between phospholipids prevents them from totally moving around
Frye & Edidin
The quick mixing of the fluorescent labels means that the proteins that are on the surface of the cellare not fixed in place – they can and do diffuse rapidly around the exterior of the cell, while still being embedded in the plasma membrane. This realization led to the development of the fluid-mosaic model
fluid mosaic model
the plasma membrane as a bilayer, two layers of lipid molecules, with protein molecules embedded in the layers. They compared this to a mosaic of colored tiles that are inlaid to form a design or picture. However, in this case, the tiles are the molecules of lipid and protein, and they are not fixed in place – they move about through diffusion
which layer of the lipid bilayer is fluid and moves?
outer layer
describe the integral proteins and their structure
integrin are trans membrane proteins, go all the way through the lipid bilayer and are composed of alpha helices
where do you usually find cholesterol and what does it do?
inserts itself between phospholipids, in the membrane- its a buffer. maintains the fluidity of our membrane
integral protein crosses how much of membrane?
goes all the way through
what’s a peripheral protein?
sits either right on top or just below membrane
whats the ratio of proteins: phospholipids ?
1:1
why are there proteins in the membrane?
receptors- tell cell whats going on
transport molecules in/out of cell
function of sugars in the membrane
recognizing other cells
what kind of protein would a hormone be?
peripheral protein- attach, make cell do something, and then leave
lipid bound proteins
sits in between layers- very very rare!
what does a channel or transport protein look like and do?
allow different materials from outside environment into the cell, and bad stuff from cell outside. ex: Na ion pump
receptor protein
trans membrane protein that carries things inside and outside of cell using a binding site called ’binding domain’ . These guys always have some sort of target molecule to bind to: called ligands. usually 7 trans membrane domains per protein. sometimes brings energy/ATP.
what is a transmembrane domain?
transmembrane proteins have hydrophobic regions called transmembrane domains that are generally made of alpha helices
what does having a pore in the transmembrane signal?
that you would have hydrophilic side chains here
what holds the inside of the cellular membrane together?
fibrous linking proteins such as spectrin
glycocalyx
‘sugar halo’ The glycocalyx is a glycoprotein covering that surrounds the cell membranes of some bacteria, epithelia and other cells. Most animal epithelial cells have a fuzz-like coat on the external surface of their plasma membranes.
what is glycocalyx composed of?
oligosacchardies linked to membrans
Cortex
- outer layer of a biological structure. Ex: a kidney will have an outer portion called a cortex- still inside but out near the edges of the cell.
can all membrane proteins move around?
no. some are tethered to cell cortex, ECM, or the side of another cell
passive transport
moving down or ‘with’ concentration gradient
selective permeability
more- or less- permeable depending on which kind of molecule you are
which way does a gradient go?
from high concentration to low concentration
why can’t Na+ ions passively diffuse?
attracted to charged polar head, but wouldn’t be able to make it through the tail
what types of molecules can pass through the cell membrane without any assistance?
small uncharged ones; CO2, H2O, ethanol, N2 etc.
can sugars passively get through the cell membrane?
no- need help from a protein
what is aquaporin?
how H2O gets passively through cells
what is facilitated diffusion?
passive transport thru carrier or channel proteins
carrier proteins
type of facilitated OR active diffusion, mostly for sugars and amino acids, where the molecule in question sticks onto the protein it changes conformation and dumps them out on the other side. passive /active transport
channel protein
a protein that allows the transport of specific substances (IONS) across a cell membrane. ex: sodium potassium pump
why does facilitated diffusion demonstrate saturation?
if the proteins carrying things are all filled up already- process slows and stops
Na+ concentrations in and and out of your cells
high sodium concentration outside, low inside. In the range of 10x.
K+ concentrations in/out of your cells
Potassium: high inside, low outside (30x).
what can you say about calcium concentration in cells?
calcium tends to be highly regulated b/c important for other cellular processes such as muscle function
active transport - and is it saturable? protein specific?
- Active Transport: works against the gradient, requires energy. Moves stuff from from inside -> outside against the gradient, using energy. Still saturable, still protein specific.
uniport
A uniport carrier is a membrane transport protein that moves only one kind of molecule.
why is a channel protein always passive transport?
its just a tunnel! lets things go through according to their gradient
symport
bring 2 different molecules both from one side to the other side
antiport
type of coupled transport that brings in 2 diff molecules- one from each opposite side of gradient to the other
types of active transport- by function
coupled transport (symport/antiport), ATP pump, or light-driven pump
energy difference ADP vs ATP
ADP has lower energy by 7.3 kcal/mole. This keeps equilibrium on the ADP side- it’s a spontaneous reaction energy wise
what’s the classic example of the ATP pump type of active transport?
Na+/K+ pump
how does the Na+/K+ pump work and what protein/energy events happen that drive this?
-antiporter that pumps 3 na+ out, 2 K+ in, actively (against their gradients )
- Binding sites for Na+, K+ & ATP to do this
- Covalent attachment of phosphate to the protein (and subsequent removal) cause conformational changes that drive the process
Na-glucose symport
coupled active transport that has a carrier proteins bind to both sodium and sugar, uses the sodium gradient to shift positions and dump the sugars out on other side, in the cell. Sugars brought in against their gradient. Na+ gradient used as a form of potential energy. It’s a symporter bc bringing 2 diff things in. common method in intestinal epithelial cells
once you’ve pumped glucose in with sodium into your gut- how do you get it out?
passive transport, uniport, like a channel protein
Intracellular Glucose kept high by_____
Na/Glucose symporter
Intracellular Na+ kept low by_______
Na/K ATPase (pump)
are ion channels regulated? describe the process behind their opening and closing
highly regulated, likea nuclear pore- gates. Different ions and conditions influence opening and closing of ion channel proteins. often voltage/ligand gated
what is vesicle inversion?
when vesicles fuse, their outer phospholipids end up in exterior of plasma membrane! Flipped! This means tht in vesicles, need to put specific phospholipids on the inside, like only PC .
phagocytosis vs pinocytosis vs Receptor mediated endocytosis
phagocytosis ‘cell eating’ particles not fluids, (fuses with lysosome) pinocytosis ‘cell drinking’ just taking in fluids. ‘receptor mediated endocytosis’ , takes in receptors that bind to specific things.
what is clathrin
a protein that assists in receptor mediated endocytosis
- Clathrin lines the membrane just beneath the receptors, and once the receptors are full, clathrin assist in the infolding like a motor.
receptor mediated endocytosis- how does this process work?
area with receptors molecules Signals clathrins to do infolding.
Once infolding is completed clathrin falls off and recycles themselves back up to the membrane.
cargo Comes down as endosome fuses with a lysosome and starts digesting its cargo.
Pushes most of receptors on one side, allows to bud off and head back up to membrane.
Keeps the cargo, lysosome digests it-monomers move out into cytoplasm via facilitated diffusion.
what are some ligands that undergo receptor mediated endocytosis?
target ligands that do RME: iron, vitamin B, and cholesterol LDL
LDL vs HDL?
- HDL is the good kind!!! LDL causes heart attacks due to plaque buildup.
how would clathrin be related to LDL?
its the protein that flushes your blood clean of bad cholesterol by causing your membrane to seal around it in a vesicle and send it to the lysosome
difference between diffusion and passive diffusion?
diffusion: h20, co2 other uncharged tiny guys just meandering through. passive is actually using a channel or carrier
