transport into and around the cell Flashcards
what is the function of a membrane?
separates cells from their external environment
also defines spaces
functions of membranes
transport enzyme activity signal transduction intercellular joining cel recognition attachment to ECM
what is the membrane structure?
very thin 2 molecules thick forms a closed boundary made of lipids proteins embedded in the layer
why are proteins found in membranes
give the membrane function and ability to do certain tasks
what is a bacteria membrane like?
can have multiple ones and cell walls
different composition but same lipids
what are virus membranes like?
enveloped viruses with lipid layer from the cell in infected
how does the fluid mosiac model describe membranes?
a mix of lipids in layer that move around in flux
proteins are embedded within too
membrane is flexible
what is the evidence for the fluid mosaic model?
surface tension of the membrane did not match that of lipid only models but did match when proteins added
how did evidence for the fluid modaic model come about?
fused mouse and human cellls together in a hybrid
proteins mixed and moved therefore they are fluid and can move proving the fluid mosaic modeel
examples of lipids
cholesterol
phospholipids
glycolipids
what is special aboout lipids?
each organ and organelles has a differnt composition of them and the types
why is pH key for membranes?
ensures head groups are in their ionised charged form and thus suitably hydrohobic
what is self assembely?
if phospholipids are added to a tube of water a neural pH they will spontaneously form a closed bilayer in structures called liposomes
what is a phospholipid?
phosphate containing two lipids
two fatty acid chains with a glycerol backbone
what is the difference between a phosphoglyceride and a sphingolipid?
phosphoglyceride is glycerol base lipid
sphingolipid is sphingosine bases lipid
if the membrane is too cold and rigid what changes does it make?
more unsaturated lipids, adds kinks to the tail to space out molecules
proteins can move around and membranes become more fluid
if the membrane is too hot and fluid what changes does it make?
lipids become more saturates and packed more tightly making the membrane more fluid
what does adding cholesterol to a membrane do?
controls the fluidity of the membrane
but too much makes it rigid and viscous
how is the membrane asymmetrical
outer layer is different to inner
eg receptors
what are found on the outside of the membrane?
glycolipids
what is a glycolipid?
sugar group headed lipid
what is the function of a glyocolipid
provides protection for the cell sugar coating.
helps with ice crystals and stresses
what is found on the inside of the membrane?
phosphatidylserine
what is the function of phosphatidylserine
signal molecules
flips over during death signals to act as the signalling molecules for death and that the cell needs to be engulfed and disposed of
process called flip-flop
what causes flip-flop movement?
very rare
enzymes called flippases can sometimes do this but its never spontaneous
how does the membrane have an electrical charge?
inside the cell are proteins and ions that at a neural pH have a new negative charge
the ions move in and out of the cell to balance this charge out
causes and electrochemical gradient
what is the gradient in a cell
positive outside
negative inside
why is the electrical gradient in cells so important?
nerve signal transmission requies it
what does the membrane favour in terms of ions?
transport of cations into the cell
anions out
how do things move across the membrane?
it is selectively permeable
highly controlled what goes in and out
what can and cant go across membranes
hydrophobic moecules cant disolve
sugars are repelled
what facilitates movement of thing across the membrane
transport proteins
channel proteins
why are transport protens used?
a hydrophillic substance that cant go through on their own
what transport water?
aquaporins
how do carrier proteins work?
bind to molecules and change shape to shuttle things across the membrane
not open all the time, specific
works down a concentration gradient, passive
what is passive transport?
diffusion
carrier proteins
how does active transport work>
against a concentration gradient
requires energy in form of ATP
what do cells contain that remain largely trapped within the cell?
sugar protein amino acids nucleotides ions
because there are lots of things within the cell it creates a what gradient?
strong osmotic gradient
meanign water will move into the cell
how is the osmotic gradient controlled?
Na/K pump
how does the Na/K pump work?
pumps out some ions
open on the outside and removes sodium through ATP
open on the inside too allowing K to bind
3Na out for every 2K in
net loss from cell and equalibrium made
why is endocytosis used in cells?
cant have large channels for large molecules because then everything smaller would also flow through
so endocytosis is used
describe the process of receptor-mediated endocytosis
- ligand binds to membrane receptor
- receptor-ligand migrates into clathrin-coated pill, membrane pulls molecule into cell
- endocytosis
- endosome/vehicle made with molecule inside losing clathrin coat
- enzymes degrade lipids
how does the process of coated vesicles in endocytosis work?
ligand binds to receptor
membrane curves a proteins bind to inside of receptor fitting together to form a circle endosome
in a coated vesicle endosymbiosis what is the endosome coated in?
clathrin molecule forms a cage/coat
what is pinocytosis?
takes in little bits of the environment
how are proteis secreted?
transported to the plasma membrane in vesicles which then fuse with the membrane releasing their contents
what balance keep cells shrinking?
endocytosis and exocytosis
where are proteins synthesised?
rough ER
where are proteins packaged?
golgi body
what are the two pathways for a substance to be secreted?
constitutive secretory pathway
regulated secretory pathway
how does the constitutive secretory pathway work?
used immediately and constantly made
used for molecules to be secreted as soon as they are made
the molecule is packaged and sent to surface quickly to be secreted
the membrane fusion is unregulated
how does the regulated secretory pathway work?
the packaged molecule stays around for a while
it is stored and only released when it recieves the correct signal such as a hormone or neurotransmitter
made in advance to save time
how do viruses exploit membrane transport
use the host membrane to get in and out of the cell
ligands on virus cell iminates the cells ones
fools the cells and allows it to undergo endocytosis
enzymes on the virus protect it from being degrades
budd out taking some membrane with it
what helps viruses fool cells?
ligands on surfaces and lipids
what are cellular membranes and why are they imporant
golgi and ER
key to move things around the cell once inside
compartmentalisation of cells
how do proteins end up where they need to be?
labels on they act as tags to signal where they need to be sent
what signal sends a protein to the nucleus?
lys-lys-lys-arg-lys
how can proteins be modified after being made
glycosylated
phosphylation
ubiqunation
a glycosylated protein goes where?
plasma membrane
a phosphylated protein can do what?
change what it can bind to
what does unbinquination do to a molecule?
sends the protein for break down in the proteosome
how can you move things between compartments
gated transport
transmembrane transport
vesicles
how does gated transport work?
eg nuclear pore
acts like a channel proteins allowing large things through
needs sequence tagging to work
how does transmembrane transport work
cant have a large pore to move proteins so this allows single amino acids through at a time
acts as a proteins translocator an the peptide chain is fed through
example of transmembrane transport
mitochondria
moving cytochrome C around
exmple of vesicular transport
motor proteins
why is vesicular transport needed?
vesicles need to be moved around the cell to they are waked down microtubues
three types of motor proteins used to transport vesicles?
- myosin
- kinesin
- dynein
which motor protein used actin filaments?
myosin
which motor proteins use microtbules
kinesin and dynein
which motor protein moves things towards the edge of the cell
kinesin
which motor protein moves things towards the middle of the cell?
dynein
what do motor proteins move?
vesicles and whole organelles
drag chromosomes durig mitosis
what do endosomes use to move?
dynein
what do secretory vesicles use to move?
kinesin
how do nerve cells use motor proteins?
transmitting nerve signals they need they neurotransmitter down the other end to where its mad
use mtoro proteins to move it where its needed
what do motor proteins require to work?
ATP
structure of a motor protein
head/feet
stalk
tail attaches to the molecules to be moved
add ATP to head/ foot to move in a step like way
