Cell Membranes Flashcards
what are 3 functions of the plasma membrane
1) barrier- controls what enters and leaves the cell
2) receptors on the surface allow “recognition” by other cells
3) Allow cell communication ( cell signalling)
substances can move across the cell membrane by diffusion, osmosis, active transport
why are membranes WITHIN cells good
1) membranes and organelles divide the cell into different compartments
2) can produce vesicles to transport substances between different areas
3) control which substances enter and leave the organelle
4) membranes within the cell can be the site of a chemical reaction- e.g. in the mitochondria there are enzymes in the inner membrane that are needed for respiration
why do they call it the fluid mosaic model
1) fluid- as phospholipids are constantly moving
2) mosiac- that’s the way the proteins are arranged and scattered throughout the bilayer
what is present in the phospholipid bilayer
1) cholesterol
2) Proteins
3) glycoprotein( protein mixed with carbohydrates)
4) glycolipids ( lipids mixed with carbohydrates)
how does the structure of a phospholipid link with the bilayer
they have a head and tail
head- hydrophillic- attract
tail-hydrophobic-
the molecules automatically arrange themselaves into a bilayer
where heads face out, tails face in.
the centre of the bilayer is hydroPHOBIC
so water soluble substances ( ions) cant pass through
why is cholesterol good for the membrane
provides STABILITY
cholesterol fits between phospholipids, and bind to their hydrophobic tails
allowing for them to pack more closely together
WHICH makes the membrane less fluid and more rigid
what do proteins do in the bilayer
1) some form channels in the membrane
2) transport substances by active transport or facilitated diffusion
3) act as receptors for cell signalling
what do glycolipids and glyco proteins do
1) stabilise the membrane by forming hydrogen bonds with surrounding water molecules
2) sites where drugs, hormones bind
3) act as receptors for cell signalling
4) Antigens (eg involved in the immune response0
why do cells communicate with eachother
cell signalling is a way for cells to control processes and respond to changes in the environment
how do cells communicate with each other?
1) cell releases a messenger molecule
2) This molecule travels to another cell
3) the messenger molecule is detected by the cell because it binds to a receptor on the cell’s cell membrane
what are membrane bound receptors
proteins that act as receptors for messenger molecules
shapes have to complementary to the messenger molecule to be able to bind
what are target cells and how do they work?
a taget cell , is a cell
that ONLY responds to a particular type of messenger molecule
1) messenger molecule binds to receptor on target cell
2) messenger molecule cant bind to receptors on anything else (i,e a non-target cell)
why histamine is a bad thing
one way to stop this is?
cell damage causes histamines to release
which bind to surfaces of other cells and causes inflammation
way to prevent this is to use:
antihistamines which work by blocking histamine receptors on cell surfaces, prevents histamine from binding
SO prevents inflammation
how does changing the temperature increase membrane permeability ( below 0 degrees)
for temperatures below 0 degree celcius:
- phospholipds have low temperature
- phospholipids are packed more closely together
- cant move- membrane rigid
- channel/carrier proteins deform, increasing permeability of the membrane
ice crsystals can form and PIERCE the membrane when it thaws, making it highky permeable
between (0-45 degrees)
- phospholipids can move around as they arent packed as closely together- so they have more energy
- membrane is partially permeable
