plasma membrane Flashcards
what is water potential
a measure of the tendency of water molecules to move from one area to another
what two structures does facilitated diffusion consist of
carrier proteins and channel proteins
whats a hypotonic solution
when the water solution outside the cell is higher than the water potential inside the cell thus water moves in
what molecules can easily diffuse across the phospholipid bilayer
small and non polar molecules
what molecules can pass slowly through the phospholipid bilayer
small polar molecules with a small difference in charge
why is the cell membrane described as partially permeable
charged particles (ions) and larger molecules are not able to pas through the phospholipid bilayer however, small and non-polar molecules can pass easily
what is the definition of facilitated diffusion
the net movement of particles from an area of high concentration to an area of low concentration across a partially permeable cell membrane via a carrier or channel protein (passive so doesn’t require ATP)
give an example of a molecule that can easily pass through the plasma membrane
O2 (small and nonpolar)
describe channel proteins?
form aq channels across the cell membrane which specific small, polar molecules(charged) can diffuse through
describe carrier proteins
the channel proteins can be open or closed depending on whether a specific ion is present - channel proteins are selective.
what do cells that require a lot of water have
special channel proteins called aquaporins
describe carrier proteins
some larger charged molecules require carrier proteins, this is where a specific molecule binds to the carrier protein, causing a change in shape known as a conformational change- catalyses molecules to be released
6 factors affecting rate of diffusion…
- temp
- conc grad
- sa
- diffusion distance
- size of molecule
- number of channel of carrier proteins
whats osmosis
the net movement of water molecules…
what does pure water have a water potential of
0
does a conc solution have a lower or higher water potential
lower
whats an isotonic solution
when the water potential of a solution outside a cell is the same as the water potential inside the cell
whats a hypertonic solution
when the water potential outside a cell is lower than inside a cell so water moves out
whats the fluid mosaic model
the different components present in the phospholipid bilayer.
- individual phospholipids can move= flexible
- mosaic=proteins (extrinsic and intrinsic) of different shapes and sizes are embedded.
what does cholesterol do
steroid molecule- regulates fluidity of the membrane
3 factors affecting membrane permeability
TEMPERATURE- high temp denatures membrane proteins- phospholipid molecules have more kinetic e and move further apart
PH- changes in tertiary structure of membrane proteins
use of a SOLVENT- may dissolve membrane
how do carrier proteins transport specific molecules?
by changing shape when the molecules bind to the protein
what are peripheral proteins held by
held by electrostatic forces
what are other important functions of peripheral proteins and integral proteins
- acting as receptors for drugs and hormones to bind
- acting as recognition sites for the immune system
- helping cells adhere together to form tissues
what’s a glycoprotein
proteins with a chain of carbohydrate molecules attached
what’s a glycolipid
lipids or phospholipids with a chain of carbohydrate molecules attached
what are the 4 main roles of glycolipids and glycoproteins
- acting as recognition sites for the immune system
- helping cells adhere to form tissues
- provide stability to the cell membrane
- glycoproteins act as cell receptors thus play a role in cell communication
describe the neds of cholesterol and what it does
hydrophilic and and hydrophobic end- regulates membrane fluidity
how does cholesterol prevent the membrane from becoming too stiff
prevents phospholipids from grouping together
how does cholesterol prevent the membrane from becoming too fluid
by interacting with the fatty acid tails of the phospholipids
why are membranes important (5)
- compartmentalisation provides protection
- contains different reactions for different metabolic reactions
- membranes involve proteins that are involved in chemical reactions.
- cell membranes are involved in the secretion of hormones and other chemicals that signal other cells.
- cell membranes also contain cell receptors that hormones and other chemicals can bind to
what happens to the phospholipids at a low temp
phospholipids= compressed= stiffened membrane
how can the compression of phospholipids be prevented apart from cholesterol
can be reduced by changing the amount of unsaturated and saturated phospholipid tails (kinks push phospholipids apart)
what type of phospholipids do animals living in cold environments have?
more unsaturated (maintains fluidity of plasma membrane- kinks push phospholipid molecules further away)
what happens to phospholipids at high temps
phospholipids gain kinetic energy and move further apart= increased fluidity and permeability= proteins drift sideways reducing their function ( at really high temp, protein= denatured)
what do organic solvents do to the phospholipid bilayer
disrupt the phospholipid bilayer and dissolves the cell membrane
at low conc= cell membrane more permeable to larger charged molecules
at high conc= destroys cells
