transport across cell membranes Flashcards
(32 cards)
membranes
-all cells and organelles surrounded by a partially permeable membrane
-controls the movement of substances in and out
-contains receptors
protection
-phospholipid bilayer, hydrophobic head and hydrophilic tail
-fatty acids chains saturated or unsaturated
-allows small non polar molecules the ability to move between
shape
-cholesterol allows the membrane to maintain its shape and stability
-binds to the polar heads and non polar tails to restrict movement
-prevents leakage of water and dissolved ions
food in/waste out
-the permeability of the bilayer to molecules depends on the size of the molecules and its solubility in lipids
-impermeable to ions and large polar molecules such as sugars and AA
-permeable to small non polar molecules such as oxygen and fatty acids
-permeable to small polar molecules such as water and CO2
selectively permeable
-protein channels in the membrane allow the cell to have control over the large polar molecules that may be needed in the cell
-intrinsic proteins, one side of the membrane to the other
communication
-extrinsic proteins allow cells to communicate with one another
-through receptors
-additional carbohydrate groups and become glycoproteins
-allows cells to recognise each other and form tissues
recognition
-some lipids have an extra carbohydrate group and become glycolipids
-extend from surface of the cell and acts as a cell surface receptors for certain molecules
-allow cells to adhere to form tissues
-allows the body to recognise self and non self
simple diffusion
-passive movement of small, non polar lipid soluble molecules such as carbon dioxide from an area of high concentration to an area of low concentration
-molecules move directly through phospholipid bilayer
factors affecting the rate of simple diffusion
-concentration of particles
-distance needed to travel
-surface area
channel proteins
-intrinsic channel proteins
-ions as they are small channels
-span the membrane forming pores that the particles can travel down
-specific
aquaporins
-found on most cell membranes
-allows water to travel through the membrane
-6 alpha helixes which can span the membrane
carrier proteins
-larger molecules need to be carried across the membrane
-when a molecule attaches to the carrier protein it causes a conformational change in the shape to the protein
-this releases the molecule on the other side of the membrane
-specific
factors affecting rate of facilitated diffusion
-concentration
-number of carrier proteins and channels in the membrane
osmosis
-passage of water from an area of high WP to an area of lower WP through a partially permeable membrane
-represented by Psi (pressure created by water molecules)
hypotonic
- 0KPa
-pure water
-red blood cells burst
hypertonic
- -1000KPa
-concentrated solution
-red blood cell shrinks
isotonic
-turgid
-flaccid
-plasmolysed
guard cells
-K ion channels open and K ins move into guard cells
-WP decreases and water moves into the cell by osmosis
-guard cell swells and becomes turgid
-this opens the stoma
factors affecting the rate of osmosis
-water potential gradient
-surface area
-temperature
-the presence of aquaporins
active transport
-low to high concentration
-uses energy in the form of ATP
-uses carrier proteins
process of active transport
-molecule binds to carrier protein
-ATP binds to protein on the inside of the membrane
-ATP hydrolysed to transfer energy, carrier protein changes shape
-molecule release on the other side and carrier protein reverts to original shape
co transport
-indirect or secondary transport
-energy doesn’t directly come from ATP
-ions travelling down their concentration gradient provide the energy
process of co transport
-active transport builds up the concentration gradient
-co transporter (symporter) transports molecules across the membrane in the same direction
-uses energy from active transport
