transport across cell membranes Flashcards
what is the structure of a cell surface membrane
draw
phospholipid
channel protein
carrier protein
glycolipid
glycoprotein
what do the component of the cell surface membrane do
phospholipid bilayer
- allows diffusion of lipid soluble (non polar) substances and very small molecules
- restricts movement of water soluble (polar) substances and larger molecules
channel proteins
- allow the diffusion of water soluble substances (facilitated diffusion)
carrier proteins
- allow diffusion or slightly la her substances (facilitated diffusion)
- allow active transport of substances against concentration gradient
cholesterol
- restricts movement of other molecules decreasing fluidity
glycoproteins
- act as receptors involves in cell signalling
glycolipids
- act as antigens for cell recognition
what are the adaptations of cells for transport across their internal or external membranes
membrane folded eg. microvilli in ileum to increase surface area
more protein channels/carriers for facilitated diffusion
what is simple diffusion
net movement of lipid soluble/non polar or very small substances
form an area of higher concentration to an area of lower concentration down a concentration gradient
across the phospholipid bilayer
what are the factors affecting simple diffusion
conc. gradient
surface area of membrane
temperature
what is facilitated diffusion
net movement of water soluble/polar or slightly larger substances down a conc. gradient
through channel and carrier proteins
which are complementary to a substance- shape and charge of channel determines which substances move
what are the factors affecting facilitated diffusion
conc. gradient (until number of proteins in a limiting factor)
number of channel and carrier proteins
surface area of membrane
what is the role of a channel protein
water soluble substances
pore filled with water
may be gated - can open or close
what is the role of a carrier protein
slightly larger substances
complementary substance attaches to binding site
protein changes shape
substance released on side of lower conc.
what is osmosis
net diffusion of water
from an area of high to low water potential
down a water potential gradient through a partially permeable membrane
what are the factors affecting rate of osmosis
surface area of membrane
water potential gradient
what is water potential
pressure exerted by water molecules on a membrane measured in KPa
a measure of how likely they are to move out of the solution
increasing solute concentration decreases water potential
more negative = high solute conc.
less negative = dilute solute conc.
what is the effect on animal and plant cells if the water potential of the solution is lower than cells
general effect - water moves out of cell by osmosis
effect on plant cells - shrink, become flaccid/plasmolysed
effect on animal cells - shrink, become crenated
what is the effect on animal and plant cells if the water potential of the solution is same than cells
general effect - no net movement of water
plant cells - no change
animal cells - no change
what is the effect on animal and plant cells if the water potential of the solution is higher than cells
general - water moves into cells by osmosis
plant - swell, turgid
animal - swell, may burst
what is a hypertonic solution
lower water potential than cells
cells shrivel
what is a isotonic solution
same water potential as cells
what is a hypotonic solution
higher water potential than cells
cells burst
what is active transport
movement of substances from an area of lower to higher concentration (against a concentration gradient)
requires the hydrolysis of ATP and a specific carrier protein
what are the factors affecting active transport
pH / temperature (tertiary structure of carrier protein)
number of carrier proteins
rate of respiration (ATP production)
what is the process of active transport
- complementary substance binds to a specific carrier protein
- ATP binds and is hydrolysed into ADP + Pi releasing energy
- this causes the carrier protein to change shape releasing substance in side or higher conc.
- Pi released and protein returns to original shape
what is co-transport
movement of two substances simultaneously via co- transport protein
movement of one substance is against conc. gradient is coupled with the movement of another down conc. gradient
what is the process of co transport
- Na+ actively transported from epithelial cells to blood by sodium potassium pump
- this establishes a conc. gradient of Na+
- Na+ enters epithelial cells down its conc. gradient with glucose against its conc. gradient via co transporter protein
- glucose moves down a conc. gradient into blood via facilitated diffusion
