4) Cell membranes and Transport Flashcards
how thin is the cell surface membrane ?
7 nm
what is the phospholipid structure ?
- polar phosphate head (hydrophilic)
- hydrophobic fatty acid (lipid) tails
what does hydrophobic mean ?
no electrical charge, so not attracted to water molecules
what does hydrophilic mean ?
has an electrical charge, and is attracted to water molecules
what is a glycoprotein ?
carbohydrate attached to a protein
difference between placement of integral and peripheral proteins ?
- peripheral : on the edge or outside (do not cross middle line)
- integral : cross the middle line
state the roles of a phosphate head
- stability
- hydrophilic/attracted to water
- attracted to extracellular water/ water in cytoplasm
state the roles of a fatty acid tail
- fluidity = unsaturated
- stability = hydrophobic interactions between tails
- barriers to hydrophilic substances (eg. glucose/ions)
state the roles of cholesterol
- stability between fatty acid tails
- prevents passage between tails
- decreases fluidity
state the roles of glycolipids
- stability (hydrophobic)
- receptor for signal molecule
- cell recognition (can be an antigen)
state the roles of peripheral proteins
- cell recognition/ antigen
- cell adhesion (cells stick together)
- eg: glycoproteins
state the roles of integral proteins
- moves polar substances/ions through membrane
- transport proteins (channel/carrier)
- pumps (active transport)
- membrane bound enzymes
state the roles of glycoproteins
- cell recognition (antigen)
- cell signalling
- receptor for hormones (neurotransmitters)
the main stages of cell signalling
- ligands (cell signalling molecules) are secreted from a cell (the sending cell) into the extracellular space.
- They are then transported through the extracellular space to the target cell.
- The ligands bind to the surface receptors (specific to that ligand) on the target cell. : These receptors are formed from glycolipids & glycoproteins.
- The message carried by the ligand is relayed through a chain of chemical messengers inside the cell = triggering a response.
2 differences between active and passive transport
- Active : uses ATP
: goes against concentration gradient. (low –> high) - Passive : does not use ATP
: goes down the concentration gradient. (high –> low)
What are the 2 types of active transport and also their types?
- Active transport : pumps & carrier
- Bulk transport : endocytosis & exocytosis
what are the 3 types of passive transport?
- Simple diffusion
- Osmosis
- Facilitated diffusion : channel & carrier
what is diffusion ?
net movement of molecules from a region of high concentration to low concentration, using energy from the random movement of particles.
what are some factors affecting diffusion ?
- concentration gradient (greater the diff in concentration between 2 regions, greater amount diffuses)
- distance (shorter the distance, greater the diffusion)
- area (larger the area, greater the diffusion)
- size/type of diffusing molecules (smaller / soluble will diffuse faster)
what can go through the lipid bilayer, and what cannot ?
- can go through : hydrophobic & small uncharged molecules (H20)
- cannot : large uncharged molecules & ions (Na+)
what is facilitated diffusion ?
the transport of polar molecules and ions into and out of a cell. It involves the use of carrier and channel proteins.
state 5 differences between channel & carrier proteins
channel proteins (position fixed)
- transport ions
- soluble molecules diffuse thru the pores
- high transport rates
- do not bind with solute molecules it transports
- only transport water soluble molecules
carrier proteins (flip between 2 conformations)
- transport molecules
- solute molecules bound to one side, released from other side
- low transport rates
- consist of alternative solute-bound conformations
- transport both water soluble and insoluble molecules.
what is osmosis ?
diffusion of water molecules from high water potential to low water potential through a partially permeable mebrane
what is the highest water potential ? (and unit)
0 kPa = water
define hypotonic, isotonic, and hypertonic
- hypotonic : higher water potential than the cell (turgid)
- isotonic : same water potential as cell.
- hypertonic : lower water potential than cell (flaccid/plasmolysed)
state basic stages of active transport
- particle enters the pump
- binds to a specific site
- uses ATP to change shape of pump
- particle released on the side w higher concentration
- pump then returns to its original shape
describe endocytosis
(into cells)
- part of plasma membrane pulled inwards
- a droplet of fluid becomes enclosed when a vesicle is pinched off
- vesicles can then move through the cytoplasm carrying contents
describe exocytosis
(out of cells)
- vesicles FUSE w plasma membrane
- contents of vesicle expelled
- membrane then flattens out again
differentiate between phagocytosis & pinocytosis
- Phagocytosis : bulk uptake of SOLID material + cell EATING.
(eg: engulfing of bacteria by white blood cells) - Pinocytosis : bulk uptake of LIQUID + cell DRINKING.
(eg: absorb nutrients from food)
Summary of differences between passive and active transport
(pg. 16 of 31 from chapter 4 notes )
relationship between surface area and diffusion
greater the surface area, faster the diffusion
describe turgid plant cell
- hypotonic solution
- higher water potential than the cell, so water moves into the cell
- protoplast swells and presses against cell wall
describe plasmolysis (flaccid)
- hypertonic solution
- lower water potential than the cell, so water moves out of the cell
- protoplast pulled away from cell wall
explain why phospholipds are able to form bilayer
- polar hydrophilic phosphate groups on the outside.
- so heads face watery env & tails face away / each other
explain how the structure of phospholipid molecule makes it suitable for its function
- polar hydrophilic phosphate heads face outwards into water.
- alternatively 2 layered structures called bilayers can form in sheets.
- forms hydrogen bond with water & stabilises membrane.
how does inner membrane differ from outer membrane
- fewer channel proteins
- less unsaturated fats
- reduced gaps between membrane molecules
2 similarities between active transport and faciliated diffusion
- both use carrier proteins
- both are specific/ have specific binding site.
