B5 - plasma membranes Flashcards
Define osmosis (2)
net movement of water from a high to low water potential trough a partially permeable membrane
Define active transport. (2)
Movement of ions from a low to high concentration, against the concentration gradient.
Active as requires energy from ATP
Define diffusion
PASSIVE movement of particles from a high to low concentration, down a concentration gradient.
Explain the mechanism of active transport. (4)
- molecule binds to receptor on carrier protein (outside the cell)
- ATP binds to carrier inside cell
- ATP hydrolysed into ADP + Pi
- phosphate stays bound to carrier protein, causing it to change shape and open to the inside of the cell
- Phosphate released & recombines with ADP to form ATP
- carrier returns to original shape
what is hydrostatic pressure?
osmosis in a closed tissue.
Why is the plasma membrane ‘partially permeable’?
Hydrophobic core repels ions, but small polar ions can pass through
Effect of osmosis in plant cells (hyper and hypotonic)
in hypertonic solution:
- water moves out cell
- plasmolysis = reduces cytoplasm volume, pulling the plasma membrane away from the cell wall.
In hypotonic solution:
- water moves in cell
- increase hydrostatic pressure
- cell becomes turgid
- doesn’t burst due to cell wall
Effect of osmosis in animal cells (hyper & hypotonic)
In hypertonic solution:
- water leaves cell
- crenation
- cell shrinks/shrivels
In hypotonic solution:
-water moves in
- increase hydrostatic pressure
- cell swells & bursts
- lysis
What is the role of the cell membrane on the surface/ outside cell?
- allows transport in & out cells
- separate cell content from environment
- permits transport by exo&endocytosis
- made of fat = barrier to water soluble molecules
- permeable to small molecules (e.g. H2O, CO2, O2)
- CELL RECOGNITION: e.g. in immune response
- CELL SIGNALLING: provides receptors for signalling molecules
What is the role of membranes inside the cell?
- separate DNA
- COMPARTMENTALISATION: separate organelles so independent reactions can occur independent of one another
- surrounds most organelles (NOT RIBOSOMES OR CENTRIOLES)
- provide large SA for attachment of enzymes/pigment molecules e.g. chlorophyll
- surrounds vesicles (transport proteins from RER to golgi)
-selectively permeability of organelles - isolate harmful enzymes in lysosomes
What is the ‘fluid mosaic’ model?
FLUID = phospholipids & proteins embedded are free to move independent of each other
MOSAIC = embedded proteins vary in shape, size & position
What is the structure of the phospholipid bilayer?
- hydrophilic phosphate heads on outside towards aq environment, protecting hydrophobic fatty acids on inside
- hydrophobic core
What are intrinsic proteins? Give examples
Span whole width of membrane
- have hydrophobic R-groups that react with hydrophobic core of membrane
CHANNEL:
- passive
- hydrophilic channel
- gated
CARRIER:
- passive & active
- molecule attach to binding site
- undergoes conformational shape change
- opens to other side of membrane
What are glycoproteins?
Intrinsic proteins
- attached carbohydrate chain
- important in cell signalling
- important in cell adhesion
Act as a receptor for:
- hormones e.g. insulin
- neurotransmitters at synapses
- transport (protein movement)
Define cell signalling.
When a chemical binds to a receptor and elicits a response which sets of a cascade of events in the cell.
