transport across membrane Flashcards
what are the 4 components of the membrane?
phospholipids, cholesterol, proteins and carbohydrates
why are cell membranes fluid/can move about?
phospholipid molecules in the membrane are held together primarily by weak hydrophobic interactions
how do phospholipid molecules move about the membrane?
phospholipid molecules can move about laterally across the membrane, rotate and very RARELY flip transversely
how does temperature affect membrane fluidity?
as temperature increases, membrane fluidity increases
increased k.e. = increased lateral mvmts = overcome hydrophobic interactions = increased space to move = more fluid
how does length of fatty acid chain affect membrane fluidity?
as length of fatty acid chain increases, membrane fluidity decreases
longer hydrocarbon chain = more hydrophobic interactions = more rigid membrane = less fluid
how does degree of saturation of fatty acids affect membrane fluidity?
as degree of saturation increases, membrane fluidity decreases
saturated lipids = long, straight hydrocarbon chains = close packing + more hydrophobic interactions = less fluid
how does cholesterol affect membrane stability?
the rigid steroid ring of cholesterol interferes with the motions of the hydrocarbon chains, enhancing mechanical stability
how does cholesterol affect membrane fluidity?
cholesterol has dual effects on membrane fluidity.
high temp: restrains movements of phospholipids by interfering with the motions of hydrocarbon chains
low temp: prevents hydrocarbon chains from packing closely together
how does the presence of cholesterol affect membrane permeability?
cholesterol decreases the permeability by filling in spaces/plugging transient gaps between hydrocarbon chains in phospholipids
ATESCI
what are the 6 functions of membrane proteins?
anchorage
transport
enzymatic activity
signal transduction
cell-to-cell recognition
intercellular joining
what are the functions of carbohydrates in the membrane?
- sorting cells
- binding extracellular signal molecules
- intercellular adhesion
- cell-to-cell recognition
what are the 2 types of transport proteins?
channel proteins and carrier proteins
is ATP needed for facilitated diffusion?
no
what substances are transported by facilitated diffusion?
larger, hydrophilic substances
ASSTCD
what are the 6 factors affecting the rate of diffusion?
area across which diffusion occurs
structure through which diffusion occurs
size and type of diffusing molecule
temperature
concentration gradient
distance across which diffusion occurs
what does ‘less negative’ water potential mean?
higher water potential
what is the sign for solute potential (+ve/-ve)
solute potential is ALWAYS NEGATIVE
pressure potential is always positive
what happens when a plant cell is placed in solutions of different water potentials?
less negative water potential -> turgid
same water potential -> no change
more negative water potential -> plasmolysed
what happens when an animal cell is placed in solutions of different water potentials?
less negative water potential -> swells & lyses
same water potential -> no change
more negative water potential -> shrivelled
how is a solute actively transported across a membrane via a carrier protein?
- solutes on the cytoplasmic side bind to a specific binding site on the transport protein
- ATP transfers a phosphate group to the transport protein
- this causes the protein to change its conformation such that the solute is released on the other side of the membrane
- the phosphate group detaches and the transport protein returns to its original state
what is endocytosis?
the cell TAKES IN macromolecules by invagination
what is exocytosis?
the cell SECRETES macromolecules by fusion of vesicles
what are the 3 types of endocytosis?
phagocytosis
pinocytosis
receptor-mediated endocytosis
what are the key functions of the cell membrane?
- definition of cell’s boundaries
- organisation & location of function
- regulation of cell’s contents
- signal transduction
- cell-to-cell communication
