membranes Flashcards
what does amphipathic mean
consists of both hydrophilic and hydrophobic regions
what are cellular membranes formed from
phospholipid bilayers, polar hydrophilic head facing outwards and hydrophobic tails facing inside
name the 3 major membrane lipids
glycerophospholipids, sphingolipids, sterols
what are glycerophospholipids and describe their structure
-phosphorylated head group, glycerol, 2 hydrocarbon fatty acid chain
-amphipathic
-fatty acid can be saturated or unsaturated
what are sphingolipids and describe their structure
-phosphorylated head group, sphingosine backbone, 2 hydrocarbon fatty acid chains
-amphipathic
what are sterols and describe their structure
-cholesterol in animals
-influences membrane fluidity/rigidity
-unsaturated, double bonds in fatty acid tails provide space for sterols to sit in membrane
why have a selectively permeable barrier
maintain pH and ionic composition, regulate cell volume, generate ion gradient (muscles and nerve cells)
functions of channels/transporters/pores
allows compounds to enter/exit cell either along conc gradient (passively) or by using energy to go against conc gradient (active transport)
what do receptors and adhesion molecules do
bind extracellular molecules so other cells can sense them
name types of membrane proteins
channels, pores, transporters, receptors, adhesion molecules, enzymes
what molecules can pass through the membrane unaided and what cant
water, gases, urea can pass through bilayer unaided
-water needs facilitated transport by aqua porins, gases diffuse
ions, sugars, amino acids cannot pass through unaided
-need channels/transporters
what is diffusion rate influenced by
-concentration gradient steepness
-temperature
-surface area
-diffusion distance
-size/mass of substance
transport by diffusion is driven by differences on either side of the membrane, what are the differences that drive diffusion
chemical, electrical
examples of transporters
uni/sym/antiporters, ATP-binding cassette
what are gap junctions
channels that connect directly with neighbouring cells, allows rapid movement of ions
describe gated ion channels and give examples of each
highly specific for specific ions, open and close in response to a particular signal
ligand gated-acetyl choline
voltage gated- potential differences/depolarisation
what do transporters do
move compounds in and out of cell against their concentration gradients
-requires energy supplied by ATP hydrolysis
what supplies energy for active transport
ATP hydrolysis
what are symporters
cotransporters that transfer both molecules in the same direction
what are antiporters
cotransporters that transfer molecules in opposite directions (one goes in membrane and one goes out)
what does ABC transporter stand for
ATP binding cassette
what do receptors do
detect extracellular signals called ligands like hormones
how does secondary active transport/cotransport work
movement of a molecule down a conc gradient along with other ions like glucose, moves a molecule along its concentration gradient using energy indirectly to make a proton/sodium gradient
what is pinocytosis
continuous process involving the uptake of extra cellular fluid via small membrane vesicles
what are agonists and give an example
stimulate receptors, activate target as a ligand eg. insulin
what are antagonists and give an example
inhibitors, blocks activation of target eg. beta blockers blocking adrenaline receptors
function of transporters
move compounds in and out of cell against their conc gradient
function of channels/pores
allow compounds to enter/leave along their conc gradient
function of receptors
bind to extracellular molecules and convey signals across/into the cell
function of adhesion molecules
allow cells to sense their environment, stick together to form tissues and adhere to extracellular matric
name membrane proteins
transporters, channels, pores, receptors, enzymes, adhesion molecules
what is active transport
transport of a molecule against its concentration gradient
what is passive transport
-doesnt require input of metabolic energy
-driven by conc gradient
what is exocytosis
secretion of proteins out and across the cytoplasmic membrane
what is endocytosis
uptake of macromolecules from extracellular space across cytoplasmic membrane
name the types of endocytosis
-receptor mediated endocytosis
-phagocytosis
-pinocytosis
what is the process of exocytosis
- protein packaged into secretory vesicles by golgi and targeted to membrane
- vesicles fuse with membrane and release contents extracellularly
what is the process of endocytosis
small portion of membrane envelopes molecule and pinches off to form a intracellular vesicle
-involves clathrin coated pits and vesicles
what is clathrin
protein with 3 legged structure called triskelion which assembles into a basket structure
what is phagocytosis
specialised from of endocytosis in macrophages and neutrophils to ingest bacteria and cell debri
why cant bacteria do endocytosis/exocytosis and what do they do instead
they have dedicated transporter systems called translocases and the cell wall doesnt allow exo/endocytosis
what are translocases
dedicated transporter systems in bacteria
