plasma membranes Flashcards
how are the phospholipids positioned in the phospholipid bilayer
the hydrophilic phosphate heads face outwards and sandwich the hydrophobic fatty acid tails to make a hydrophobic centreb
what is the fluid mosaic model
proteins occupy various spaces in the membrane, the phospholipids are free to move within the layer relative to each other giving the membrane flexibility, and because the proteins vary in shape size and position (like a mosaic)
what are intrinsic proteins
transmembrane proteins embedded through both layers of a membrane, their hydrophobic r groups on their external surfaces interact with the hydrophobic core keeping them in place
describe channel proteins
provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient, held in place by hydrophobic interactions between core of the membrane and the hydrophobic r groups on outside surface of proteins
describe carrier proteins
have an important role in both passive and active transport, often involves the shape of the protein changing
what are glycoproteins
embedded in the cell surface membrane with attached carbohydrate chains, play a role in cell adhesion to form certain tissues, and as receptors for chemical signals
what do glycolysis do
lipids with attached carbohydrate chains, cell markers for the rest of the immune system as self or non self
what are extrinsic proteins
are present in one side of the bilayer, can be present in either layer and some move between the two
what does cholesterol do
regulates fluidity of membranes, positioned between phospholipids in a membrane bilayer, its hydrophilic end interacting with the heads and its hydrophobic end interacting with the tails pulling them together but prevent membrane become too solid by stopping phospholipid molecules from grouping too closely
how does temperature affect the membrane
increased temperature gives the phospholipids more kinetic energy, so will move more, increasing permeability, eventually membrane will start to break down, transport proteins denature
what will organic solvents do to membranes
dissolve the membrane, disrupting cells, causing disruption to specific functions such as transmission if nerve impulses by neurones
describe the exact process of active transport via a carrier protein
the molecule/ion to be transported binds to the receptors of the protein, ATP binds to the inside of the protein and is hydrolysed into ADP and phosphate, binding of the phosphate molecule causes the protein to change shape, opening ups to the inside of the cell and the molecule or ion is released, phosphate molecule released and recombines to form ATP, protein returns to normal shape
what form of transport is bulk transport
active transport
what is endocytosis
the bulk transport of material into cells, two types are phagocytosis (solids) and pinocytosis (liquids). First the membrane bends inwards when it comes into contact with the material. The membrane enfolds the material until eventually the membrane fuses forming a vesicle which moves into the cytoplasm
what is exocytosis
the reverse of endocytosis, vesicles formed by the golgi apparatus, move towards and fuse with the outer surface membrane, contents are then released
