cell membranes and transport Flashcards
what type of molecule does the phospholipid component let across the membrane
lipid soluble and not water soluble
what characteristics does a phospholipid molecule have
they can form bilayers - one sheet opposite the other
hydrophillic heads on the inner and outer layers to interact with water in the cytoplasm and outside the cell hydrophobic heads facing inside of cell
what are intrinsic proteins
they extend across both surfaces of the bilayers and include transport proteins which use active or passive transport to move molecules or ions across the membrane
what do extrinsic proteins do
provide structural support and form recognition sites by identifying cells and receptor sites for hormone attatchment
where are extrinsic proteins found
on either surface of the bilayer
where does cholesterol occur in membranes and what is the function
in between the phospholipid molecules
makes the membrane more stable at higher temperatures and more fluid at lower temperatures
what is the glycocalyx
the carbohydrate molecule around an animal cell
some cells form hormone receptors or in cell to cell adhesion
how does the glycocalyx form
when the extracellular proteins are glycosylated
why is the model called fluid mosaic
individual proteins can move relative to their layers (fluid )
embedded proteins in the bilayer vary in shape size and in their distribution between the phospholipids
how do small molecules like o2 get across the membrane
they move between the phospholipid molecules and diffuse across the membrane
how do lipid soluble molecules get across the membrane e.g vitamin a
they dissolve in the phospholipid and diffuse across the membrane
how do water soluble molecules e.g glucose get across the membrane
they cant diffuse so they have to pass though the intrinsic protein molecules which form water filled channels across the membrane so it is selectively permeable to water and some solutes
what factors affect the rate of diffusion
concentration gradient
thickness of exchange surface or distance of travel
surface area of membrane
temperature
size of diffusing molecules
what is simple diffusion
the passive movement of a molecule or ion down a concentration gradient from a region of high to low concentration
what is facilitated diffusion
passive transfer of molecules/ions down a concentration gradient across a membrane by channel or carrier protein molecules in the membrane
what are carrier proteins used for
diffusion of larger molecules e.g sugars and amino acids
what are channel proteins
molecules with pores lined with polar groups/ hydrophillic ions so that water soluble molecules can pass through
when do channel proteins open and close
according to the cells needs
how do carrier proteins transport molecules
a molecule attatches to binding site on the carrier protein which changes shape and releases molecule on the other side of the membrane
what are the differences between carrier and channel proteins
carrier proteins are slower transport
channel proteins only transport water soluble , carrier proteins transport soluble and insoluble molecules
carrier proteins also allow active transport
what is osmosis
net passive diffusion from of water molecules across a selectively permeable membrane from a region of high water potential to a region of low water potential
what is water potential
the measure of free energy of water molecules and the tendency for water to move
what does solute potential measure
how easily water molecules move out of a solution
how does solute potential work
the more solute , the more tightly the water molecules are held so lower tendency of water to move out of solution
higher conc solution= more negative solute potential
what is pressure potential
hydrostatic pressure exerted by the cell contents on the cell wall
equal and opposite to pressure exerted by cell wall on cell contents
how do you work out the water potential
pressure potential + solute potential
what is an isotonic solution
when the WP is the same in external solution and solution inside of cell
no net movement of water
What is a hypertonic solution
when the external solution has a lower WP than the solution inside the cell
water flows out of the cell
what is a hypotonic solution
when the WP is higher in the external solution than the WP of the solution inside of the cell
water flows into the cell
what type of solution does plasmolysis occur in
hypertonic
what is plasmolysis
retraction of cytoplasm and cell membrane from the cell wall as the cell loses water through osmosis
cell becomes flaccid and floppy
What processes use active transport
muscle contraction
Mineral uptake into plant root hairs
Nerve impulse transmission
How does active transport occur
Through intrinsic carrier proteins spanning the membrane
What is active transport
movement of molecules or ions across a membrane against concentration gradient using energy from the hydrolysis of ATP
What happens when the cell is turgid
the cytoplasm is pushed against the cell wall
What happens when the cell is at incipient plasmolysis
Cytoplasm is beginning to pull away from the cell wall
What happens when the cell is plasmolysed
Cytoplasm is completely pulled away from the cell wall
How is haemolysis caused
when a RBC is put into pure water water enters through osmosis and it bursts
How is crenation of a red blood cell caused
when its put into a hypertonic solution and all water leaves through osmosis
what is exocytosis
the active process of the cell membrane engulfing material bringing it into the cell in a vesicle
what is endocytosis
the active process of the cell membrane engulfing material bringing it into the cell in a vesicle
what is phagocytosis
the active process of of the cell membrane engulfing large particles bringing them into the cell in a vessicle
what is pinocytosis
the active process of the cell membrane engulfing droplets of fluid bringing them into the cell in a vesicle
