B2.1 Membranes and Membrane Transport
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Phospholipids are amphipathic. Explain what this means
they have a hydrophilic head and and hydrophobic tail
Name another amphipathic lipid
cholesterol
what happens when phospholipids are placed in water
the hydrophilic phosphate heads orient towards the water and hydrophobic hydrophobic tails orient away from the water forming a PHOSPHOLIPID MONOLAYER
what are the 2 regions of a phospholipid bilayer
a hydrophobic core and a hydrophilic outer layer
what cannot pass through the hydrophobic region of the lipid bilayer barrier and why
• large molecules because the hydrophobic region is tightly packed and has low permeability for them -polar molecules and ions as they are hydrophilic so will not interact
integral proteins
partially hydrophobic and embedded in phospholipid bilayer
peripheral proteins
hydrophilic and are attached to surface of integral proteins or to membrane with a a hydrocarbon chain
2 types of transport proteins
channel and carrier
what are channel proteins
form holes or pores where molecules travel through eg ions some are gated
what do carrier proteins do
change shape to transport substance across the membrane
glycoproteins
act as cell markers/antigens for cell to cell recognition
what is simple diffusion
the net movement, due to random motion of molecules or ions, of a substance from a region of higher concentration to a region of lower concentration
molecules that move by simple diffusion
oxygen- diffuses into cells from capillaries surrounding- conc gradient by respiration carbon dioxide- diffuses out of cells into surrounding capillaries
what does the rate of diffusion depend on
steepness of conc gradient temperature surface area properties of molecules or ions
the higher the difference in conc across membrane…
higher the rate of diffusion
the higher the temperature
the higher the rate of diffusion because molecules have more kinetic energy so random movement of molecules is faster
the greater the surface area
the higher the rate of diffusion
the larger the molecule
the slower it diffuses because they require more energy to move
what can diffuse quickly
uncharged molecules - oxygen- as they can move directly across phospholipid bilayer non polar molecules because they are soluble in the bilayer smaller polar molecules- urea
what is osmosis
the diffusion of water molecules from a region of lower solute concentration to a region of higher solute concentration, across a partially permeable membrane
what channel proteins allow water to pass through membrane easily
aquaporins
when does facilitated diffusion occur
when substances cross phospholipid bilayer with the help of channel and carrier proteins- passive and down a con gradient
how does a carrier protein work
the substance that needs transporting attaches to binding site and the shape of the protein changes so it opens up to the other side of the membrane
what is active transport
the movement of molecules and ions across a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration