1.3 membrane proteins Flashcards
what is the plasma membrane made up of, illustrated by the fluid mosaic model?
phospholipids, cholesterol, proteins and carbohydrates
which r groups do peripheral proteins contain?
hydrophilic
which type of r group is found in integral proteins?
hydrophobic
why do peripheral proteins have hydrophilic r groups?
to allow them to bind to the surface if the membrane
why do integral proteins have hydrophobic r groups?
to allow for strong hydrophobic interactions that allow the protein to be held within the phospholipid bilayer
how does the phospholipid bilayer act as a barrier to ions and most polar molecules?
due to its hydrophobic nature
what is the role of transmembrane proteins?
to act as channels/transporters and allow passive transport of substances to take place via facilitated diffusion
what are gated channels?
channels that change conformation to allow or prevent diffusion
how do gated channels open/close?
by responding to stimuli
how are ligand-gated channels controlled?
by the binding of signal molecules
how are voltage-gated channels controlled?
by changes in concentrations
how do transporter proteins transport solutes?
the protein binds to a substance that is to be transported and undergoes a conformational change that allows the transfer of the solute across the membrane
why do transporter proteins alternate between two conformations?
so that the binding site for the solute is exposed to one side of the bilayer, then the next
what happens when transporter proteins require energy to bring about conformational change?
the transport becomes active, using energy from the hydrolysis of ATP
what is membrane potential?
the electrical potential difference created when there is a difference in electrical charge on the two sides of the membrane
what is the electrochemical gradient?
when concentration gradient and membrane potential combine
does the electrochemical gradient determine?
the transport of the solute
which way does the SPP transport sodium ions?
out of the cell
which way does the SPP transport potassium ions?
into the cell
what is step 1 in the workings of the SPP?
the transporter protein has a high affinity for sodium ions, therefore binding occurs.
what is step 2 in the SPP?
phosphorylation by ATP causes the conformation of the protein to change
what is step 3 in the SPP?
the affinity for ions decreases resulting in sodium being released from the cell
what is step 4 in the SPP?
potassium ions from outside of the cell bind to the sodium/potassium pump
what is step 5 in the SPP?
dephosphorylation occurs which causes the conformation of the protein to change
what is step 6 in the SPP?
potassium ions are taken into the cell and affinity returns to the start
explain the net charge produced by the SPP
for every 3 Na ions pumped out, only 2 K ions are pumped in. This creates a slightly -ve charge in the cell
what is the main function of the SPP?
generation of the sodium ion gradient across the PM for the active transport of glucose in the small intestine (epithelial cells)
what does the glucose transporter transport?
both sodium and glucose at the same time and direction
describe the concentration gradients involved with the glucose transporter
sodium ions enter down their concentration gradient while glucose goes against its concentration gradient
