1.3 Membrane Proteins Flashcards
what do regions of hydrophobic R groups allow
strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer
what are the different types of membrane proteins
integral and peripheral
what do integral membrane proteins interact with
they interact intensively with the hydrophobic region of membrane phospholipids
what are integral proteins
transmembrane proteins
what do peripheral membrane proteins have
hydrophilic R groups on their surface and are bound to the surface of membranes, by ionic and hydrogen bond interactions
what do peripheral membrane proteins interact with
they interact with the surface of integral membrane proteins
what is the phospholipid bilayer
a barrier to ions and most uncharged polar molecules
how do small molecules pass through the bilayer
small molecules such as oxygen and carbon dioxide pass through the bilayer by simple diffusion
what is facilitated diffusion
the passive transport of substances across the membrane through specific transmembrane proteins
what do cells have to perform specialised functions
different cell types have different channels and transporter proteins
most channel proteins in animal and plant cells are
highly selective
what are channels
multi-subunit proteins with the subunit arranged to form water-filled pores that extend across the membrane
what do channels have to prevent diffusion
some channel proteins are gated and change conformation
what are the different types of channel protiens
ligand-gated
voltage-gated
what are ligand-gated channels controlled by
the binding of signal molecules
what are voltage-gated channels controlled by
changes in ion concentration
what are the different types of proteins involved in transporting substances
channel proteins (facilitated diffusion (passive)) transporter proteins (facilitated diffusion (passive)) protein pumps
why do transporter proteins bind to the specific substance
to be transported and undergo a conformational change to transfer the solute across the membrane
why do transporters alternate between two conformations
so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other
what does active transport use
pump proteins that transfer substances across the membrane against their concentration gradient
pumps that mediate active transport are
transporter proteins coupled to an energy source
what is required for active transport
a source of metabolic energy
why do some active transport proteins hydrolyse ATP directly
to provide the energy for the conformational change required to move substances across the membrane
what hydrolyses ATP
ATPases
what determines the transport of the solute for a solute carrying a net charge
the concentration gradient and the electrical potential difference combine to form the electrochemical gradient that determines the transport of the solute
how is a membrane potential created
(an electrical potential difference) when there is a difference in electrical charge on the two sides of the membrane
what do ion pumps use energy for
ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients
how does the sodium-potassium pump transport ions
transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
what does a sodium-potassium pump transport
actively transport sodium ions out of the cell and potassium ions into the cell
what are the stages that the sodium-potassium pump goes through
high affinity for sodium ions inside the cell binding occurs phosphorylation by ATP conformation changes affinity for sodium decreases sodium ions released outside of the cell potassium ions bind outside of the cell dephosphorylation conformation changes potassium ions taken into cell affinity returns to start
how many ions are transported through the cell membrane
for each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell.
this establishes both concentration gradients and an electrical gradient
why is the sodium-potassium pump important
it is found in most animal cells and accounts for a high proportion of the basal metabolic rate in many organisms
what does the sodium gradient in the small intestine lead to
the sodium gradient created by the sodium-potassium pump drives the active transport of glucose
what happens with the sodium-potassium pump in intestinal epithelial cells
the sodium-potassium pump generates a sodium ion gradient across the plasma membrane
what is the glucose transporter responsible for
the glucose symport transports sodium ions and glucose at the same time and in the same direction
how are sodium ions and glucose transported in the concentration gradient
sodium ions enter the cell down their concentration gradient, the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient
