UNIT 1 - membrane proteins Flashcards
what is the fluid mosaic model?
The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components - including phospholipids, peripheral/integral proteins and carbohydrates - that gives the membrane a fluid character.
what is the function of hydrophobic interactions in r groups and what is the purpose of the interactions?
Regions of hydrophobic R groups allow extensive hydrophobic interactions that hold integral proteins within the phospholipid bilayer.
what are some integral membrane proteins called?
Some integral membrane proteins are transmembrane proteins, which span across the membrane
what do peripheral membrane proteins have on their surface?
Peripheral membrane proteins have hydrophilic R groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions.
what do peripheral membrane proteins interact with?
Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.
what is the phospholipid bilayer?
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules,
how can small molecules pass through the phospholipid bilayer?
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion.
what is facilitated diffusion?
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins.
what allows cell types to preform specialised functions?
to perform specialised functions, different cell types have different channel and transporter proteins.
what are channels?
Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane. Some channel proteins are gated and change conformation to allow or prevent diffusion.
how do ligand-gated channels work?
Ligand-gated channels are transmembrane protein channels that are controlled by the binding of signal molecules.
Ligand-gated channels have a ligand specific to a signal molecule/ligand. The channels open when the ligand is bound and open or close in response to changes in membrane potential.
what is the function of a transporter protein?
Transporter proteins bind to the specific solute to be transported and undergo a conformational change to transfer the substance across the membrane.
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 when transferring substances across a membrane?
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
what protein controls active transport?
transporter proteins are pumps that mediate active transport along with a source of metabolic energy is required for active transport.
how is the electrochemical gradient formed?
the concentration gradient and the electrical potential difference. the electrochemical gradient determines the transport of the solute.
function of ATP/ATPase in active transport?
Some active transport proteins are ATPases which hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane.
when/how is the membrane potential created?
A membrane potential (an electrical potential difference) is created when there is a difference in the electrical charge on the two sides of the membrane.
where do ion pumps receive their energy from?
Ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients.
what is an example of an ion pump?
the sodium-potassium pump
how does the sodium potassium pump work?
- 3 sodium ions bind to the pump.
- pump is phosphorylated due to splitting ATP and changes confirmation meaning that the pump now has a low affinity of sodium
- sodium ions released outside the cell and 2 potassium ions bind to pump
- pump is dephosphorylated and changes conformation and the pump now has a low affinity for potassium ions
- two potassium released inside the cell
which type of cell is the sodium potassium pump found in?
The sodium-potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms.
what does the glucose symport do?
The glucose symport is an integral membrane protein involved in the transport of glucose and sodium ions (high concentration) across it at the same time, and in the same direction:
sodium ions enter the cell down their concentration gradient through diffusion while the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient (active transport)
what is an electrochemical gradient?
a gradient of electrochemical potential. it is formed by the difference in solute concentration and the difference in charge across a membrane. `this is usually for an ion that can move across a membrane,
what are integral membrane proteins?
also called intrinsic proteins; they have one or more segments that are embedded in the phospholipid bilayer
what are peripheral membrane proteins?
membrane proteins that adhere only temporarily to either side of a membrane with which they are associated
what is sodium-potassium ATPase?
the enzyme that acts as the sodium-potassium pump, removing three sodium ions from the cell and taking two potassium ions into the cell during a cycle of action
what is a transporter protein?
a membrane protein involved in the movement of ions, small molecules, and macromolecules (such as another protein) across a membrane. requires energy.
what are voltage gated channels?
a class of transmembrane proteins that form ion channels; they are activated by changes in ion concentration/membrane potential
what are gated channels?
channel-forming proteins controlled by signalling molecules or ion concentration
how are membrane proteins useful in facilitated diffusion?
they act as channels/transporters
describe how an ATPase transporter protein works?
- Hydrolyses ATP directly to produce energy energy for conformational change.
- ATP is dephosphorylated by transporter protein and energy is released to move substances against the gradient
what happens per ATP molecule hydrolysed in the sodium-potassium pump?
For each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell, establishing both concentration and electrical gradients.
what provides energy for the sodium-potassium pump and what does it do?
The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis to actively transport sodium ions out of the cell and potassium ions into the cell.
qualities of a transporter protein?
- uses active transport
- uses energy
- makes the protein undergo a conformational change (never fully open)
what are the two types of channel proteins?
there are two types - permanently open (diffusion) gated channel proteins that open and close (signal molecules or changes in membrane potential)
what do channel proteins not require?
energy
why is the Na/K pump essential for the glucose symport?
as it provides a concentration gradient.
what is required for active transport pumps to function?
- pump
- source of metabolic energy
