Membrane proteins Flashcards
What is the fluid mosaic model of cell membranes?
The fluid mosaic model explains various observations regarding the structure of functional cell membranes. According to this biological model, there is a lipid bilayer in which protein molecules are embedded. The lipid bilayer gives fluidity and elasticity to the membrane.
What are integral proteins and how they held in place?
Integral - positioned with a section within the hydrophobic region of the membrane. Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer. Integral membrane proteins interact extensively with the hydrophobic region of membrane phospholipids. This is the main difference between integral and peripheral proteins.
What are the features of peripheral proteins?
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. Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.
Which substances can pass through the phospholipid bilayer by simple diffusion?
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion.
Which substances cannot pass through the phospholipid bilayer by simple diffusion?
Large polar molecules, ions, charged polar molecules
What is facilitated diffusion? Give an example.
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins. To perform specialised functions, different cell types have different channel and transporter proteins. Potassium ion channel.
What is the structure of channel proteins?
A channel protein is a special arrangement of amino acids which embeds in the cell membrane, providing a hydrophilic passageway for water and small, polar ions.
How do ligand-gated channels function? Give an example.
Ligand gated channel proteins - allow passage of solutes by altering the conformation
How do transporter proteins function? Give an example.
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute 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 is an example of a transporter protein (pump) that requires an energy source?
Sodium Potassium ATPase “Pump”
What is a symport? Give an example of a symport and detail the process of ion movement in a symport.
A symporter is an integral transporter membrane protein that is capable of transporting 2 or more different molecules at the same time, in the same direction.
Example - Glucose Symport. In the small intestine, the sodium gradient created by the sodium-potassium pump drives the active transport of glucose.
In intestinal epithelial cells the sodium potassium pump generates a sodium ion gradient across the plasma membrane.
Glucose co-transports with sodium.
When the glucose and the Na+ bind to the symport there is a conformational change that allows for the transport of the glucose against the concentration gradient.
This does not directly require energy. The Na+ ions must be actively pumped out of the cell for this to occur.
