Membrane Proteins Flashcards
Describe the fluid mosaic model of a cell membrane.
A phospholipid bilayer gives the membrane its fluid property as the phospholipids can slide past each other, while integral and peripheral membrane proteins on and in the membrane give it a mosaic like quality.
Describe the structure of a phospholipid in terms of charge and how it forms a membrane.
A hydrophilic (polar, water loving) head dissolves in water while the hydrophobic (non-polar, water hating) tail is repelled by water. The tails cluster inwardly forming a bilayer where only polar heads are exposed to water.
State what is meant by an integral membrane protein and why it is “integral”, give an example.
A protein with hydrophobic R-groups, repelled by water and so firmly embedded in the membrane/bilayer. An example is a channel or transporter protein. Any other relevant example.
What is the term used to describe integral membrane proteins that span the entire width of the membrane?
Transmembrane proteins.
What is meant by a peripheral membrane protein and why is it “peripheral”?
Peripheral membrane proteins have hydrophilic R groups on their surface and are loosely bound
to the surface of membranes, mainly by ionic and hydrogen bond interactions, they are free to move around. Many peripheral membrane proteins interact with the surfaces of integral membrane
proteins.
Why is the phospholipid bilayer a barrier to some mollecules but not others?
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules becuase they may be too big to fit through easily or if they are ions they will be repelled by the non-polar phospholipid tails and so can’t pass through.
Name 2 mollecules that can pass through the bilayer by simple diffusion.
Small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion.
What is meant by facilitated diffusion?
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins (protein channels or transporter proteins) down a concentration gradient.
“Most channel proteins in animal and plant cells are highly selective.” What is meant by “selective” in this context? What implication does this have for specialised cells?
Most channel proteins in animal and plant cells only allow specific mollecules through, not just any. Therefore to perform specialised functions, different cell types have different channel and transporter
proteins.
How can channel proteins change to allow or prevent diffusion?
Some channel proteins are ligand gated or voltage gated and change conformation to allow or prevent diffusion.
What is a ligand gated channel opened/closed by?
Ligand-gated channels are controlled by the binding of signal molecules (ligands) to allow or prevent diffusion.
What is a voltage gated channel opened/closed by?
Voltage-gated channels are controlled by changes in ion concentration.
What is a transporter protein and how does it transport mollecules across the membrane?
Transporter proteins are integral membrane proteins that bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane, down a concentration gradient.
What is meant by “active transport”?
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
What are the difference(s) between active transport and facilitated diffusion? (As much detail as possible).
Active transport uses pump proteins to transport mollecules across the membrane against a concentration gradient so it requires a source of energy. Facilitated diffusion uses channel proteins or tansporter proteins and does not require energy as mollecules are transporeted down a concentration gradient, channels can be ligand or voltage gated.
