1.3a movement of molecules across membranes Flashcards
Fluid mosaic model
A model that describes the structure of the cell membrane.
How are Integral membrane proteins held within the phospholipid bilayer?
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.
What are transmembrane proteins?
Some integral proteins are transmembrane proteins which mean they span the entirety of the cell membrane.
How do Peripheral membrane proteins stay bound to the surface of the membrane?
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.
Phospholipid bilayer
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules. Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion.
Transport channels - Facilitated diffusion
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins.
What are channels and transporter proteins?
To perform specialised functions, different cell types have different channel and transporter proteins.
Channels are multi-subunit proteins with the subunits arranged to form water filled pores that extend across the membrane.
Most channel proteins in animal and plant cells are highly selective. This means they let very few types of molecules pass through.
Some channels are gated and change conformation to allow or prevent diffusion.
Ligand gated channels
Channels which are controlled by the binding of an signal molecules.
Voltage gated channels
Channels controlled by changes in ion concentration.
What are transporter proteins?
Proteins which 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
Active transport
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
A source of metabolic energy is required for active transport.
Some active transport proteins hydrolase ATP directly to provide the energy for the conformational change required to move substances across the membrane. The ATP is hydrolysed by enzymes called ATPases.
What is aquaporin
Protein channels which allow for passive diffusion of water through the membrane.
