Unit 1 - Topic 3 - Membrane Proteins - Section A - Movement of molecules across membranes Flashcards
What is the fluid mosaic model
The fluid mosaic model describes the structure of the plasma membrane. The phospholipid bilayer can move so it is fluid and the different proteins are like small pieces of a mosaic.
Describe the structure of the plasma membrane
The phospholipid is the basis of the system as it has a hydrophilic head and hydrophobic tails. The head is toward the aqueous cytoplasm and extracellular fluid while the tail is towards the inside of the bilayer.
What do regions of hydrophobic R groups allow
Strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer
Integral membrane proteins interact extensively with what
The hydrophobic region of membrane phospholipids.
What are some integral membrane proteins
Transmembrane proteins
Describe peripheral membrane 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 what
The surfaces of integral membrane proteins
What is the phospholipid bilayer
Is a barrier to ions and most uncharged polar molecules
What molecules can pass through the bilayer by simple diffusion
Some small molecules, such as oxygen and carbon dioxide
What is facilitated diffusion
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins
To perform specialised functions what do different cell types have
Different cell types have different channel and transporter proteins
What are most channel proteins in animals and plant cells
Highley selective
What are channels
Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane.
What are some channels proteins
Some channel proteins are gated and change conformation to allow or prevent diffusion
What are ligand-gated channels controlled by
The binding of signal molecules, and voltage-gated channels are controlled by changes in ion concentration
How do transporter proteins work
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
What do transporter proteins 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 type of protein does active transport use
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient
What are pumps that mediate active transport
Pumps that mediate active transport are transporter proteins coupled to an energy source
What is required for active transport
A source of metabolic energy
What do ATPases do
Some active transport proteins (ATPases) hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane
