Transport across Membranes Flashcards
In terms of the plasma membrane what is different between eukaryotic and prokaryotic?
Eukaryotic cells have internal compartmentlisation via plasma membranes as well as an outer membrane.
What are the functions of a plasma membrane other than compartmentilising?
-Receiving information
-Exporting and importing small molecules
-Facilitating movement and expansion
How is the structure of the membrane termed? What is the general structure?
Fluid mosaic model
A phospholipid bilayer to create an impermeable surface and fulfills a structural purpose
Proteins spanning the membrane are the functioning units of the membrane
What is the generic structure of a phospholipid?
A polar/hydrophilic head containing in descending order (the top in contact with aqueous environment) a choline group, phosphate group and a glycerol group
Two non-polar/hydrophobic tails: one saturated one unsaturated fatty acid.
Apart from phospholipids and proteins what are the other components of the membrane?
Steroids such as cholesterol and glycolipids
What is the purpose of the unsaturated fatty acid chain?
The unsaturated (has double bond(s) makes the membrane have more fluidity by increasing the distance between the fatty acids making the membrane looser. This allows the embedded proteins to move around the membrane (slightly).
The membrane is not a static structure.
What does amphipathic mean?
A molecule that can be both hydrophobic or hydrophilic (phospholipids)
What are the different categories of membrane proteins?
Transporters and channels
Enzymes (most often are peripheral to the membrane and more likely to be associated with the hydrophilic component and sit inside the cell)
Receptors (interact with ligands to create signal cascades)
Anchors (often interact without cytoskeletal components)
What molecules are membranes permeable to and which need extra steps to facilitate transport?
Membranes are very permeable to small uncharged/nonpolar molecules.
A few small uncharged polar molecules are able to pass through the membrane, for larger uncharged polar molecules fewer still can pass the membrane.
All charged molecules (ions) cannot cross the membrane.
Polar molecules will often need a transporter and ions will need pumps.
In terms of physiology ions must be in set locations until a determined stimulus makes that change.
What is required of particles to be able to diffuse across the membrane?
They either need to be hydrophilic or not be effected by the hydrophilic properties of the lipid membrane. (CO2, O2 and some H2O)
What is facilitated diffusion?
The movement of polar or charged molecules generally performed by channel proteins or carrier proteins.
What are the key aspects of channel proteins?
They have an aqueous, hydrophilic pore in the middle which allows molecules to travel through as it provides an energetically favourable environment
Their resting state is closed.
A ligand (stimulus molecule) will open the channel via stimulating a conformational and allows for molecules to enter the cell by following the concentration gradient.
[] -> [ ] -> []
What are the key aspects of carrier proteins?
The molecule to be transported will interact with the protein stimulating a conformational change that allows the molecule to pass through the protein following the concentration gradient.
Think of it a bit like an airlock
Open the airlock from inside, O2 rushes
Airlock closes
Airlock opens to outside O2 ejected
[] -> \/ -> /\ -> []
What is GLUT 4 and how is regulated?
A glucose transporter.
Insulin (the ligand) will bind to a receptor on the membrane causing a phosphorylation signal cascade which send lots of information internally to the cell. This leads to vesicles taking GLUT 4s and fusing them to the membranes. This increases the movement of glucose into the cell
What are the different categories of active transporter proteins?
Uniporter - one substance in one direction
Symporter - two different substances in the same direction
Antiporter - two different substances in opposite directions
