Membranes Flashcards
What are the functions of a cell membrane?
- Selective barrier to the passage of molecules
- Detecting Chemical signals
- Anchoring cells to adjacent cells and to the extracellular matrix of connective tissue proteins
How thick are cell membranes?
6-10mm
What are are membranes mostly comprised of?
phospholipids
How are phospholipids organised in the plasma membrane?
In a bilayer with the non-polar fatty acid chains in the middle
What else does the plasma membrane contain that intracellular membranes do not contain much of?
Cholesterol
What are the two classes of membrane proteins?
Integral and Peripheral
What does it mean for phospholipids to be amphipathic?
They have both hydrophobic and hydrophilic parts
What are the 3 types of junctions that cells are physically joined by?
Desmosomes
Tight Junctions
Gap Junctions
What are integrins?
Transmembrane proteins which bind to specific proteins in the ECM and link them to membrane proteins on adjacent cells
What are Desmosomes?
Dense plaque accumulation along cytoplasmic surface that serve as anchoring points for cadherins, which link up and bind to cadherins in adjacent cells
What is the function of a desmosome?
Hold adjacent cells firmly together in areas that are subject to considerable stretching such as the skin
What is a tight junction?
Where two adjacent plasma membranes join so no extracellular space remains between them
What is a gap junction?
where Connexins from the two membranes join, forming small protein lined channels lining the cytosol of the two cells
what is Diffusion?
random thermal motion causing movement from one location to another
what is flux?
The amount of material crossing a surface in a unit of time
What is net flux?
The difference between the two one way fluxes. The overall movement of material from one compartment to another
What factors affect the magnitude of flux?
- Temperature
- Mass of molecule
- Surface area
- Medium through which the molecules are moving
What is the major limiting factor for diffusion across a membrane?
The non-polar/hydrophobic interior of the bilayer
What can diffuse through the plasma membrane bilayer?
hydrophobic/non-polar substances
What is the specificity of an ion channel determined by?
Pore size, charge and binding sites
What is membrane potential?
The separation of electrical charge across a membrane
What is the direction and magnitude of ion flux dependent on?
Concentration difference
Electrical difference
What are the types of gated channels?
- Ligand gated
- Voltage gated
- Mechanically gated
What factors determine the magnitude of solute flux through a mediated system (of carriers/transporters)
- Saturation of binding sites
- Number of transporters
- Rate at which conformational change occurs
What are the two kinds of mediated transport systems?
- Facilitated diffusion
- Active Transport
What is facilitated diffusion
the net flux of a molecule across a membrane from higher concentration to lower concentration until the concentrations are equal
What is active transport
The use of energy to move molecules against the concentration gradient
How does Active Transport work?
ATP is hydrolysed, phosphorylating the transporter causing covalent modulation and a conformational change in the molecule and changing the affinity of the solute to the binding site
What are aquaporins?
Proteins which mediate the diffusion of water across membranes
What is Osmosis?
The net diffusion of water across a membrane
What is Osmolarity?
The total solute concentration of a solution
What is one osmol equal to in mols of solute particles?
1 mol
