Cell membranes Flashcards
L5 L6
What are the components or the basal lamina?
Collagen IV
Laminin
Nidogen
Perlecan
What are the main components of the fibrillar matrix?
Collagen I
Fibronectin
Elastin
Proteoglycans
List the cell junctions present in the epithelial cell.
Tight junction Adherens junction Desmosome Gap junction Hemidesosomes Focal adhesion
What is the shape/ look of desmosomes and hemidesmosomes?
Desmosomes are found as pairs of dark disk-like structure at cell-cell contacts.
Hemidesmosomes look like half of desmosomes: just a single disk instead of a pair.
How big are desmosomes and hemidesmosomes?
Desmosomes are 500nm and hemidesmosomes are 100nm
What diseases can be caused by defects of the 3 cytoskeletons?
Epidermolysis bullosa
Pemphigus
What is the function of hemidesmosome and desmosome?
Hemisdesmosomes link the cell to the extracellular matrix with IF.
Desmosomes link the cell to adjacent cells with IF.
Both of these features give the cells strength against mechanical strength and also give structure.
What is the shape/ look of the tight and the gap junction?
Tight junction: Membranes of two adjacent cells are very tightly attached
Gap junction: Membranes of two adjacent form a slight gap where they’re attached
Where is the tight junction located?
It surrounds the apical part of the cell like a ‘headband’
What is the function of tight junctions?
Acts as a ‘barrier’ because molecules from the extracellular matrix are unable to diffuse past the tight junction into the intracellular space.
Additionally membrane proteins that are apical and basollateral are separated as they cannot pass through the tight junction. This means they’re are properly localised and can carry out their functions. This is known as ‘fencing’.
Where is the gap junction located?
They are dispersed in the lateral region of the membrane.
What is the function of gap junctions?
Ions and small molecules can pass through.
They also allows adjacent cells to be electrically couples (useful for cardiac muscles for example).
What adherins junction?
A transmembrane protein that allow two cells to adhere to each other in a Ca2+ dependent manner
Where is the adherins junction located?
They are found in the lateral domain of epithelial cells as a ‘headband’ underneath the tight junction.
What are Cadherins?
The main component of adherins junctions.
Where are focal adhesions located?
The basal domain of epithelial cells
What is the function of focal adhesions?
The main area where cell is bound to extracellular matrix. They are attached to actin filaments and have integrin which binds to the ECM.
What do focal adhesions do during cell movement?
I dont really know
What can diffuse directly through the membrane?
Hyrdophobic molecules and small polar uncharged molecules.
What is the concentration of the following inside and outside the cell: Na+ K+ Ca2+ Cl-
[Na+] In= 10mM [Na+] Out= 140mM
[K+] In= 140mM [K+] Out= 4mM
[Ca2+] In= 0.001mM [Ca2+] Out= 2.5mM
[Cl-] In= 4mM [Cl-] Out= 140mM
The [K+] In = [Cl-] Out and [K+] Out = [Cl-] In
What does rate of diffusion depend on?
Concentration gradient, membrane permeablity as well as the partition coefficient.
What is the partition coefficient?
Kow - the equilibrium constant for partitioning of a molecule between octanol and water.
Kow > 1 means higher affinity for oil.
Kow < 1 menas higher affinity for water.
The higher the Kow, the faster the solute travels through the bilayer.
How do you find partition coefficient of a solute?
Have your solute of interest, Fill a test tube half with water and half with octanol.
Add solute in and shake the test tube, let phases separate and measure the concentration of solute in lipid phase and octanol phase.
How are K+ channels specialised for K+ only?
Cations in solution are surrounded by water molecules in a very specific way and distance from the cation depends on the ionic radius and nuclear charge.
The K+ channels have amino acids which contain oxygens that are the exact same distance apart as the water molecules would be when the ion is in solution. Therefore, thermodynamically, the is no issue for the K+ to be transferred from solution to the channel whereas if it were a Na+, it would require energy for the Na+ to pass through the channel. K+ could just diffuse through though.
What 4 gated channels are there?
Voltage-gated
Mechanically gated
Extracellular ligand gated channels
Intracellular ligand gated channels
What is uniport, symport and antiport?
Uniport- one solute that is transported
Symport- for movement of one solute to occur, the movement of another solute in the same direction must also occur.
Antiport- movement of one solute is determined by movement of another solute in the opposite direction
How do mechanically gated channels work?
There are cilia attached to the gate and when moved, the gates will be opened.
How do ligand gated channels work?
They can be intracellular or extracellular ligands.
The ligands bind to the proteins to change its shape and allows the gate to be opened.
What is J max?
Maximum transport rate capable of transport proteins
What is Km?
The substrate concentration that gives half the Jmax.
Basically shows the transporter affinity for the substrate.
Where is GLUT 1 found and what are it features?
It is found everywhere, but is abundant in erythrocytes and not so much in skeletal muscles.
It mediates basal transport of glucose to a wide range of cells and has a Km lower than normal blood glucose levels, so has a high affinity for glucose.
Where is GLUT 2 found and what are it features?
In the liver, Pancreatic β-cells.
It has a low affinity for glucose because its Km is high. (Km is roughly 20mM)
Where is GLUT 4 found and what are it features?
It is found in muscles and adipocytes.
It is regulated by insulin
How doe the Na+/K+ ATPase work?
Na+ binds to intracellular site
this triggers an autophosphorylation of the pump.
This causes a conformational change to release Na+ to the exterior and exposes a K+ binding site, which triggers the dephosphorylation of the pump.
Pump returns to original conformation, utilising the energy from the phosphate release and K+ is discharged into the interior of the cell.
3 Na+ leave for every 2 K+ that enter.
