Flashcards in Mechanical properties of biomembranes Deck (23):
Describe the thickness of bio membranes.
Thickness is measured by xray scattering which is upto 11nm or electron microscope which shows up to 7nm.
Mechanical factors do not effect membrane thickness.
Electron microscopes show that membranes have 3 layers, 2 dark dense layers with a thickness of 2nm each and 1 light layer between them with a thickness between 3-3.5nm.
What is elasticity?
Ability of a biomembrane to support mechanical stress when bent or stretched.
What is the modulus of compression( Area compression modulus)?
The ratio of mechanical stress to strain in an elastic material when that material is being compressed
modulus of compression=
compression force per unit area/change in volume per unit volume.
What is the bending modulus(Flexural modulus)
intensive property that is computed as the ratio of stress to strain in flexural deformation, or the tendency for a material to resist bending.
What is the ultimate strength of biomembranes?
Membranes stretch by less that 2%(By area) before they tear.
Increasing internal pressure changes the cell shape up to spherical bu the area does not change.
High pressures quickly destroy the membrane.
How can you measure membrane viscosity and what does the diffusion constant depend on?
Stokes einstien equation;
d= diffusion constant
r= radius of diffusing molecule.
The D depends on the microscopic structure of the membrane. Viscosity varies over the membrane.
Describe the permeability of bio-membranes.
Biomembranes are permeable to water and neutral lipophilic substances.
They are poorly permeable to hydrophilic subtances.
They are partially impermeable to charge molecules and small ions.
Membrane permeability depends on the concentrations of various lipids.
What does the physical properties of biomembranes depend on?
They depend on the properties of the molecules building the membrane; size,shape,polarity, arrangement in space, charge.
Describe the molecular structure of lipids.
A glycerol molecule with a phosphate group attached with also 2 fatty acid chains or carboxylic acids.
What causes the variance in electric charge on the polar head?
Lipid heads may be zwitterions. This means they hold a positive and negative charge with no net charge.
Lipids such as phosphatidylserine and cardiolipin carry charges. (1 negative and 2 negative charges respectively)
Describe the structure of the non polar tail.
Chains of 14-22 usually being 16 or 18. Can be saturated or unsaturated.
Describe the amphiphilic properties of lipids.
Lipids are amphiphilic due to their hydrophobic tails and hydrophilic heads.
Their bilayer organisation exists to minimise the potential energy of the interactions between them and water.
What is the mesomorphous state of lipids ?
The liquid crystalline state is when the lipids are fluid and anistrophic and are stable in a limited temperature range
What is the phase transition temperature and what are the factors that effect it.
This characteristic temperature is when the lipids change from a solid gel to a liquid crystalline state.
The temperature depends on the chain length of fatty acids and the amount of double bonds in them.
44-86 for saturated, -49-13 for unsaturated.
What are the states of lipids in biomembranes?
Under normal temperatures, both mesomorphous and gel states are present in the membrane.
Changes in the temperature or degree of unsaturation causes a change in the ratio of gel to crystalline states changing the mechanical properties of the membranes.
What is segmental motion?
It is also known as flexion. It is a contraction movement.
Explain Rotary motion.
The individual lipid rotates around its axis. Time for rotation by 1rad: 10^-7s in gel phase and 10^-9 in liquid phase.
What is Lateral diffusion?
The lipid molecule of the biomembrane transpose with the neighbouring lipid in the same plane.
What is Transversal motion?
Also known as transverse diffusion
It is the movement of the lipid molecule from one half of a mono-layer to the other.
This motion is related to the formation of hydrophilic pores in the membrane.
What are the 4 classification of proteins by function?
Enzymes, Transporter, Receptor and Structural.
What are the 2 types of proteins related to their location?
Peripheral proteins(Surface) which is bonded to the bilayer via electrostatic forces.
Intergral(Transmembrane)- bonded to the lipids by hydrophobic forces.
Describe the structure of membrane proteins.
They are globular molecules with masses reaching upto 1,000,000 Da.
Most membrane proteins tend to be peripheral but can also be other conformations such as transmembrane.