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What is the definition of biological membranes

an enclosing or separating membrane that acts as a selectively permeable barrier within living things.


What are the 2 basic functions of bio-membranes?

Barrier function; separate cell from external environment and divide the cell into smaller compartments which have diverse functions.
Metabolic functions; Ensure directed flow of biological processes and carry it out efficiently with high speed due to large surface area.


What are the 4 types of bio membranes?

Natural, Artificial, Intact and Modified.


What are asymmetric biomembranes?

Membranes that have surfaces which vary in structure, function and composition. They are usually found in natural bio-membranes.


Describe proteins in the bio membrane.

They have diverse functions
A molecular mass of 10,000 to 1,000,000 daltons
They are partially or completely submerged in the lipids.


What are the 3 types of Lipids?

Phospholipids, Spingolipids and Steroids


What is the structure of lipids?

They have a polar head which could be neutral or charged with a 2 long non polar fatty acids attached. (Unsaturated or Saturated)


Describe the structure and function of oligosaccahrides

Polymer containing 3-10 monosaccharides. Their main function is for cell binding and cell recognition.


Describe the effect of water when the membrane is free, captured and bonded

When free, the mobile phase is freely exchangeable with water inside and outside the cell.
When captured, the mobile phase is surrounded by lipids which exchanges with water inside or outside the cell very slowly.
When bonded, the the immobile water molecules surround the polar parts of the lipids and proteins due to solvation


What did the Model of Gorter and Grendel conclude?

Membranes are lipid bilayers.


What did the model of Davson and Danielli show?

A double lipid billayer with globular proteins coated on the outside of both layers.


What did the model of Zahler show?

Proteins are floating on both sides of the bilayer and are partially submerged.


What is the lipid bilayer?

The lipids are next to each other forming a bilayer with a hydrophilic head and a hydrophobic tail. (Cytosolic=internal, Extracellular=external).
The bilayer in physiological temperatures stay in a mesomorphous state which ensures membrane fluidity and an ordered structure.


What is the positioning of the 2 types of proteins and carbohydrates on the fluid mosaic model?

Peripheral proteins are positioned on the surface of the bilayer but can also be partially submerged.
Intergral proteins span the whole bilayer.
Carbohydrates are attached to the lipids and proteins on the extracellular surface.


Explain the membrane variability and dynamics of the fluid mosaic model.

There is a continuous replacement of the molecules with new ones aswell as continuous conformation changes and thermal motion of the molecules.(Fluidity)
The proteins have a half life of 2-140 hours while the lipids have a half life of 14-80.


What can the composition, shape and structure of artificial membranes be?

The can be composed of lipids only or lipids,proteins etc.
There membrane shape can be flat or spherical.
Their membrane structure could be monolayer, bilayer or multilayer.


What are flat monolayer artificial membranes?

They are formed on a water-air boundry by a single layer of lipids.
They are used to investigate the state of lipids at different temperatures, the occupation of lipid molecules in a single states and the effect of medicinal substances on the lipid bilayer.


What are flat bilayer membranes?

The membranes surfaces are both in contact with water.
They are used to study the electrical resistance of membranes, generation of surface electric charge on membranes.


What causes spherical membranes and what are 2 examples?

Water dispersion of
Micelles are a monolayer spherical membranes
Liposomes are spherical membranes consisting of 1 or more bilayers.


How can liposomes be applied?

They can be used to investigate lipid bilayer structures and permeability of membranes to various substances.