membrane transport Flashcards
How is water distributed in a human?
In a typical 70kg male the total body water is approximately 42 litres (thats approximately 60% of the total body weight)
That 42 litres you’ll notice is distributed between the intracellular and extracellular compartments.
There’s about 25 litres in the intracellular compartment so you’ll find this water inside cells, and about 17 litres is found in the extracellular compartment bathing the cells.
The Extracellular compartment is composed of three smaller compartments called the interstitial, the plasma and the transcellular
The interstitial compartment composes about 75% of the extracellular compartment so 16% overall. This fluid baths the non blood cells of the body
The 2.5Litres of blood cells also called haematocrit get bathed by plasma and this is approximately 20% of the Extracellular fluid or about 3 Litres.
what is osmosis?
Passive movement of solvent to a region of high solute concentration across a semipermeable membrane (impermeable to solutes).
what is Osmolarity (osmotic potential)
Total concentration of dissolved particles in a litre of solution.
e.g. 1mol NaCl in 1l H2O has an osmolarity of 2osmol.l-1 (ideally!).
Osmotic pressure is the force produced by differences in osmolarity.
what is osmolality?
Total concentration of dissolved particles in a kilogram of solution.
Measured in osmol.(kgH2O)-1. This is the preferred measurement as it is independent of temperature.
what is isotonic?
when the solute concentration inside and outside the cell is equal.
what is hypertonic?
when the solute concentration is less inside the cell than outside the cell.
what is hypotonic?
when the solute concentration is greater inside the cell than outside the cell.
what is passive diffusion?
A simple passive transport of molecules across a biological membrane. Usually the molecules are small and non-polar.
what is facilitated diffusion?
The passive movement of molecules or ions across a plasma membrane using a transport protein (either a channel or carrier) in the plasma membrane
Describe the molecular structure of membrane lipids
The cell membrane is composed primarily of phospholipids
They are composed of
Glycerol backbone
2 hydroxyl groups (-o-) which are esterified to
Various acyl or fatty acid groups
For glycerol based phospholipids the third glycerolic hydroxyl group is esterified to a phosphate
The phosphate is esterified to the head group
The temperature at which the bilayer converts from a gel state to sol state is called the?
transition temperature
At lower temperatures the phospholipids…
diffuse slowly in gel state
At higher temperatures the phospholipids…
diffuse rapidly in sol state
what are some characteristics that affect the phospholipid bilayer?
Saturated fatty acid chains interact with each other and require more thermal energy to break the interactions and permit diffusion.
Shorter chains and double bonds (kinks) cannot line up next to each other as well and so are easier to move around
Explain how the properties of a membrane are influenced by the presence of cholesterol
Cholesterol is another important membrane lipid because at low concentrations its steroid rings bind to and partially immobilise fatty acid tails making membranes more ridged and increasing the gel-sol transition temperature
At high concentrations cholesterol disrupts the ability of the phospholipids to interact with themselves and increases the fluidity lowering the gel-sol transition temperature
This is significant as human cell membranes can contain large amounts of cholesterol.
List the important physiological functions of the lipid bilayer
Physical barrier that separates the inside of the cell (intracellular fluid/cytosol/cytoplasm) from the extracellular fluid- physical isolation
Controls the entry and exit of ions, the entry of nutrients and the exit of waste- regulation of exchange with environment
Detect chemical messengers arriving at the cell surface- communication with environment
Anchor cells to the cellular matrix- structural
what is the Nernst equation and what is it used to find?
It is used to find the equilibrium potential of an ion.
what is the Goldman-Hodgkin-Katz Equation and what is it used to find?
it is used to find the membrane potential.
Which ion has the highest membrane permeability at rest?
Potassium
what does the sodium potassium atpase do?
it pumps 3 Na+ ions out and 2K+ ions in using ATP to enable resting membrane potential to be reached at -70mv again from -65mv caused by leak channels.
what do leak channels do?
They allow specific ions to move down their concentration gradients.
How does the Gibbs-donnan effect work?
Simple diffusion theory would state that sodium would diffuse from an area of high concentration to an area of low concentration until the two sides were of equal concentrations. This is known as the chemical potential
However, in a biological tissue, we often have negatively charged proteins on one side of the membrane (typically in higher concentrations inside the cell), which are impermeable to the membrane
These negatively charged ions will attract the positively charged sodium, creating a pull in the opposite direction to the concentration gradient. This is known as the electrical potential
This in essence is the Gibbs-Donnan effect, where the effects of oppositely charged particles work against a concentration gradient to create an uneven distribution of ions within a solution
If the opposing forces are equal, such that there is no net movement across the membrane, we call this the equilibrium potential, and we can calculate this using the Nernst Equation
what is ficks law of diffusion?
Size of the difference in concentration gradient
Thickness of the membrane
Permeability of the membrane
Distance of diffusion
