Week 1 - Membrane Transport Flashcards
What does the plasma membrane acts as an effective barrier between?
the intracellular fluid (ICF) and extracellular fluid (ECF) compartments
What is the structure in the middle?
Phospholipid bilayer - Hydrophilic head on outside and hydrophobic tails in the middle
Label the extracellular space, and the two plasma membranes
Label the diagram
What does the hydrophobic nature of the phospholipid tails result in?
Prevents the movement of water-soluble substances across the plasma membrane
What allows the movement of certain substances across the plasma memberane?
Membrane proteins which act as channels, receptors, pumps, etc, which move materials in a highly regulated fashion.
What are the two major types of movement across a plasma membrane?
Passive processes (don’t require ATP) and active processes (and do require ATP)
Do passive processes result in substances (without energy and ATP) moving down or up their concentration gradients?
Down the concentration gradients
Why does diffusion occur because of the continual random motion of the molecules?
due to the thermal energy of the system
Substances move from a region of high concentration to a region of lower concentration simply because?
There are more molecules in the region of high concentration which results in a higher frequency of collisions and consequently the progressive migration of molecules into the area of lower concentration until the molecules are evenly distributed.
What does the degree to which a substance can move across the membrane by diffusion depend upon?
- The permeability of the membrane to that particular substance.
- In addition it should be obvious that the bigger the cell, the larger the area of the plasma membrane available for diffusion and consequently the greater the rate of diffusion.
Taking all of these variables into consideration we can say that for any substance the rate of diffusion (usually designated Q) is given by:
Define Simple Diffusion through the Lipid Bilayer
In general, the higher the lipid solubility of a substance, the faster it will diffuse through the plasma membrane.
EXTRA NOTE: Studies of artificial membranes (either synthetic lipid bilayers or cell membranes with all the proteins removed) have revealed that substances which have a high lipid solubility (such as O2, CO2, N2, alcohols and fatty acids) are able to dissolve in the phospholipids of the lipid bilayer and diffuse directly through the plasma membrane.
