Selective permeability of membrane
- The molecular organization of the membrane selects what can go in or out of the cell
What is permeable across the cell membrane
- Non polar, uncharged molecules(O2, N2, benzene)
- Lipid soluble molecules (steroids, fatty acids, some vitamins)
- Small uncharged polar molecules( water, urea, glycerol, Co2)
What is impermeable across the cell membrane
- Large uncharged polar molecules( glucose, amino acids, ions)
Diffusion meaning
- Net movement of random mixing of particles kinetic energy from high concentration to low concentration.
What is diffusion driven by?
- A concentration gradient
Greater difference in concentration between 2 sides of the CM the rate of diffusion would be
- Faster
High temperature causes a fast or slow rate of diffusion
- A faster rate of diffusion across CM
Larger molecules & increasing diffusion distance through the CM causes a slow or fast rate of diffusion?
- Slower rate of diffusion
What are the physical consequences of diffusion
- Increase diffusion
- Sets a limit to the size of the cell( 20um thick)
- membrane thickness
- Very fast over small distances
Alternative name for cell membrane
- Two-dimensional fluid
What are the main constituents of the CM
- Phospholipids & proteins
Lipid bilayer structure
- Polar head groups that are hydrophilic
- Non-polar fatty acid tails that are hydrophobic
Amphipathic means
- Each molecule of the phospholipid bilayer have both polar & non-polar region
What does the cell membrane allow by controlling the passage of substances into & out of the cell?
- Concentration gradients are maintained
- Organization of chemical and physical processes in the cell
- Controlled up-take of nutrients & discharge of water products & secretion of molecules
- Develops a membrane potential
Membrane fluidity meaning
- The free movement of protein & lipid constituents within the CM
Fluidity is determined by
- lipid tail lengths
E.g: Longer tail > Less fluidity > less permeable
Two basic classes of membrane proteins
- Integral Membrane proteins
- Peripheral Proteins
Integral membrane proteins structure
- Extend or completely across the cell membrane (transmembrane protein)
- They are amphipathic
- Hydrophilic ends of the proteins interact with the aq solution
Peripheral proteins structure
- attached to either the inner or outer surface of the cell membrane
Membrane proteins can act as (RCLECT)
- Receptors
- Cell identity Markers
- Linkers
- Enzymes
- Channels ions
- Transporters proteins
What percent does the cell use of resting energy to maintain concentration and electrical gradients
- 30% of resting energy
The movement of a non-polar molecule will diffuse across down or against its concentration gradient
- Down it’s concentration gradient
Electrical gradient meaning
- a gradient of electrochemical potential for an ion that can move across a membrane
How can cells maintain a difference in charged ions between the inside & outside of the membrane
- Electrical gradient or membrane potential
