Module 9 - 1 Flashcards
What are the functions of membranes?
- Separate cells from the external medium to create an intracellular environment of unique and defined composition. 2. Allow selective transport of substrates in and out of the cell. 3. Provide a location for specialized pathways and processes (e.g. energy conversion of mitochondria). 4. Rapid changes in electric potential across the membranes of neurons as basis of the nervous system. 5. Localization of receptors to facilitate response to physiological signals. 6. Mediate cell-cell recognition and interaction.
What are membrane characteristics?
- Membranes are sheet-like structures, two molecules thick, that form closed boundaries between compartments. 2. Membranes consist of mainly of lipids and proteins, with carbohydrates linked to these molecules. 3. Membranes are built from amphipathic molecules. 4. Membranes are largely impermeable to polar molecules. 5. Specific membrane proteins mediate particular biological functions. 6. Membranes are self-assembling, non-covalent structures. 7. Membranes are fluid and dynamic structures. 8. Membranes are highly specialized in their composition and distribution (asymmetric).
What is the basic structural element of membranes?
Lipid Bilayer.
What is membrane formation a consequence of?
the amphipathic nature of membrane lipids
How do membrane lipids self-assemble?
Through the hydrophobic effect.
What does the structure formed depend on?
The ratio of cross-sectional areas of the polar head group and the hydrophobic tail.
What do fatty acids favor?
Micelle formation of micelles.
What do lipids with two hydrocarbon tails tend to form?
Bilayers
What is the energetically unfavorable exposure of hydrophobic tails at the edge of the bilayer to water?
Formation of membrane vesicles.
What are membrane vesicles?
Flat bilayer sheets that fold upon themselves to get away from water and form membrane vesicles with an internal volume
What is the permeability of lipid bilayer membranes?
Very low to ions and most polar molecules.
What is the correlation between permeability and solubility of small molecules?
Permeability of small molecules is correlated with their relative solubility in water.
What molecules can pass directly through the membrane?
Small non-polar gases (O2, CO2)and small hydrophobic molecules (fat soluble hormones).
What is the critical barrier for polar drugs?
The cell membrane.
How can transport of polar drugs across the membrane be facilitated?
Encapsulation within a liposome.
