Lecture 2 Flashcards
Cell Membrane composed of
Phospholipid Bilayer - Hydrophilic outside and hydrophobic inside
- barrier for water and water-soluble molecules
- proteins - Allows for movement of substances through membrane
5 types of Proteins within bilayer of the Membrane
- Ion channels
- Carrier proteins (picks up a substance at one side of a protein and drops it at the other)
- Pumps (uses energy because against concentration gradient)
- Receptors (allow for communication between cells)
- Enzymes
2 Types of transport through a membrane
- Diffusion (no energy required)
- Active transport (energy required)
Diffusion
Random movement in all directions
2 types - simple diffusion and facilitated diffusion
Simple diffusion
Movement through membrane, channel protein, or pore
Selectivity of channels
Highly selective permeability due to different composition
Gated channels are unique to specific ions.
Na+ gated, Ca+ gated, etc.
Ungated vs Gated Channels
- Ungated channels - always open (specific ion is always diffusing through pore); leak channels (important for electrical signals)
- Gated channels - Open and close in response to a stimulus
Facilitated Diffusion
Required interaction of transported molecule with a carrier protein which aids passage
Diffusion because it still doesn’t require ATP
How do the two types of diffusion, facilitated and simple, differ?
Simple diffusion = exponential rate
Facilitated Diffusion = logarithmic increase (dependent on the rate at which carrier protein can change conformation due to stimulus; Vmax cannot be greater than the rate of this change in conformation)
Net Diffusion
Average direction of diffusion
2 factors that affect the net rate of diffusion
- Concentration gradient (down concentration gradient)
- Membrane electrical potential - electrical potential across membrane is equal in magnitude but opposite in direction to the concentration force (Nernst Potential - EMF (mV) = +/- 61 log (Co/Ci) )
- (+) and (-) ions will affect the rate of diffusion
Osmosis
Net diffusion of water
Osmostic Pressure
Amount of pressure required to counter osmosis (i.e. higher osmolarity = higher osmotic pressure)
In other words, how much pressure is needed to stop osmosis
Lipid-soluble molecules - how do they interact with the cell membrane?
move readily through the membrane (rate depends on lipid solubility) - oxygen, carbon dioxide, alcohol, and steroid hormones
How does water interact with the cell membrane?
Water can pass freely through any channel or pore
Water-soluble ions - how do they interact with the cell membrane?
cross via SPECIFIC water-filled channels or pores
What are the two types of gated channels?
1) Voltage-gated channels - sensitive and dependent; dependent on differences in electrical potentials across the membrane (gate is opened to restore potential difference)
2) Chemical (Ligand)-gated channel - open and close when stimulated by chemical binding (ex: Acetylcholine)
Osmotic pressure determined by
the number of particles present in a solution REGARDLESS of the size or mass
Ex: 1 M of glucose vs. 1 M of albumin. Albumin may be a larger protein, but the osmotic pressure is the same!
Diffusion of water is always from _____ concentration to _____ concentration.
High –> Low
Skeletal muscle nerves will release Acetylcholine which allows sodium to come into the cell. This interaction is an example of what type of gated channel?
Chemical Gated Channel
