Cell Biology Flashcards
Cell membrane
Selectively permeable plasma membrane
Composed of a phospholipid bilayer
Function to provide a continuous barrier to separate the cell and its internal components from the external environment.
What is the lipid bilayer selectively permeable for/against?
Permeable to: nonpolar, hydrophobic and uncharged substances (ex: steroids, O2, CO2, N2)
Impermeable to: polar, hydrophilic and charged substances (ex. ions and large proteins)
Exception: permeable to H2O, even though it is polar/hydrophillic
Fluid Mosaic Model
The model usually used to describe cell membrane action.
Membrane is highly fluctuating due to the high rate of fluctuation and movement of the phospholipids.
Membrane Gradient
The chemical difference between the inside and outside of the cell.
If the difference involves ions with charges, the result is a Membrane Potential
Ampipathic properties of phospholipids
Polar, hydrophilic phosphate head, and non polar, hydrophobic, lipid tail.
What is the lipid bilayer composed of?
FATS
- phospholipids (75%)
- cholesterol (20%). Carries an OH- (thus polar) and attaches to phosphate head
- glycolipids (5%). Contains polar carbohydrate and found only on extracellular side of membrane.
PROTEINS
- integral (many are glycoproteins)
- peripheral
What are the roles of the cell membrane glycolipids believed to be?
Signal transduction, cell to cell adhesion, binding
Glyocalyx
Sugary coat created by the carbohydrate ends of the glycoproteins that marks the cell’s uniqueness
What are the 6 functions of proteins in the cell membrane?
- transport
- ion channel
- receptor
- enzymatic
- linkers
- markers
Transporter proteins
Transports polar (hydrophilic) uncharged substances.
Ion channel
Selectively transports ions through the membrane. Very important in nerve impulses. Specific to certain ions.
Receptor
Cellular regulation sites
Ligand
A specific molecule that bonds to a receptor
Enzyme
Integral proteins that catalyze specific reactions at the inside or outside of the cell’s surface
Linkers
Attach to other cells. Example: clotting with linkers attach to surrounding platelets
Markers
Glycoproteins (and glycolipids) that help cells recognize each other, and identify foreign cells
Ex. ABO blood markers
Passive transport
Doesn’t require ATP.
Uses kinetic energy, via electrical or concentration gradients
What are the two main types of passive transport?
Osmosis
Diffusion (can be simple or facilitated)
Why are integral proteins required to help diffuse some ions through the membrane?
Because ions are polar, and thus hydrophilic, they have difficulty moving through the fatty acid tail lipid bilayer.
What are the two ways that diffusion can be facilitated?
Channel or carrier mediation
Osmosis
A special type of diffusion in which a solvent goes from higher to lower concentration through a selectively permeable membrane
Acquaporin
Membrane channel specific to H2O
Osmotic pressure
Pressure exerted by the solvent on the solute side of the membrane. Directly proportional to the concentration of the solute.
Oncotic pressure
Pressure exerted by the presence of colloids (large solutes) in a closed tube. Pulls solves to the side with the higher solute concentration.
Hydrostatic pressure
Pressure exerted by the solvent on its surroundings, usually on the side of the solute.
Opposes osmosis!
Tonicity
Measure of a solution’s ability to change the volume of cells by altering the water content.
Isotonic
Any solution in which a cell maintains its normal shape and volume, because the concentration of solutes is the same inside and outside of the cell.
Hypertonic
Higher concentration of solutes in the surrounding solution. Water tends to leave the cell –> Crenation