Chapter 3 Lecture 4 - Membrane Transport types and tonicity and osmolarity Flashcards
Selective permeability
Allows certain things through, some not
4 movement types
- Filtration
- Diffusion
- Osmosis
- Carrier mediate transport
3 Passive Transport types
- Filtration
- Diffusion
- Osmosis
2 Active transport types
Carrier-mediated transport
Vesicular transport
Types of carrier-mediated transport
- Facilitated diffusion
- Active transport
- Secondary active transport
Filtration
Physical pressure forces fluid through selectively permeable membrane
Examples of filtration
Coffee filter, Capillaries
Diffusion
Net movement of particles from high to low
Rate of diffusion depends on
- Steepness of concentration gradient
- Viscosity
- Temperature (higher temperature, faster rates)
- Molecular weight
- Membrane surface area
- Permeability
- Number of ion channels
Osmosis
Diffusion of water across selectively permeable membranes
Aquaporin
Water channel proteins
Rate of osmosis depends on
relative concentration of the non-permeating solutes on either side of the membrane
Vesicular transport
Movement of molecules in/out of cell in vesicles
Vesicles
Small, liquid/cytoplasm filled structures surrounded by bilayer
What is vesicular transport used for
Movement of large or many molecules and fluid droplets
Types of vesicular transport
- Endocytosis
- Exocytosis
- Transcytosis
Endocytosis
Taking in substances
Types of Endocytosis
- Phagocytosis
- Pinocytosis
- Receptor-mediated
Exocytosis
Expultion of substances
Transcytosis
From 1 side of the side to another
Phagocytosis
Cellular eating, engulfment of particles within phagosome using pseudopods
Phagosome
Type of vesicle that’s in the cytoplasm surrounded by membrane
Where does phagocytosis happen
In few specialized cells
Steps to phagocytosis
- Pseudopods extend around target
- Pseudopods fuse to form phagosome
- Phagosome fuses with lysosome, forms phagolysosome
- Target particles digested
Pinocytosis
Cellular drinking, brings fluid in cell
Where does pinocytosis happen
In all cells
Steps to pinocytosis
- Cell membrane dimples inward
2. Ends of dimples fuse to form pinocytic vesicle
Examples of cells in which pinocytosis commonly happens
Endothelial cells of capillaries, kidney and liver
Receptor mediated endocytosis
Receptors and ligands initiate vesicle formation
Steps of receptor mediated endocytosis
- Ligands bind to receptors on membrane
- Receptors cluster together
- Plasma membrane sinks inward to form pit with peripheral protein called clathrin
- Pit separates from membrane to form clathrin coated vesicle
Clathrin
Address label to direct vesicle to right place or to tell the cell what to do with vesicle
Steps to exocytosis
- Waste vesicle travels to plasma membrane
- Vesicle binds to membrane via linking proteins
- Membrane caves in toward vesicle
- Membrane and vesicle fuse
- Molecules released
How does transcytosis work
Combines endo and exocytosis to take molecules into the cell and then take them out at another place
Where is transcytosis common
In absorptive cells
Osmolarity
Osmotic concentration of body fluids
How is osmolarity calculated (words)
Quantity of osmotically active particles (solutes) per liter
What is osmolarity expressed in
mOsm/L
Tonicity
Ability of a solution to affect the fluid volume/pressure of a cell
Examples of calculations of osmolarity
- Glucose does not dissolve in water, forms 1 molecule in H2O, 1mM of glucose = 1mOsM (milliosmolar) of glucose
- NaCl dissolves into N+ and Cl- in H2O, usually forms 2 molecules, 1mM of NaCl = 1.8mOsM of NaCl
Human body osmolarity
280-296 mOsM
Isosmotic/Hyperosmotic/Hypoosmotic (What do they compare)
Comparative, compare osmolarity of any solutions
Isosmotic
Equal number of particles per unit volume
Hyperosmotic
More dissolved solutes
Hypoosmotic
Fewer dissolved solutes
Hypotonic
Causes cell to swell with fluid, less non-penetrating solutes
Isotonic
No change, equal non penetrating solutes
Hypertonic
Causes cell to shrink, more non penetrating solutes
What is an equally important factor of tonicity
Type of solute
What kind of solute contributes to tonicity
Non permeating
Osmolarity VS Tonicity
Osmolarity is quantifiable, compares any two solutions, tonicity is strictly comparative, only for solution to cell, osmolarity alone DOES NOT predict tonicity
Rules of relationship of osmolarity to tonicity
Hyperosmotic are not always hypertonic but hypoosmotic solutitons are ALWAYS hypotonic