CH 4 Cell Membrane Structure and Cell Transport Flashcards
The plasma membrane
separates the internal environment of the cell from its external environment.
It regulates the entrance and exit of molecules into and out of the cell.
Homeostasis
maintenance of normal internal conditions in a cellular organism by means of self-regulating mechanisms.
The steady internal environment maintained in the plasma mem.
Phospholipid bilayer with embedded proteins includes:
-Hydrophilic (water-loving) polar heads
Face inside and outside of cell (water present)
-Hydrophobic (water-fearing) nonpolar tails
Face each other, away from water
-Cholesterol (animal cells) controls excess fluidity
Peripheral proteins
-associated with only one side of membrane
-form temporary bonds with the cell membrane
Integral Proteins
-span the membrane
-can come from one or both sides
-embedded within the membrane
-able to move laterally (sideways)
What are the attached carbohydrate chains that both phospholipids and proteins can have?
Glycolipids - lipids attached to carbohydrates.
Glycoproteins - proteins attached to carbohydrates.
Channel proteins
Are involved in the passage of solutes through the membrane (substances simply move across)
-Some may contain a gate that must be opened in response to a signal.
-Contains a tube-like opening in the plasma membrane
Carrier Proteins
allow the passage of a solute by combining with it and helping it move across the membrane
Concentration gradient
Going “down” a concentration gradient- From an area of higher to lower concentration
Going “up” a concentration gradient- From an area of lower to higher concentration
Requires input of energy
Examples and description of Passive Transport
- Diffusion
- Osmosis
- Facilitated Diffusion
*No energy needed
*High to Low
*“Down the Gradient”
Examples and description of Active Transport
- Na+/K+ pump
- Endocytosis
- Exocytosis
*Requires energy
*Low to high
*“Up the gradient”
Selectively permeable
The plasma membrane can regulate the passage of molecules into and out of the cell
Molecules can freely cross the membrane and some may require carrier proteins and/or energy depending on…
-Size
-Nature of molecule - polarity, charge
What kind of molecules can freely cross the membrane?
Small, uncharged molecules
Ex: Co2, O2, glycerol, alcohol
-Slip in between hydrophilic heads and pass thru hydrophobic tails
What kind of molecules can’t freely cross the membrane?
Water (which is polar), large molecules, ions, and charged molecules
Aquaporins
Special channels that allow water to cross membrane (present in majority of cells)
Molecules that can’t freely cross membrane can cross via…
-Channel proteins forming a pore through the membrane (facilitated diffusion)
-Carrier proteins that are specific for substance they transport
-Vesicle formation in endocytosis or exocytosis
Diffusion
-Movement of molecules from an area of higher to lower concentration
-Down a concentration gradient
-Occurs until equilibrium is reached
Is there net movement between a solution containing a solute (solid) and a solvent (liquid)?
Once the solute and solvent are evenly distributed, their molecules continue to move about, but there is no net movement of either one in any direction
What factors influence the rate of diffusion?
Temperature (as temperature increases, the rate of diffusion increases)
Pressure
Electrical currents
Molecular size
Osmosis
Diffusion of water through a selectively permeable membrane from high to low concentration (type of diffusion)
Osmotic pressure
The pressure that develops in a system due to osmosis.
The greater the osmotic pressure, the more likely water will diffuse in that direction.
Isotonic Solution
Same concentration of solute (salt) inside and outside of cell
Hypotonic Solution
lower solute concentration outside of cell, water will enter cell
