Transport mechanisms Flashcards
What is the cell membrane highly permeable to? (4)
-H2O
-lipid-soluble substances
-dissolved gases (O2, CO2)
-small uncharged molecules.
What is the cell membrane less permeable to? (2)
-larger molecules
-charged particles
What is the cell membrane impermeable to? (1)
Very large molecules
What is the structure of the cell membrane?
The bimolecular phospholipid layer
Describe the polarity of the cell membrane.
Amphipathic
Polar and Nonpolar ends
Why is cholesterol inserted in the phospholipid bilayer? (3)
-reduces packing of fatty acid tails
-tends to increase membrane fluidity keeping fatty acid tails apart
-May also be involved in the formation of vesicles that pinch off the plasma membrane and in lipid rafts.
Describe the polarity of the cholesterol
Slightly amphipatic
How does cholesterol function at high and low temperatures?
At high temperatures, cholesterol acts to stabilize the cell membrane and adds firmness;
while at low temperatures, it inserts into phospholipids and prevents them from interfering
with each other to avoid aggregation
What is the difference between integral and peripheral proteins in the cell membrane?
Integral proteins are closely associated with phospholipids and mostly cross the membrane,
while peripheral proteins are more loosely associated and mostly found on the cytoplasmic
side.
What is the glycocalyx in the cell membrane?
The glycocalyx is a layer of carbohydrate formed by a chain of monosaccharides that extend from the extracellular surface of the cell membrane.
What is the function of the glycocalyx?
-provides protection from infection
-enables cells to identify each other and interact.
What are the functions of plasma membrane proteins ? (6)
- Transport and diffusion of specific molecules into and out of the cell.
- Act as enzymes that catalyze membrane associated reactions.
- Serve as receptors for receiving and transducing chemical signals from the
cell environment. - Cell surface identity markers
- Cell – cell adhesion
- Attachment to cytoskeleton
What are the two types of transmembrane transport
pathways?
-Via phospholipid bilayer
-via interaction with protein cluster (channel or carrier).
What are the two types of transport mechanisms
across the cell membrane?
Passive (energy independent) and active (energy
dependent).
What are the passive transport mechanisms? (3)
- Diffusion
- Carrier-mediated Facilitated Diffusion
- Osmosis
What are the active transport mechanisms?
- Carrier-mediated Active Transport
a) Primary
b) Secondary - Exocytosis
- Endocytosis
What is simple diffusion?
Simple diffusion is the movement molecules from one
location to another as a result of random thermal motion.
What is flux?
The amount of particles crossing a surface per unit
time.
What is the direction of net flux in diffusion?
From high concentration to lower concentration.
What is the net flux in diffusion at equilibrium?
zero
What is the condition for diffusion to occur in the
presence of a mechanical partition?
The partition must be permeable to diffusing
particles.
What is the equation for Fick’s Law of Diffusion?
J = PA (C0 - Ci).
What does J represent in Fick’s Law of Diffusion?
Net flux, or the rate of diffusion.
What is the relationship between diffusion time and
the distance traveled by solute molecules?
Diffusion time increases in proportion to the square
of the distance traveled by the solute molecules.