Transport Mechanisms Flashcards
In Transport Mechanisms, in which part of the cell are we particularly interested in?
The Cell Membrane
What are the Permeability Characteristics of the Cell Membrane?
Highly permeable to:
- H20, Lipid-soluble substances, Dissolved Gases (O2, CO2) and small uncharged molecules
Less permeable to:
- Larger molecules and charged particles
Impermeable to:
-Very large molecules
Describe the Cell Membrane.
It has a Phospholipid Bilayer with hydrophilic heads (polar, on the outside) and hydrophobic tails (non-polar, on the inside)
What are hydrophilic heads composed of?
Carboxyl and hydrogen
What are hydrophobic tails composed of?
Tricglycerides and cholesterol
What is cholesterol’s function for in the Cell Membrane?
Acts as a buffer to prevent lower/increase TEMPERATURES for inhibiting/increasing FLUIDITY.
Involved in formation of vesicles that pinch off the plasma membrane
There are 2 types of protein pertaining to the Cell Membrane. What are they and where are they located?
Integral proteins: Closely associated with phospholipids (Trans-membrane)
Peripheral proteins: loosely associated on the cytoplasmic side
What is glycocalyx and what are it’s main functions?
It’s a fuzzy coating surrounding the cell membrane formed of glycans, glycoproteins and glycolipids
Functions: Contributes to cell-cell recognition, communication, adhesion and protection. Helps control vascular permeability
What are the functions of Plasma Membrane Proteins?
They act as selective or enzyme transporter, cell surface receptor or identity marker and cell-cell adhesion or attachment to the cytoskeleton
What are the 2 transmembrane pathways?
- Via the phospholipid bilayer
- Via interaction with a transmembrane protein
There are 2 Cell Membrane Transport Mechanisms. What are they and by which mechanisms?
- Passive (energy indepedent): Diffusion, Facilitated Diffusion and Osmosis
- Active (energy dependent): Active Transport (primary,secondary) and Pino/Phagocytosis
What is Diffusion?
It’s the movement of molecules from one location to another as a result of random thermal motion.
It happens even in the presence of a mechanical partition (membrane) as long as it is permeable
How does diffusion flux and net flux work?
Diffusion flux: It’s the amount of particles crossing a surface per unit time
Net flux: Movement of particles from high to low concentration
What happens to diffusion flux and net flux at equilibrium?
Diffusion flux: They become equal
Net Flux = 0
How does diffusion relates in terms of time and distance?
Diffusion time increases in proportion to the square distance travelled by the solute molecules
What affects Cell Membrane Diffusion?
- Mass of molecule
- Concentration gradient
- Lipid Solubility
- Electrical charge
- Ion Channels
- Membrane carriers
How can diffusion happen at the cellular level and what is it related to?
- Diffusion across the lipid bilayer
- Diffusion of ions through channels
It is related to the concentration gradient
What are Ion Channels?
Transmembrane proteins that show ion selectivity
How is the movement of an ion is affected?
By the presence of an electrical gradient and it’s own concentration gradient = electrochemical gradient
Ion channels can exist in open or closed state and may be gated but in what ways?
- Ligand gated (chemical messengers)
- Voltage gated
-Mechanically gated
Name the different Voltage Gated Ion Channels
Na+ channels
K+ channels
Ca+ channels
Cl- channels
Current flow through single ion channels depends upon what?
- Channel conductance
- Channel open time
- Frequency of channel opening
What is Mediated Transport?
The movement of ions and other molecules by integral membrane proteins called transporters or carriers.
What are the characteristics of Mediated Transport?
- Specificity (1 type of molecule transported)
- Saturation (Rate of transport when all binding sites are occupied - Transport max)
- Competition (When similar substances compete for binding sites)
