Comparison of transport
Comparison of Membrane Transport Systems
Passive Processes
Movement of substances down the concentration gradient (from high to low until equilibrium is reached). No energy is required for any of this processes.
Active Processes
Cellular energy (ATP) is used to pump substances against (up) the concentration gradient – from low concentration of solute to high concentration of solute.
Comparison Chart
| Active | Passive | |
|---|---|---|
| Types of transport | Vesicular transport (endocytosis/exocytosis), Pumps | Small lipophilic molecules, water, small monosaccharides, Oxygen, Carbon dioxide,... |
| Types of particles transported | proteins, ions, large cells, complex sugars | Samll lipophilic molecules, water, small monosaccharides, Oxygen, Carbon dioxide,... |
| Examples | Endocytosis (Phagocytosis, Pinocytosis, receptor-mediated Endocytosis), Exocytosis, Sodium/Potassium-Pump | Simple diffusion, Facilitated diffusion (channel-mediated, carrier-mediated), Osmosis |
| Importance | In eukaryotic cells, amino acids, sugars and lipids need to enter the cell by protein pumps, which require active transport.These items either cannot diffuse or diffuse too slowly for survival. | It maintains equilibrium in the cell. Wastes (carbon dioxide, water, etc.) diffuse out and are excreted; nutrients and oxygen diffuse in to be used by the cell. |
| Functions | Transports molecules through the cell membrane against the concentration gradient so more of the substance is inside the cell (i.e. a nutrient) or outside the cell (i.e. a waste) than normal. Disrupts equilibrium established by diffusion. | Maintains dynamic equilibrium of water, gases, nutrients, wastes, etc. between cells and extracellular fluid; allows small nutrients and gases to enter/exit. |
Major mechanisms by wich molecules cross membranes
| Membrane channel Proteins/Ion channels | Carrier/Transporter |
|---|---|
| Integral membrane proteins that act as in channels (or ion pumps).
Permeability: • voltage-gated (e.g. sodium channel) • ligand-gated (via neurotransmitters) • mechanically-gated (via touch/vibration/strech-sensors) • randomly-gated (percentages of open/closed channels remain constant) • thermo-gated |
Integral membrane proteins wich release the bound molecules tot he other side oft he membrane via change in conformation.
Involve active transport using energy from breakdown of ATP: • Uniport: Only one molecule is transported • Symport: Movement of substance up its concentration gradient in the same direction as its coupling-ion (Na+ glucose transport) • Antiport: Movement of substance up its concentration gradient in the oppsoite direction as its coupling-ion (Na+/H+ transport)
• Carrier-mediated: Movement of small polar molecule down its concentration gradient by a carrier protein (e.g. transport of glucose into cell by glucose carrier)
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Both channel and carrier proteins may facilitate diffusion requiring no energy or may involve active transport requiring energy from ATP.
