Biochemistry - Transport Mechanisms Flashcards
Energy of passive vs active transport
- Passive: no energy required
- Active: energy required
Movement of materials relative to concentration gradient (passive vs active)
- Passive: high to low (with concentration gradient)
- Active: low to high (against concentration gradient)
Simple diffusion
- Net movement of materials from an area of high to low concentration
- All gas and liquid particles partake in it all the time
- Random
Facilitated diffusion
- Transport of ions and polar molecules through a membrane via protein complexes
- Channel proteins or carrier proteins may be used
Osmosis
- Passive diffusion of water across a membrane
- Water moves from an area of low solute concentration to an area of high solute concentration
- Results in equal solute concentrations on either side of membrane
Factors that affect the rate of diffusion
- Temp: more heat = faster movement of particles
- Distance travelled: smaller distance = faster movement
- Mass of particles: lower mass = less energy needed to make them move faster
- Density of medium: denser medium = more difficult for particles to move through it, diffusion through gas is faster than liquid
- Concentration gradient: the bigger the difference, the steeper the concentration gradient, the faster the molecules will diffuse
Equilibrium (net movement of materials)
Molecules of a substance are moving equally in both directions (equal concentrations in both areas)
Channel proteins
Provide a “tunnel” through the membrane through which the molecules can diffuse
Carrier proteins
Change shape when their specific particle binds, change of shape moves particle across membrane
Isotonic solution
- Concentration of solutes is equal on both sides
- Water moves back and forth but amount of water on each side doesn’t change
Hypotonic solution
- Less solutes outside the cell than inside
- Water moves into the cell
Hypertonic solution
- More solutes outside the cell than inside
- Water moves out of cell
Aquaporin
- Membrane proteins that provide a means for water to travel through a membrane following its concentration gradient
- Specific to water because water is polar and cannot directly diffuse through cell membrane
Primary active transport
- Energy in form of ATP molecules is used to move materials across membrane
- ATP is used to change shape of transport protein, allowing it to shuttle materials across membrane
- Creates concentration gradient (represents stored energy that can be used for secondary active transport)
Secondary active transport
- Uses energy of high concentration gradient of one substance to move other substances across membrane
- May use concentration gradient to shuttle substances in same direction (symport proteins) or in opposite directions (antiport proteins)
Influence of ATP on membrane proteins
- Energy from ATP molecule is used to change conformation of transport proteins, allowing them to shuttle substances across cell membranes
Example of primary active transport
Na/K Pump
- Necessary for nerves + muscles to function
- Pump binds to 3 sodium ions and ATP molecule
- ATP splitting provides energy to change channel shape, sodium ions are driven through channel
- Sodium ions released outside of cell membrane, new shape of channel allows 2 potassium ions (from outside) to bind
- Release of phosphate allows channel to revert to its original form, releasing potassium ions on inside of membrane
Proton pump
- ATP is used to move H+ ions across membrane, building up a concentration gradient
- Creates a charge gradient and pH gradient
Symport protein
- Secondary active transport
- Shuttles substances in the same direction
Antiport protein
- Secondary active transport
- Shuttles substances in the opposite directions
Exocytosis
- Secretory vesicles move through cytosol + contact cell membrane
- Vesicle membrane fuses with cell membrane, releasing contents of vesicle into cell exterior
- All eukaryotic cells partake in exocytosis
Endocytosis
- Proteins + other substances trapped in pit-like depression that bulges inward from cell membrane
- Depression pinches off as an endocytic vesicle
- Three pathways: bulk-phase, receptor-mediated, phagocytosis
- Most eukaryotic cells partake in endocytosis
Bulk-phase endocytosis
- Extracellular water taken in along with molecules in solution in the water, membrane folds inward which encloses solute and water molecules
Receptor-mediated endocytosis
- Molecules (proteins or molecules carried by proteins) bind to outer cell surfaces by receptor proteins
- Receptors collect into a pit coated in clathrin (protein network) that reinforce cytosol side
- Pit breaks free, vesicle loses clathrin coating and may fuse with lysosome
- Enzymes within lysosome digest cargo, breaking down into smaller + useful molecules
Phagocytosis
- Psuedopods engulf particles to be brought into cell, forming vesicle containing particles within cell
- Cells use phagocytosis to engulf bacteria, parts of dead cells, viruses, or other foreign particles
