membrane transport Flashcards
key qualities of cellular membranes
1) semi-permeable (only certain materials can freely cross)
2) selective (membrane proteins regulate the passage)
passive transport
Passive transport involves the movement of material along a concentration gradient (high to low)
does not require energy (ATP) since it moves down a concentration gradient
3 main types of passive transport
1) Simple diffusion (movement of small or lipophilic molecules)
2) Osmosis (movement of water molecules)
3) Facilitated diffusion (movement of large or charged molecules via membrane proteins)
active transpot
active transport involves the movement of materials against a concentration gradient (low to high)
requires energy (ATP) since it moves up the concentration gradient
2 main types of active transport
1) Primary (direct) - involves the direct use of ATP to mediate transport
2) secondary (indirect) - involves coupling the molecule with another moving along an electrochemical gradient
Diffusion
Diffusion is the net movement of molecules from a region of high conentration to a hregion of low concentration. This is passive movement and continued till a balanced equilibrium is achieved. Small and non polar molecules diffuse across membrane easily.
factors influencing rate of diffusion
1) temperature (affects kinetic energy of particles in solution)
2) Molecular size (larger particles create larger resistance)
3) Steepness of gradient (rate of diffisuin increases with higher concentration gradient)
Osmosis
Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.
what role does water play?
Water is considered the universal solvent (associate or dissolve; polar or charged molecules)
Water will move to equalise two solutions aiding them crossing the membrane
Osmosis is essentially the diffusion of free water molecules and occurs from low solute regions concentration
Osmolarity
Osmolarity is a measure of solute concentration as defined by the number of osmoses of a solute per litre of solution
Hypertonic
Solutions with a relatively higher osmolarity are categorised as hypertonic (high solutes = gains water)
Hypotonic
solutions with a relatively lower osmolarity are categorised as hypotonic (low solute = looses water)
Isotonic
solutions that have the same osmolarity are categorised as isotonic (same solute = no net water)
Osmolarity
the osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities
tissues reacting to osmolarity
The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions.
Water loss or gain can be determined with weighing before and after water gain when placed in solution.
Negative effects of uncontrolled osmosis
1) Hypertonic: water will leave the cell causing it to shrivel
2) Hypotonic: water will enter the cell causing it to swell and burst
How to control osmosis
1) Hypertonic: cytoplasm will shrink the the cell wall maintains structure
2) Hypotonic: cytoplasm will expand but be unable to rupture
Facilitated diffusion
facilitated diffusion is the passive movement of molecules across the cell membrane via the aid of a membrane protein
- used by molecules that can’t cross the phospholipid bilayer freely
- aided by two transport proteins: Channel and carrier proteins
Carrier Proteins
1) Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
2) Only bind a specific molecule via an attachement similar to an enzyme substrate interaction
3) Carrier proteins may move molecules against concentration gradients in the precedes of ATP
4) Carrier proteins have a much slower transportation rate then channel proteins
Channel Proteins
1) Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
2) Channel proteins are ion selective and may be gated to regulate the passage of ions in response to stimuli
3) Channel proteins only move molecules along a concentration gradient
4) Channel proteins have a much faster rate of transportation then carrier proteins
Axons of nerve cells
The axons of nerve cells transmit electrical impulses by translocation ions to create a voltage difference between membranes
Sodium potassium cell at rest
At rest the sodium potassium cell expels sodium ions from the nerve cell, while potassium ions are accumulated within
When the neutron fires these ions swap locations via facilitated diffusion through sodium and potassium channels
Potassium Channels
1) integral proteins with a hydrophilic inner pore with which potassium ions may be transported
2) the channel is compromised of four trans membrane subunits, while the inner pore contains a selectivity filter at its narrowest region that restricts passage of alternative ions
3) Potassium channels are typically voltage gated and cycle between an open and closed conformation depending on the transmembrane voltage
Active transport
Active transport uses energy to move molecules against a concentration gradient.
This can be generates by:
1) the direct hydrolysis of ATP (primary)
2) indirectly coupling transport with another molecule (secondary)
