208C Membrane Transports Flashcards
Which solutes need transport in eukaryotes?
- Ions
- Glucose
- Amino Acids
Solutes such as ions need a transport system since these charged molecules have to cross the non-polar hydrophobic core of the membrane. Sugars and amino acids and waste products
What are the different types of transport systems?
PASSIVE:
1) Simple diffusion
2) Facilitated transports
ACTIVE:
1) Primary
2) Secondary
What is simple diffusion?
It is a passive transport system that allows non-polar compounds ONLY to be transported down a concentration gradient
Non-polar compounds can cross the hydrophobic core.
Which types of transport are concentration dependent?
Passive transport: simple diffusion and facilitated diffusion. B/c solutes migrate from a region of high concentration to low concentration (down the concentration gradient)
What is facilitated diffusion?
facilitated diffusion uses a pore to transport solutes. The transport is passive and transfer is concentration dependent (down its electrochemical gradient)
How does active transport differ from passive transport?
active transport requires energy b/c transport is against a concentration gradient whereas passive transport does not require energy b/c its down its concentration gradient
What is primary active transport?
free energy provided by the hydrolysis of ATP to ADP helps drive solute against its electrochemical gradient
What is secondary active transport?
movement again is against its gradient but the movement is coupled with the transport of an ion that is moving with the concentration gradient. In this transport method, the spontaneous process (ion transport down its concentration gradient) provides the energy
Which system of transport does not distinguish between passive and active transport?
Uniport = a single solute passes through a pore
CONTRANSPORT EXAMPLE:
Symport: more than 1 solute moving across but the movement of both solutes is in the same direction
Antimport= both solutes move in opposite direction
How can symport/antiport be an example of secondary active transport?
b/c there is movement of 1 solute w/the concentration gradient drives the movement of another solute in the same direction, even if the latter is against its concentration gradient.
Antiport can also be an example except that in this case one of the solutes is moving in the opposite direction
How is a membrane potential generated? What force does it favor and which does it oppose?
when ions of opposite charge are separated by a permeable membrane. This membrane potential produces a force that opposes ion movements that increase the membrane potential, while it favors ion movement that reduce the membrane potential
Movement across a membrane depends on what?
depends upon the concentration (chemical gradient) but also on the electrical (membrane potential) gradient aka electrochemical gradient
What is meant by electreoneutral?
when there is not net change during transport across the membrane
What is electrogenic?
when there is a change in the charge during transport across the membrane aka generates an electrical potential
Why is some passive transport non mediated?
b/c the concentration is the driving force with the solute moving down the gradient. There is no carrier needed. This works provided the solute is non-polar like Co2, O2 and other lipophilic molecules (such as some drugs) can pass right through the membrane.
Can cells regulate passive transport?
cells cannot regulate this type of transport’ it is non-specific and the transport is not saturable
NOTE: that lipophilic molecules in an aqueous solvent result in caging of water, i.e., result in an increase in entropy.
What is meant by mediated passive transport?
this means diffusion is facilitated and a transporter/carrier is required to transport solute although there is still no requirement for an external source of energy. THE DRIVING FORCE IS STILL THE CONCENTRATION GRADIENT
in this type of transport, the solute due to its chemical characteristics cannot easily pass through the membrane. For example, ions, amino acids, and sugars which are hydrophilic in nature will not pass through the hydrophobic core of the membrane. They will require a transporter such as a pore forming protein to facilitate their transport.
How is the free energy requirement of a simple diffusion of a hydrophilic solute in the absence of a transporter? What does the transporter do to this free energy?
The free energy is high. The transporter protein lowers the that activation barrier by forming non-covalent bonds w/the dehydrated solute, thus replacing the hydrogen bonds that the solute would normally form w/water.
In addition, transporters are very specific. Kinetics of facilitated diffusion are similar to enzyme‐catalyzed reactions, including saturation of the transporter‐protein at high solute concentrations.
What are the two types of mediators?
1) pore-facilitated
2) carrier facilitated
What is the difference between pore facilitated and carrier facilitated mediators?
Pore-facilitated = is faster and less specific than carrier facilitated
Pore-facilitated = is relatively temperature-INDEPENDENT, while carrier-facilitated is HIGHLY temperature-DEPENDENT.
Why is carrier-facilitated mediators temperature dependent?
b/c as the temperature increases the membranes become more fluid allow the mediator through
What are two examples of pore-facilitated proteins/channel formers?
1) Porins (beta barrel proteins that re quite large and allow transport of amino acid into the cell
2) Gramicidin A, which is an antibiotic from bacillus brevis, it is helical in shape and can act as an ion channel.
What is the structure of Gramicidin A?
it is a 15mer peptide with both D and L amino acids. It has hydrophobic residues (especially trp) that face towards the outside. It forms a head to head dimer as the foundation of the helical pore and it transports K+ and Na+ but it is blocked by Ca++ b/c it is too big and blocks the pore
Why is Gramicidin A not an alpha helix although it has a helical structure?
b/c an alpha helix does not have a pore down its center and Gramicidin A is a pore
