Topic 10 - Cell Membrane Transport Flashcards
What is diffusion?*
The action of particles making their way through a particular solvent randomly.
They do this by randomly colliding and “bouncing” off other particles.
What are the different factors that can influence the rate of flux of particles?*
The rate at which particles move in a given direction is called a flux.
The flux is influenced by:
- The absolute temperature: the higher the temperature the faster the particles move, the lower the temperature the slower they move
- Viscosity
- Particle radius: the smaller the particle radius the faster it moves
What is a solvent?*
A solvent is a substance that dissolves another substance (solute) to form a solution.
What is a solute?*
A solute is a substance that dissolves in a solvent to form a solution.
What is a concentration in regards to solvents and solutes?*
Concentration refers to how much solute is dissolved in a given amount of solvent. It tells us how “strong” or “weak” a solution is.
Ions move from areas of high concentration to areas of low concentration.
What is a concentration gradient and a electrical gradient and how do they interact to influence solute movement?*
A concentration gradient occurs when there is a difference in solute concentration across a membrane. Solutes naturally move from high concentration to low concentration (diffusion) until equilibrium is reached.
An electrical gradient exists when there is a difference in charge across a membrane. Ions (charged particles) are attracted to areas of opposite charge.
The concentration gradient can be countered by the electrical gradient to result in zero net movement and vice versa.
What is the equilibrium potential and how is it calculated?*
The equilibrium potential is how much voltage is needed to counteract its concentration gradient and stop net diffusion.
It is calculated by using the Nernst Equation:
INSERT EQUATION
Describe the differences between the Nernst Equation and the Goldman Equation*
The Nernst Equation is used to calculate the equilibrium potential - the voltage at which the concentrate gradient is matched by the electrical gradient.
The Goldman Equation is used to calculate the membrane potential - the actual voltage inside the cell relative to the outside.
The difference between the two equations is that the Nernst Equation is used for only ONE singular ion, whereas the Goldman equation takes into account ALL the ions within the cell.
What effect does changing the ion permeability have on overall membrane potential?*
The membrane potential is calculated using the Goldman Equation.
If an ion has very low permeability, then it does not have much influence in determining the membrane potential of the cell.
If an ion has very high permeability, it does have a large influence in determining the membrane potential of the cell.
Describe the mechanisms by which particles can move through cell membranes in pores*
Pores: Particles can move through pores in the membrane.
- Some have a mobile portion that can randomly open and close to block the channel.
- The time spent open can be effected by electrical field (voltage-gated channel), molecules that bind to the gate (ligand-gated) or direct mechanical deformation (displacement-sensitive).
How can an ion channel be gated?*
Ligand-gated Channel
- A type of ion channel that opens or closes when a specific molecule (ligand) binds to it
Voltage-gated channel
- An ion channel that opens or closes in response to changes in membrane potential (voltage)
Direct mechanical deformation (desplacement senitive)
- A ion channel that opens by physical force or movement rather than voltage or chemical signals
What is the relationship between the two-state Boltzmann activation….. see ILOS*
What are the factors that determine the net flow of an ion across a membrane?*
The flux/current of a ion is calculated using the Goldman-Hodgkin-Kats (GHK) Current equation.
The factors that determine the net flux are
- Conductance
- The number of channels
- The probability that the channel is open
- The voltage across the membrane
- The valance of the ion
If any of those are zero, then the overall flow is zero.
If the conductance, number of channels, and probability increase, the flux rate also increases.
Describe the mechanisms by which particles can move through cell membranes in carriers*
Carriers are large transmembrane proteins that bind particles and allow them through the membrane in a series of steps.
The carriers help the particles travel through the membrane even i they would not pass through on their own.
Carriers have a “speed limit” in terms of the rate they can transfer particles through. This is different to that of pores who do not have a limit.
Describe the mechanisms by which particles can move through cell membranes in symports and antiports*
Some carriers can bind two or more particles at once. They do not transport their particles until all binding sites are filled.
Symports transfer both particles in the same direction.
Antiports transfer both particles in opposite directions.
Describe the mechanisms by which particles can move through cell membranes in pumps*
A pump is a carrier that requires energy (ATP) to change shape and move the ion with it.
Pumps are able to transfer particles against unfavourable conditions, such as large electric fields or concentration gradients.
