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Flashcards in Chapter 4 Deck (26):

What are the categories of membrane transport?

Passive transport and active transport.


What is passive transport?

Passive transport is transport across the membrane that does not require energy. Molecules move across membranes from high energy to low energy. Energy of a solution depends on solute concentration. The more solute, the more energy. Therefore, solutes move passively from areas of high concentration to areas of low concentration


What is active transport?

Active transport is transport of materials across the membrane that requires energy.


How can ion concentration vary in intracellular vs. extracellular solutions?

Charged molecules can’t cross without help of other proteins—no simple diffusion, so ion concentrations don’t eventually even out.


What is driving force?

Driving force is the difference in energy across a membrane. Force pushes from higher to lower energy. Molecules are subject to three types of driving force; Chemical, Electrical, and Electrochemical.


What is the electrical driving force?

The electrical driving force affects charged molecules (Ions). Amount of electrical driving force depends on membrane potential. Membrane potential is a difference in electrical potential or voltage across the plasma membrane


Describe the electrical driving force on different membrane potentials?

With a negative membrane potential:
Electrical driving force on cations is inward, Electrical driving force on anions is outward. Amount of driving force depends on the specific value of the membrane potential and the valence of the permeant ion


What is the electrochemical driving force?

The electrochemical driving force s determined by the combination of the chemical driving force and the electrical driving force. Equilibrium potential of an ion is the membrane potential at which the electrical driving force on the ion is equal and opposite to the chemical driving force. The electrochemical driving force on an ion is set by the difference between the ion’s equilibrium potential and the membrane potential.


The eletrochemical driving force

+55 is the membrane potential of sodium. Both sodium and potassium will follow chemical gradient unless there membrae potential is pulling greater. So to repel sodium the membrane potentials must be greater than +55. For Potassium, to get it come inside the cell against it chemical gradient the chemical gradient must be more than -94. The membrane potential, at ANY time, will always be approaching the equilibrium potential of the MOST permeable ion.


At rest is there more sodium or potassium crossing the gradient?

Potassium must be crossing the membrane more at -70 because the resting membrane potential is -70 which is closer to the membrane potential of K+. At rest there is still sodium crossing because it is not all the way at equilibrium. If Potassium was the only one crossing then the membrane potential would be -94. If they are both equally preamble it would be in the middle.


Describe what happens when the cell is at rest for potassium?

K+ concentrations on the inside of the cell are higher than the outside. At rest, the inside of the cell is negative, relative to the outside.

So, the chemical gradient at rest tends to push K+ outside the cell. But the electrical gradient tends to bring K+ into the cell.

At rest, the chemical gradient for K+ is stronger than the electrical gradient. At equilibrium potential for K+ (-94mV), this is no longer the case.


Describe what happens when the cell is at rest for sodium?

Na+ concentrations are much higher on the outside of the cell than the inside. At rest, the inside of the cell is negative, relative to the outside.

So, at rest, both the chemical and electrical gradients tend to move Na+ into the cell.

At the equilibrium potential for Na+ (+55 mV), this is no longer the case.


What is simple diffusion?

Simple diffusion: movement of molecules as a result of random thermal motion. Molecules freely cross membrane and net movement is down electrochemical gradient
Diffusion is constantly happening but at short distances! If membrane is too thick, diffusion will not happen


What is facilitated diffusion?

In Facilitated diffusion molecules bind to specific protein “carriers” or transporters in the membrane that transport them down their electrochemical gradient.


What is diffusion throught the ion channel?

In Diffusion through ion channels molecules flow through pores in specific protein channels in the membrane down their electrochemical gradient


What is the rate of simple diffusion determined by?

The rate of simple diffusion is determined by the driving force (concentration gradient), Membrane surface area, Membrane permeability including; Lipid solubility, Size and shape of molecules, Temperature, and Membrane thickness.


What is primary active transport?

Primary Active Transport Uses ATP directly to provide energy to move molecules against their electrochemical gradient


What is secondary active transport?

Secondary Active Transport is when one molecule moves passively down its electrochemical gradient to provide energy for another molecule to move up its electrochemical gradient.

Cotransport: Cotransported molecules move in the same direction
Countertransport: Countertransported molecules move in opposite directions


What is endocytosis>

Endocytosis is when large molecule get taken into the cell.


What is pinocytosis?

Pinocytosis is when undissolved dissolvable molecules get taken into the cell


What is receptor-mediated endocytosis?

Receptor-Mediated endocytosis – involves a specific molecule. Binding of a SPECIFIC molecule to a receptor on a membrane, and transport of that molecule into the cell. Many depression medications, such as Prozac, are SSRIs (Selective Serotonin Re-uptake Inhibitors), block receptor-mediated endocytosis in certain neuron so that the serotonin released can be absorbed. Block reuptake in Neuron A, where it is forced to bind to the receptors.


What is osmosis?

Movement of WATER across a membrane from an area of low concentration solute to an area of high concentration solute, diluting it, until there is equal concentration of solute on both sides of the membrane. Always passive transport


What is osmolarity?

Total solute particle concentration of a solution.


What are the characteristics of the plasma membrane?

Small or non polar molecule can freely diffuse across the membrane. Large or polar molecules need carriers proteins to move across membrane. The larges the less likely to cross membrane


What is the sodium potassium pump?

Sodium Potassium Pump: purpose is the maintain the chemical gradient of more Potassium inside than out and more Sodium outside than in
​3 binding sites for Sodium, only 2 for Potassium (uses ATPase); reason why the resting membrane potential is negative!


Describe what happens in hypertonic and hypotonic solutions?

Inside of the cell is hypotonic (less than) to the outside (greater than)
​​Cell loses mass because it loses water; cell will shrivel. If the inside of the cell is hypertonic to the outside; cell increases in mass; cell will swell