Question

Lo 10: Electrochemical Gradient

1. The difference in voltage across the membrane is called the __________________________________.

2. The inside of a normal  cell is ___________________ (+/-); while the outside is ___________(+/-).

3. The resting membrane potential of a neuron is  ___________mV.

4. Diagram the relative ratios of Ca++, Na+ and K+ in a cell under resting conditions. Draw an arrow for each of the molecules indicating which direction would be passive transport (into or out of the cell).

5. For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once.

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its __________________ gradient. On the other hand, for a charged molecule, the __________________ must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the __________________ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called __________________ transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) __________________; if the ions move in opposite directions, the transporter is considered a(n) __________________.

antiport                                            coupled                               membrane potential

ATP hydrolysis                                electrochemical                   symport

concentration                                  light-driven                          uniport

6. The action potential is a wave of __________________ that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is __________________ negative than the resting membrane potential. The action potential is propagated by the opening of __________________-gated channels. During an action potential, the membrane potential changes from __________________ to __________________. The action potential travels along the neuron’s __________________ to the nerve terminals. Neurons chiefly receive signals at their highly branched __________________.

anions                                             hyperpolarization               neutral

axon                                                less                                     positive

cytoskeleton                                   ligand                                  pressure

dendrites                                        more                                   synaptic vesicle

depolarization                                negative                              voltage

7. Describe the movement of Na+ and K+ when a Na+/K+ pump is working. Make sure to indicate how many molecules are being transported, which direction they are moving (into or out of the cell), and whether they are moving via active or passive transport.

Answer 1

The difference in voltage across the membrane is called the membrane potential.The inside of a normal  cell is negative ; while the outside is positive.

The resting membrane potential of a neuron is  -70mV.

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its concentration gradient. On the other hand, for a charged molecule, the membrane potential must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the solutes electrochemical gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called coupled transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) symport ; if the ions move in opposite directions, the transporter is considered a(n) antiport.

The action potential is a wave of depolarization,that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is less negative than the resting membrane potential. The action potential is propagated by the opening of voltage -gated channels. During an action potential, the membrane potential changes from negative to positive. The action potential travels along the neuron’s axon to the nerve terminals. Neurons chiefly receive signals at their highly branched dendrites.

Sodium potassium pump.

Active transport is a type of cell transport that requires input of energy in the form of ATP .

The proteins that conduct this form of transport are often called pumps as they force molecules or ions to move from an area of low concentration to an area of high concentration.this is referred to as against the concentration gradient .

One such example is the sodium potassium pump.

Function of sodium potassium pump is to move sodium ions out of the cell and potassium ions into the cell.

Sodium potassium pump has binding sites for three sodium and two potassium ions.After 3 sodium ions are positioned within the carrier protein an ATP molecule is split.This phosphate binds to a location on the exterior of the carrier protein causing the protein to change shape .As the protein changes shape the three sodium ions are released to the other side of the membrane.Two potassium ions position themselves within the carrier protein causing it to undergo another change in shape In the process the phosphate molecule is released .Once the phosphate molecule is released the carrier proteins expels the potassium ions into the interior of the cell.The carrier then resumes its initial shape completing the cycle.

For every 3 sodium ions leaving the cell ,2 potassium ions enter the cell.Since both sodium and potassium has positive charge,this unequal movement causes as electrical gradient to develop across the plasma membrane of the cell.