F5 og F6. Membrantransport og Membranpotentialet

Question 1

make a comparison of ion concentrations inside and outside a typical mammalian cell

Answer 1

Question 2

Draw a glucose Na+ symport that uses the electrochemical Na+ gradient to drive the active import of glucose

Answer 2

Question 3

Draw a typical ion channel that flutuates between closed and open conformations

Answer 3

Question 4

Draw and explain why a typical neuron has a cell body, a single axon, and multiple dendrites

Answer 4

Question 5

draw an electrochemical gradient that has two components and explan your drawing

Answer 5

Question 6

Draw an ion channel that has a selectively filter that controls which inorganic ions it will allow to cross the membrane

Answer 6

Question 7

Draw an animal and plant cell which use a variety of transmembrane pumps to drive the active transport of solutes

Answer 7

Question 8

Explain how cell membranes contain specialized membrane transort proteins that facilitate the passage of selected small, water-soluble molecules

Answer 8

Question 9

show how cells use different tactics to avoid osmotic swelling

Answer 9

Question 10

Show how conformational changes in a transporter mediae the passive transport of a solute such as glucose

Answer 10

Question 11

Draw different types of gated ion channels and show how they respond to different types of stimuli

Answer 11

Question 12

Draw how each cell membrane has its own characteristic set of transporters

Answer 12

Question 13

Draw gradient-driven pumps and show how they can act as symptorts or antiports

Answer 13

Question 14

Show how inorganic ions and small, polar organic molecules can cross a cell membrane through either a transporter or a channel

Answer 14

Question 15

Explain why mechanically-gated ion channels allow us to hear

Answer 15

Question 16

Describe how a patch-clamp recording is used to monitor ion channel activity

Answer 16

Question 17

Show how pumps carry out active transport in three main ways

Answer 17

Question 18

Show how solutes cross membranes by either passive or active transport

Answer 18

Question 19

Show some examples of transmembrane pumps

Answer 19

Question 20

Draw the behavoir of a single ion channel and show how it can be observed using the patch-clamp technique

Answer 20

Question 21

Show how the ca2+ pump in the sarcoplasmic reticulum was the first ATP-driven ion pump to have its three-dimensional structure determined by x-ray crystallography

Answer 21

Question 22

Show how the distribution of ions on either side of a cell membrane gives rise to its membrane potential

Answer 22

Question 23

explain why the k+ concentration gradient and k+ leak channels play major parts in generating the resting membrane potential across the plasma membrane in animal cells

Answer 23

Question 24

Explain why the Na+ pump undergoes a series of conformational changes as it exchanges Na+ ions for K+

Answer 24

Question 25

Explain why the na+ pump uses the energy of ATP hydrolysis to pump NA+ out of animal cells and k+

Answer 25

Question 26

Describe how the nernst equation can be used to calculate the contribution of each ion to the resting potential of the membrane

Answer 26

Question 27

Explain why the rate at which a solute crosses a protein-free, artifical lipid bilayer by simple diffusion depends on its size and solubility

Answer 27

Question 28

Describe how the two types of glucose transporters enable gut epithelial cells to transfer glucose across the epithelial lining of the gut

Answer 28

Question 29

Describe how water molecules diffuse rapidly through aquaporin channels in the plasma membrane of some cells

Answer 29

Question 30

Essential concepts

Answer 30

• The lipid bilayer of cell membranes is highly permeable to small, nonpolar molecules such as oxygen and carbon dioxide and, to a lesser extent, to very small, polar molecules such as water. It is highly impermeable to most large, water-soluble molecules and to all ions.

• Transfer of nutrients, metabolites, and inorganic ions across cell
membranes depends on membrane transport proteins.

• Cell membranes contain a variety of transport proteins that function either as transporters or channels, each responsible for the transfer of a particular type of solute.
• Channel proteins form pores across the lipid bilayer through which solutes can passively diffuse.

• Both transporters and channels can mediate passive transport, in
which an uncharged solute moves spontaneously down its concentration gradient.

• For the passive transport of a charged solute, its electrochemical
gradient determines its direction of movement, rather than its concentration gradient alone.

• Transporters can act as pumps to mediate active transport, in which solutes are moved uphill against their concentration or electrochemical gradients; this process requires energy that is provided by ATP hydrolysis, a downhill flow of Na+ or H+ ions, or sunlight.
• Transporters transfer specific solutes across a membrane by undergoing conformational changes that expose the solute-binding site first on one side of the membrane and then on the other.
• The Na+ pump in the plasma membrane of animal cells is an ATPase; it actively transports Na+ out of the cell and K+ in, maintaining a steep Na+ gradient across the plasma membrane that is used to drive other active transport processes and to convey electrical signals.
• Ion channels allow inorganic ions of appropriate size and charge to cross the membrane. Most are gated and open transiently in response to a specific stimulus.

• Even when activated by a specific stimulus, ion channels do not
remain continuously open: they flicker randomly between open and closed conformations. An activating stimulus increases the proportion of time that the channel spends in the open state.

• The membrane potential is determined by the unequal distribution of charged ions on the two sides of a cell membrane; it is altered when these ions flow through open ion channels in the membrane.

• In most animal cells, the negative value of the resting membrane
potential across the plasma membrane depends mainly on the K+
gradient and the operation of K+-selective leak channels; at this resting potential, the driving force for the movement of K+ across the membrane is almost zero.

• Neurons produce electrical impulses in the form of action potentials, which can travel long distances along an axon without weakening. Action potentials are propagated by voltage-gated Na+ and K+ channels that open sequentially in response to depolarization of the plasma membrane.
• Voltage-gated Ca2+ channels in a nerve terminal couple the arrival of an action potential to neurotransmitter release at a synapse. Transmitter-gated ion channels convert this chemical signal back into an electrical one in the postsynaptic target cell.
• Excitatory neurotransmitters open transmitter-gated cation channels that allow the influx of Na+, which depolarizes the postsynaptic cell’s plasma membrane and encourages the cell to fire an action potential. Inhibitory neurotransmitters open transmitter-gated Cl– channels in the postsynaptic cell’s plasma membrane, making it harder for the membrane to depolarize and fire an action potential.

• Complex sets of nerve cells in the human brain exploit all of the
above mechanisms to make human behaviors possible.