biology homework?

Question

which of the following is NOT a characteristic of an ion channel
A.It extends from one side of the cell membrane to the other
B. it may or may not have a gate
C. it is polar, so charged substances, such as ions, can pass through the nonpolar lipid bilayer
D. it allows ions to move against their concentration gradient.

Answer 1

D.

Ion channels are formed of glycoproteins (proteins with sugar molecules attached) that tranverse the cell membrane.
They are formed by aggregation of subunits, each a protein by itself, into a cylindrical configuration that allows a pore, thus forming a kind of tube.

Ions cross thru their channels by electrical potential or concentration differences across the cell membrane, the passage itself does not require metabolic energy expenditure. The energy derives from the chemical forces of diffusion, osmosis, and electrochemical equilibrium.
*There are other types of membrane spanning proteins that move ions against these forces, of course with great energy expenditure, but are not considered channels and are called ion pumps.
These channels are selective of the types of ions it allows to cross. In this sense, ion channels are not only open holes of different diameter, since channels that allow the passage of a certain ion do not allow passage of larger or even smaller ones. The type of ion that is allowed to cross depends on the electrochemical configuration of the protein subunits, especially of the side that faces inside the pore. It is common that a type of ion channel will allow several kinds of ions to cross, specially if they all share the same charge (positive or negative).

Answer 2

I do not know the level of detail in your text or what your instructor has in mind. Here are some comments related to your question:

A. This is true only for gap junctions or ion channels with open gates. If the gate is closed, the channel does not extend from one side to the other.
B. All ion channels have gates with the exception of gap junctions the porins of which are not gated.
C. Ion channels provide a high conducting, hydrophilic pathway across the hydrophobic interior of the membrane. This appears to be true for all ion channels.
D. Substrates moving through passive transport pathways such as ion channels, ALWAYS move down their electrochemical gradient. The electrochemical gradient is a combination of the concentration gradient and electrical gradient. An active pathway can move ions against the electrochemical gradient.

Check out the references below:

Answer 3

c. it is polar, so charged substances such as ions can pass through the non lipid polar bilayer
this is because the channels are for passage of ions and not the lipid bilayer surrounding the channels
also their are many types of ion channels energy dependant and energy independant.
the energy dependant one's can allow ions to move across a conc gradient.
the lipid bilayer does not allow anything other than fatty substances to pass thru , this does not include ions.

Answer 4

D. Think of ion channels as the gates of a dam...they can control water flow but they can't make the water flow upwards. It is a type of passive transport. If it was active transport it would use energy (ATP, a concentation gradient, etc) to make a solute flow against its gradient.

Answer 5

D. It allows ions to move against their concentration gradient.

Answer 6

a true
b false
c true
d false
i think