At one time, membrane biologists thought that transport proteins might act by binding a solute molecule or ion on one side of the membrane and then diffusing across the membrane to release the solute molecule on the other side. we now know that this transverse carrier model is almost certainly wrong. suggest two reasons that argue against such a model. one of your reasons should be based on our current understanding of membrane structure and the other on thermodynamic considerations.

drag the terms on the left to the appropriate blanks on the right to complete the sentences. not all terms will be used.



reset

exergonic

hydrophobic

hydrophobic and hydrophilic

probable

endergonic

hydrophilic

improbable

integral membrane proteins are embedded stably in the membrane and protrude from one or both sides based on their regions.

for a protein to traverse a membrane, movement of its region(s) through the interior of the membrane would be required, which would be highly and hence thermodynamically .

The process of passage of different molecules, solutes, and liquids, through the phospholipid bilayer in human cells, and really in all animal cells, is highly dependent on a tight coordination between chemical, and thermodynamic balances, that will collaborate in these elements being able to pass, or not pass, through a cell´s membrane, and activate other mechanisms within the cell when their passage is not possible. Unlike what was once believed, that transport proteins were like buses parked at the membrane and waiting to be loaded with molecules to later remove themselves from the membrane and carry their load into the cytoplasm, scientific research has found that this is definitely so, and that transport proteins do not come off the layer to transport  molecules. They are permanently anchored to the membrane and through a series of second messenger systems, energy produced by the passage of certain ions like potassium and sodium, and other such processes, these transport proteins become activated, allow the passage of molecules and change them in such a way that they can be taken into the cell in vesicles, or, they will anchor them to second messengers, who will be responsible for carrying the molecule inside.

From the list of words given and the two sentences down below, which are two reasons why the earlier believed models for transport proteins are not correct would be:

1. Integral membrane proteins are embedded stably in the membrane and protrude from one or both side based on their hydrophobic, or hydrophilic, regions. These sides will not switch because of the disbalance that would be created if the two sides had to be switched chemically to allow them to pass to the opposie sides.

2. For protein to traverse a membrane, movement of its hydrophilic regions through the interior of the membrane would be required, which would be highly endergonic and hence thermodynamically improbable.

the backbone of the dna and rna compound is sugar phosphate.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands