Why do certain hormones, like insulin, need receptor tyrosine kinases to bind to?
1. they are too large.
2. they are hydrophobic.
3. they are nonpolar.
4. they are water soluble.
answers
a) 1 only
b) 1 and 4
c) 1, 3, and 4
d) 2 and 4

The reason that hormones such as insulin require receptor molecules on the cell membrane is due to the large size of the molecules of hormones. The cell membrane is permeable to only a certain size of molecules, and molecules that exceed this size limit must be facilitated when entering the cell. Therefore, the answer is A.

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