Today we continue with the 2007/2008 3rd Year Undenominated Science Exam Paper Semester I which you can find here Biochemistry Exams - 2007/2008 3rd year Undenominated Science Semester I.
Question 3 Many hormones regulate gene transcription in eukaryotic cells. Explain, using examples, how this is achieved by lipid soluble and lipid insoluble hormones.
This question is easy and I bet you know why it is easy. It is easy because we have already answered this question. It has appeared in the previous paper we have exposed:) To see the answer go here Hormone triggered gene expression.
You only have to mention the difference between water soluble and water insoluble hormones.
Water insoluble - hormones (like the one in the animation here McGraw Hill - Mechanism of Steroid Hormone Action) require protein carriers which are necessary for their transport (remember, blood and cytoplasm are water solutions). Notice that water insoluble hormones do not have any problems with passing through the cell membrane (because their hydrophobic - partially water insoluble).
Of course there are also water insoluble hormones that interact with the membrane receptros on the target cells. Binding to the receptor changes its conformation what leads to signal transduction into the cell, where appropriate gene transcription activators/deactivators are switch on/off.
Either scenario leads to transcription of essential genes and production of proteins, what leads to hormone induced reaction.
Water soluble - hormones do not have any problems with traveling through the blood as they dissolve in it very easily. But they do have problems entering the cell (passing the membrane). As the membrane is highly hydrophobic there is no way water soluble molecule can pass it. In this case water soluble receptors have to interact with the cell surface receptors which transduce the signal further within the cell. Similarly as above appropriate transcription factors are activated what leads to hormone specific response.
Examples:
Water insoluble - cholesterol, estrogen (female hormone), testosteron (male hormone).
Water soluble -epinephrine, dopamine.
To sum up see the picture below:
Picture taken from http://www.biologie.uni-hamburg.de/b-online/library/falk/Endocrine/endocrine.htm
I hope you enjoy it:)
Have a nice day and studying,
Maciek GGSTEAM
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