Protein Hormones and Cell Membrane interaction

[Sproutie]

Hi all, sorry if this has been asked before but i can't find a thread with the info I'm after. I'm doing an access course at lvl3 (AS/A2) which includes biology and I'm stuck on the following question as part of an assignment I'm to hand in next week.

Q: Suggest an explanation for the fact that sex hormones get into cells while hormones such as insulin remain outside.

I know this is probably a simple thing to find out but I've been trawling google for hours and I've only managed to come up with this so far as an answer to half the question:
sex hormones are a type of lipid and are classed as steroid hormones. Because they are lipids they can diffuse easily through the cell membrane.

can anyone help me with why protein hormones are rejected? I'm thinking that it may be along the lines of the cell does not require any protein as it already has its own or that insulin specifically, does its job from outside the cell and doesn't need to be absorbed by the cell. Unfortunately i can only find very complicated texts about this that go over my head or else simple texts that don't address the problem. any help is much appreciated.

 

[Kushal]

maybe it's got something to do with the phospholipid cell membrane??! the steroids diffuse easily as you said, because they are non polar.

if I'm not wrong, proteins can be polar, and so, cannot enter the polar phospholipid easily... this is high school biology, i don't know if this will help/.

 

[chemisttree]

Uhh, because the questioner doesn't know how insulin works?
(Hint: It's receptor is on the cell surface and it moves into the cell via "[URL pits[/url])

 

[Sproutie]

thanks folks I'll check those out. I'm not sure if it is relevant but question 1 on this assignment was about blood cells. Although the question above is question 3 and doesn't mention blood, that might go to explaining why the insulin stays on the outside? or maybe I'm misunderstanding the question.

 

[Revenged]

the insulin receptor in the cell membrane...

insulin binds to the insulin receptor...

the steriods have there receptors in the nucleus (or sometimes in the cytoplam)...

steroids have to travel through the lipid membranes to reach their receptors

 

[Moonbear]

First, as a reminder to those posting help in this thread...don't give too much of an answer directly! Sproutie needs just enough hints and guidance to help find the answer for himself or herself, not be given the answer.

Sproutie, I do want to take a moment to point out that there is a flaw in the question you have been asked. "Sex hormones" are not all steroids. In fact, most are also proteins (gonadotropin releasing hormone, luteinizing hormone, follicle stimulating hormone, and many you have probably not encountered in your textbooks yet and would only encounter in advanced courses on reproductive biology, such as follistatin and activin). You will not need to know this for an introductory course, and should even pretend you don't know it so as not to get confused on an exam, but even insulin can affect the reproductive system, so might be considered a "sex" hormone.

My point is, the question should have asked why steroid hormones can get into cells while protein hormones cannot pass directly through the plasma membrane.

Now, think about the chemistry of the plasma membrane and the chemistry of proteins vs. steroids. Polarity and hydrophobicity should be considered carefully.

(I will also point out that protein hormones often DO get into cells, but they need help getting there, and start working outside the membrane. Your question is getting at that point of WHY do they need that help and can't diffuse across directly, as steroid hormones can.)

 

[Sproutie]

brilliant, thanks again. I shall look into all these points and let you know whai come up with before i hand it in.