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Cellular Steroidogenesis

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Cellular Steroidogenesis

Postby Dr.Stein » Mon Apr 02, 2007 10:51 am

I need a further explanation about this, and also please correct me if I make a wrong statement here:

The biosynthesis of steroid hormone is started from transporting cholesterol (as lipid droplets) into inner part of mitochondria via StAR. Cholesterol then is converted into pregnenolone, which then move to SER to undergo further modification with some enzyme into appropriate hormone. This process needs SER <--> mitochondria transporatation, thus it is like "steroid volleyball" after the final modification in mitokondria. Then the hormone will be secreted from the cell with mechanism..... (?) I read that the mechanism is "endoplasmacrine" but some scientists doubt about this mechanism.

I am wondering about enzymes in mitochondria. How do these enzymes are produced? It is in the same way as enzymes production on SER, which is synthesized in "regular pathway" via nuclear mRNA translation or?

Thank you for your explanation.
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Postby Dr.Stein » Mon Apr 02, 2007 11:05 am

Well, I already found the answer by myself :D
But I still need more and more information to boost my love to Steroid :lol:

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Re: Cellular Steroidogenesis

Postby Revenged » Tue Apr 03, 2007 11:58 am

Dr.Stein wrote:I need a further explanation about this, and also please correct me if I make a wrong statement here:

The biosynthesis of steroid hormone is started from transporting cholesterol (as lipid droplets) into inner part of mitochondria via StAR. Cholesterol then is converted into pregnenolone, which then move to SER to undergo further modification with some enzyme into appropriate hormone. This process needs SER <--> mitochondria transporatation, thus it is like "steroid volleyball" after the final modification in mitokondria. Then the hormone will be secreted from the cell with mechanism..... (?) I read that the mechanism is "endoplasmacrine" but some scientists doubt about this mechanism.

I am wondering about enzymes in mitochondria. How do these enzymes are produced? It is in the same way as enzymes production on SER, which is synthesized in "regular pathway" via nuclear mRNA translation or?

Thank you for your explanation.


I can't see the diagram you posted but hopefully it looks like the one below...

http://dept.kent.edu/biology/stalvey.htm

The first reaction in this diagram 'Cholesterol -> Pregnenolone' is controlled by the mitochondrial enzyme P450CSCC (CSCC stands for - 'cholesterol side chain clevage')... This is the important rate limiting step in the production of the steroid hormones produced in the adrenal medulla (aldosterone, cortisol, DHEA) and in the sex organs (testosterone, oestrogen)...

It is important to realise how strongly steroidogenesis is controlled by hormones but it is complicated... I have included a post from another forum where i have explained the basics of the biochemistry behind oestrogen production so it is easy to understand...

(look at the fourth post in the following link)...
http://www.thestudentroom.co.uk/showthread.php?t=367971

hope that helps...
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Postby Dr.Stein » Wed Apr 04, 2007 3:15 am

Thank you for your answer. I understand the serial reaction of steroidogenesis, but my question is rather for molecular approach instead of biochemistry. I know precursor, the intermediate hormones, the enzymes, but I wonder the mechanism within the cell, not the converting process.

I just wanted to answer my student's question about the comparison of the biosynthesis of steroid hormones and protein hormones. I try to explain in simple way, and this thread is about to summary the steroidogenesis process fromt he beginning until the final hormone is ready to secrete ;)

Thank you once again :D
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Postby Revenged » Wed Apr 04, 2007 9:25 am

Dr.Stein wrote:I just wanted to answer my student's question about the comparison of the biosynthesis of steroid hormones and protein hormones.


ok... you probably already know this... but anyway...

protein hormones are controlled by the rate of synthesis and the rate of secretion...

whereas steroid hormones are controlled only by the rate of synthesis within the cell... this is because they are lipid soluble and can diffuse freely through the cell membrane (which protein hormones cannot do as they are not lipid soluble)...
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Postby Dr.Stein » Wed Apr 04, 2007 10:21 am

Thank you again ;)

So far I summarize this way:

The biosynthesis of protein hormones are started from protein synthesis, which will generate preprohormone at the first time. Modification in Golgi's body will convert it into prohormone and post-translation will be the final modification before the hormone (active hormone) is ready to secrete out of the cell via excocytosis mechanism into circulation to reach their target.

The biosynthesis of steroid hormones are started from protein synthesis, but these proteine are enzymes which will be sent to mitochondria and SER for steroidogenesis.
Steroidogenesis is started when lipid droplets (ester cholesterol) are transported into mitochondria to undergo side-chain cleavage into pregnenolone. The next step will be called as "steroid volleyball" as steroids will move forward and backward between SER and mitochondria for the presence of key enzymes to finally generate certain steroid hormone. This hormone then will be secrete out of the cell into circulation via endoplasmocrine mechanism to reach their target.

I hope it is good enough :)



Hey, could I join your "Students Room" ? It looks nice! ;)
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Postby Revenged » Thu Apr 05, 2007 12:20 pm

i didn't actually know most of that stuff about steroid production... so that's new to me...

and you can join the student room if you like...
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Postby Dr.Stein » Fri Apr 06, 2007 11:28 am

Yeah, steroid production references is very limit according to my experience. If available, then it 's going to be so complicated. If not, then it is only part per part, which mostly in biochemical process. That's why I needed to read many books and journal and try to summarize in simpler way for students :)
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