Greetings. Welcome to this Principles of Biochemistry lecture series.
I am Jerry Feigenson,
a professor in the Department of Molecular Biology and Genetics
at Cornell University in the USA.
In the previous lecture,
you learned about synthesis of what we could call the most simple lipid, a fatty acid.
Then we saw synthesis of more complex phospholipids and fats.
And we examined cholesterol synthesis in cells. And also how
cholesterol reaches cells after it is packaged into lipoproteins in the liver.
Then we examined synthesis of many nitrogen containing molecules.
In this 22nd lecture,
the final lecture in this series,
you will learn about the different ways,
three or four different ways, that hormones act.
You will see that many hormones work by means of G-proteins.
You will see steroid hormones
that act in the nucleus. And insulin actions,
which are both in the cytosol and in the nucleus.
Then at the very end,
I will give a brief overview of this course.
So hormone action, we can identify four different categories.
The first category, and I will not talk too much about this one,
hormone activated ion channels.
For example, sodium, potassium,
calcium need ion channels,
and these can be hormone activated,
and once activated, the ions get into the cell.
The second category, and the third category,
are peptide or amine hormones that bind to receptors on the outside of cells,
and the action of both of these types is by the receptor,
not by hormone entry into the cell.
I will show you two different kinds of action, two different mechanisms.
In the first mechanism,
the hormone binds to the receptor,
and that receptor changes the transcription of messenger RNAs in the nucleus.
In the second kind of mechanism,
the hormone binds to the receptor and that causes changes in
cytosolic enzymes that already are preexisting in the cell,
but their activity is changed.
Then a fourth category of hormone action,
steroid or thyroid hormones
pass right through the plasma membrane and
usually then right through the nuclear membrane,
and they act on transcription in the nucleus.
That means they alter the amount of newly synthesized mRNA and newly synthesized protein.