What types of hormones are there?
The two major types of hormones are peptide hormones and steroid hormones.
Peptide hormones are, of course, proteins, and because they are such huge molecules with varying polarity, they can't diffuse easily in and out of cells. It sounds like quite an unimportant detail, but in fact it's key to a lot of the way that peptide hormones work. For a start, it means they can be stored in the cell, and they circulate freely in the blood stream. Most importantly, because they can't get in and out of the cell, they are secreted out of a cell into the blood by exocytosis. When they get to the cell they need to affect, they tend to work on receptors on the surface of the cell because they can't get in so easily.
Like many other chemicals that the body uses, peptide hormones tend to start as a prohormone, which means it's like the hormone with a bit extra added on. This means it is a bit heavier (i.e. a higher molecular weight), and it is made in the same place as every other protein - in the rough endoplasmic reticulum. It is then converted into its proper hormone state (by chopping off the parts of the prohormone which aren't needed) in the Golgi apparatus, before being stored in vesicles. Endocrine glands are made up loads of cells, each of which is involved in producing these hormones. A single endocrine cell can have thousands of these vesicles, all ready to be fired off into the blood stream when the time comes.
Steroid hormones are, of course, a bit different. Unsurprisingly, they're made from the same original chemical: cholesterol. We're often told that cholesterol is bad, and in high levels it is - and unfortunately, we often do find that it is too high in people. However it is also an important chemical that the body needs for signalling. Unlike peptide hormones, it can diffuse very easily across cell membranes, which has an important effect on how steroid hormones are managed. For a start, steroid hormones have to be stored as their precursor (cholesterol) to stop them diffusing out and getting lost (or having their effect too early!).
However, perhaps most importantly, they have their effect inside the nucleus of the cell because they can diffuse right in. This means steroid hormones are able to affect the kind of things that the cell is involved in. By controlling the brain of the cell, they are able to activate or inactivate particular sections of DNA or RNA, completely changing what is going on. Very clever!
Even though steroids are very different from peptide hormones, proteins are still important. For a start, in order to get from one point to another, steroid hormones tend to be bound to a specific protein circulating in the blood stream; this often stops the hormone from being active, and it is only when the hormone becomes free at the other end that it is able to have its effect. This is obviously important to make sure the hormone makes it that far! The other way that proteins are important is in the simple manufacture of the steroid hormone in the first place. A series of enzymes are needed to convert cholesterol into a steroid hormone; if one of them is inhibited, the cholesterol may take a different route and become a completely different hormone. This is important, because it shows that if there is a lack of a particular steroid hormone, it may not be a problem with the hormone itself but because of a problem with one of its required enzymes.
The two major types of hormones are peptide hormones and steroid hormones.
Peptide hormones are, of course, proteins, and because they are such huge molecules with varying polarity, they can't diffuse easily in and out of cells. It sounds like quite an unimportant detail, but in fact it's key to a lot of the way that peptide hormones work. For a start, it means they can be stored in the cell, and they circulate freely in the blood stream. Most importantly, because they can't get in and out of the cell, they are secreted out of a cell into the blood by exocytosis. When they get to the cell they need to affect, they tend to work on receptors on the surface of the cell because they can't get in so easily.Like many other chemicals that the body uses, peptide hormones tend to start as a prohormone, which means it's like the hormone with a bit extra added on. This means it is a bit heavier (i.e. a higher molecular weight), and it is made in the same place as every other protein - in the rough endoplasmic reticulum. It is then converted into its proper hormone state (by chopping off the parts of the prohormone which aren't needed) in the Golgi apparatus, before being stored in vesicles. Endocrine glands are made up loads of cells, each of which is involved in producing these hormones. A single endocrine cell can have thousands of these vesicles, all ready to be fired off into the blood stream when the time comes.
Steroid hormones are, of course, a bit different. Unsurprisingly, they're made from the same original chemical: cholesterol. We're often told that cholesterol is bad, and in high levels it is - and unfortunately, we often do find that it is too high in people. However it is also an important chemical that the body needs for signalling. Unlike peptide hormones, it can diffuse very easily across cell membranes, which has an important effect on how steroid hormones are managed. For a start, steroid hormones have to be stored as their precursor (cholesterol) to stop them diffusing out and getting lost (or having their effect too early!).
However, perhaps most importantly, they have their effect inside the nucleus of the cell because they can diffuse right in. This means steroid hormones are able to affect the kind of things that the cell is involved in. By controlling the brain of the cell, they are able to activate or inactivate particular sections of DNA or RNA, completely changing what is going on. Very clever!Even though steroids are very different from peptide hormones, proteins are still important. For a start, in order to get from one point to another, steroid hormones tend to be bound to a specific protein circulating in the blood stream; this often stops the hormone from being active, and it is only when the hormone becomes free at the other end that it is able to have its effect. This is obviously important to make sure the hormone makes it that far! The other way that proteins are important is in the simple manufacture of the steroid hormone in the first place. A series of enzymes are needed to convert cholesterol into a steroid hormone; if one of them is inhibited, the cholesterol may take a different route and become a completely different hormone. This is important, because it shows that if there is a lack of a particular steroid hormone, it may not be a problem with the hormone itself but because of a problem with one of its required enzymes.
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