Thinking Beyond Science

Hormones evolved in the simplest of organisms. At some point during evolutionary history a single-celled bacterium secreted a chemical into its surrounding environment. In itself this was not terribly noteworthy: cells excrete chemical waste all the time. On the other hand, what was significant, was that another single celled bacterium responded to that chemical; it started to do something different as a result.

This oversimplifies a sequence of extraordinary evolutionary events that occurred, leading to bacteria using chemical signals to communicate with each other. These chemical signals help to coordinate bacterial activities such as division, secretion of toxins or even organization into large, harmonized groups known as biofilms. They can be used to communicate within the same species, or indeed among different species of bacteria.

As multi-celled organisms evolved, cells maintained this ability to secrete chemicals to help coordinate actions between cells – except that now they were working within the same organism rather than different ones. As a result, all living things – from bacteria to blue whales – use chemical signalling to coordinate cellular actions (although not all of these signals are considered to be hormones).

Human hormones are largely just a variation of more simple chemical signals used by single-celled organisms. As organisms evolve, mutations in the genome can bring about small changes in a hormone’s structure. Although these changes can build up over evolutionary time, aspects of the design are conserved. These conserved structural elements make it possible to trace the molecular origins of a hormone, such as insulin, back to single-celled eukaryotes.

As well as evolving themselves, hormones can drive evolution. Mutations that change how a hormone functions, its structure, how it is transported and received by its target cells can result in significant changes. Especially when you consider that hormones shape every aspect of how an organism looks, functions and interacts with its environment.

Some of these changes may be detrimental to the organism, leading to death or decreased rates of survival, and are therefore naturally eliminated from future generations. Others may offer some type of advantage that sends an organism and its descendants down a new evolutionary path.

WHAT TYPES OF MOLECULES ARE HORMONES?

Hormones are organic molecules (made from atoms) and can therefore be classified by their structure – the basic design elements that they all share. It is the structure of the molecule that hormone receptors recognize and bind to, so it is essential for normal hormone function. The structure also affects how the hormone is transported and how it interacts with its target cells.

PEPTIDE AND PROTEIN HORMONES
The majority of hormones are made up of chains of amino acids (a type of molecule) connected by chemical bonds and known as peptides. A peptide hormone can consist of just three amino acids linked together or of more than one hundred amino acids, also linked together. However, when a chain reaches 30 amino acids or more, they are generally called protein hormones. Some of the amino acids in a chain carry an electrical charge; they can thus be attracted or repelled by other links on the chain.

This causes the chain to ‘kink’ in different ways, just as a chain of magnetized links would. In so doing it creates a 3D structure that is very important to how the protein functions and interacts with other molecules, including receptors. These hormones are often produced in an inactivated (prohormone) form first and are activated when needed.

STEROID HORMONES
The next most common group of hormones are the steroids. These hormones are all made from lipid (fat) – mainly cholesterol. They therefore have a characteristic structure in common, which is a series of carbon rings’. Slight changes to the structures attached to these rings can create a whole new hormone.

AMINES
The third group of hormones, amines, is based on the structure of the amino acid tyrosine, so they are also sometimes called ‘tyrosine derivatives’ or ‘amino acid’ hormones.

FAT LOVERS VS WATER LOVERS
A hormone’s affinity (or aversion) to fat or water affects how it is transported through the blood. It also influences how it interacts with its target cells. Hormones can generally be categorized as being fat lovers/water haters (lipophilic/ hydrophobic) or water lovers/fat haters (hydrophilic/lipophobic).

A hormone’s preference for water or fat is largely dependent on its structure. Steroids, being lipid based, are all fat lovers, while most of the peptide and protein hormones are water lovers. Amine hormones, on the other hand, are divided between the two. Those that are produced by the thyroid, for example, thyroxine, are lipophilic-like steroids, while the remainder are hydrophilic-like peptide and protein hormones.

WHERE THEY WORK
Hormones can also be classified into groups (autocrine, paracrine, endocrine, exocrine) based on where they take action. A single hormone may span two or more categories – for example, it might have autocrine as well as paracrine effects.

More commonly known as pheromones, exocrine hormones cause changes in cells of other organisms, either of the same species or different species. The steroid androstadienone is a pheromone found in male sweat; it causes an increase in levels of cortisol (a hormone released when a person is stressed or excited) among potential suitors.

Source : Meet Your Hormones: Discover the Hidden World of the Chemical Messengers in Your Body by Catherine Whitlock

Goodreads : https://www.goodreads.com/book/show/44765578-meet-your-hormones

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