What are proteins and what do they do?

Proteins are an incredibly important and diverse group of molecules. They’re everywhere, and every living organism needs them to survive. In fact, if you were to take some cells from any organism and remove all the water from them, over 50% of the remaining weight would be protein. There are millions of different proteins, which are all unique in both their form and function.

Types of protein

In humans alone there are estimated to be between 250,000 and one million different proteins. Proteins are incredibly diverse in their properties, which have all been perfectly tailored by evolution to suit the organisms that produce them. For example, proteins have an optimum temperature, where they work most effectively, and become less effective or damaged at temperatures that differ from this.

However, organisms have evolved to produce proteins that operate most effectively at the temperatures they live in, which leads to wildly different optimum temperatures. There are bacteria that live in freezing inhospitable parts of the Antarctic and ones that live in boiling hot springs, and yet both have proteins that can work optimally at the temperatures they find themselves in.

Proteins aren’t just found in nature though, humans have made great use of them too, using them for a great diversity of things, such as clothing, washing laundry and in food production.

What, exactly, are proteins?

They are polymers, which are large molecules that consist of many repeating units. More specifically, they are polypeptides, which is the name for a polymer consisting of amino acids. Amino acids are organic (carbon-containing) molecules that contain two structures known as a carboxyl group and an amino group. There are just 20 different amino acids, and all of the great diversity of proteins is created by combining these 20 together in different combinations.

In animals these amino acids are either created by the body or are obtained from food, with some amino acids, known as essential amino acids, being unable to be created by the body. For humans 9 amino acids are essential, but this number varies among species, for example rats have been shown to have 10. Amino acids are linked together with a bond known as a peptide bond, and form long chains. These chains can vary in length from just a few amino acids to thousands.

Functions of proteins

One function of proteins that is very important for all life on earth is their role as enzymes. Enzymes are a type of protein that help chemical reactions to occur, by speeding up reactions that would otherwise be very slow. Enzymes are found everywhere, in your body, in your food, in the bacteria all around you, in your laundry tablets, in food production, everywhere. They are essential to all forms of life.

Protein Function
nature.com

Why are enzymes so essential?

It’s because they allow essential chemical reactions to occur fast enough for them to be useful to living organisms. Without enzymes, many of the chemical reactions essential to life would occur too slowly to be of any use. Examples of these reactions include digesting food, creating DNA, and the production of energy from glucose, water and oxygen.

Enzymes are also made great use of by humans for all manner of tasks. Many laundry tablets contain enzymes that break down dirt, in a process similar to digestion. They are also used in the production of some foods, such as cheese, which sometimes involves an enzyme called rennet, which is obtained either from the stomachs of calves or from bacteria.

Structure of protein

Proteins are also structurally very important for living organisms. Proteins that are very fibrous are known as structural proteins, and they important to organisms in many ways. They form a protective covering over many parts of the body, such as skin, hair, nails, and scales. Another function of structural proteins is to provide structural support in the spaces between body cells. In animals, this task falls to a protein called collagen.

Structure of protein
Source: nature.com

Collagen is the most abundant protein in the bodies of mammals, which shows just how important this job is. Gelatine, an ingredient in many common foods, such as many sweets, is produced from collagen molecules that have been split up using water, in a process known as hydrolysis. Another common use of structural proteins is to produce silk. Silk is a fibre created from proteins, mainly a protein called fibroin, and is produced by many insect species, as well as by spiders. It is invaluable to the survival of these creatures, being used for a huge array of activities, from travelling and

Collagen is the most abundant protein in the bodies of mammals, which shows just how important this job is. Gelatine, an ingredient in many common foods, such as many sweets, is produced from collagen molecules that have been split up using water, in a process known as hydrolysis. Another common use of structural proteins is to produce silk. Silk is a fibre created from proteins, mainly a protein called fibroin, and is produced by many insect species, as well as by spiders. It is invaluable to the survival of these creatures, being used for a huge array of activities, from travelling and

Silk is a fibre created from proteins, mainly a protein called fibroin, and is produced by many insect species, as well as by spiders. It is invaluable to the survival of these creatures, being used for a huge array of activities, from travelling and protection, to catching and storing prey. An entire industry, the silk industry, has sprung up around this particular protein fibre, and this industry is entirely dependent upon an insect known as the silkworm.

Proteins as hormones

Another task that falls to proteins is their function as hormones. There are 3 main types of hormone, and one of these types is the amino acid derivatives, which, as the name suggests, consist of amino acids. Some of these hormones consist of amino acids bound together into protein molecules. Hormones are very important in regulating the body – they act as messengers between two parts of the body, the hormone gland (which produces the hormones) and the cells with the corresponding hormone receptors, which detect the hormone.

A number of essential hormones are proteins, such as insulin, which controls the level of glucose in the blood – blood sugar, and is what causes that energy crash when you eat too much sugar. To see the importance of this particular protein we need only to look at sufferers of diabetes, who either don’t produce insulin or their cells don’t respond to it. Other proteins that act as hormones include growth hormone, which stimulates growth and cell production, and some of the hormones involved in the menstrual cycle.

A number of essential hormones are proteins, such as insulin, which controls the level of glucose in the blood – blood sugar, and is what causes that energy crash when you eat too much sugar. To see the importance of this particular protein we need only to look at sufferers of diabetes, who either don’t produce insulin or their cells don’t respond to it. Other proteins that act as hormones include growth hormone, which stimulates growth and cell production, and some of the hormones involved in the menstrual cycle.

Proteins as antibodies

Some proteins act as antibodies. Antibodies are an essential component of the immune system, they bind to pathogens such as bacteria and viruses, and this allows other components of the immune system to destroy these pathogens. Antibodies are Y-shaped proteins – they have two arms which end in antigen binding sites, which, as their name suggests, bind to antigens. Antigens are anything that causes an immune response, usually bacteria and viruses.

An antibody has specific antigen binding sites that will bind to only one particular type of antigen, and therefore any specific antibody is useful for only one antigen, for example one particular species of bacteria. It will have no effect on any other antigens, for example a different species of bacteria. This is the premise behind immunisation, it allows the body to learn what antibodies to produce if it becomes infected by a particular antigen. This is achieved through the injection of a dead or weakened form of the antigen, so the body can learn which antibody will bind to that antigen. Then, if that antigen is detected by the immune system in the future, a flood of antibodies can be quickly released to deal with it, before illness occurs.

This is the premise behind immunisation, it allows the body to learn what antibodies to produce if it becomes infected by a particular antigen. This is achieved through the injection of a dead or weakened form of the antigen, so the body can learn which antibody will bind to that antigen. Then, if that antigen is detected by the immune system in the future, a flood of antibodies can be quickly released to deal with it, before illness occurs.

Proteins are also involved in transporting molecules and ions within the body of an organism.

These transport proteins are found in cell membranes, which surround every individual cell. They serve as a sort of bridge between the two sides of the membrane (inside and outside the cell). They can assist molecules and ions to diffuse across the membrane, speeding up the process, or they can be involved in something called active transport. This is where the molecules or ions involved can’t diffuse across the membrane in the necessary direction, as there is too great a concentration of the molecule or ion present on the wrong side of the membrane. In this scenario, active transport is the only way to move the molecules of ions to the necessary side of the membrane (the side with the higher concentration). The transport proteins move the ion or molecule across the cell membrane to where they are needed.

Conclusion

So, as you can see, proteins are fantastically diverse and incredibly important group of molecules, and they are involved in much more than what we give them credit for. They aren’t just found in that post-workout protein shake and they certainly do a lot more than just build muscle.

Without proteins you wouldn’t be reading this right now – the photoreceptive pigments in your eyes, which are what detect light, are proteins. Not that that would matter, because you wouldn’t be alive in the first place. In fact, no life would exist, at least not in any form, we would be familiar with, because the basis of all life – DNA, works by producing proteins. And even if we had somehow still managed to evolve without proteins, human society would be very different – I mean, there would be no cheese! In fact, one particular product of proteins, silk, has shaped history. The silk road, which was a network of trade routes connecting China with many other parts of the world, allowed the interaction of many cultures that would otherwise have never met.

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