Vitamins are chemical compounds that, in order to fulfil their function as catalysts inside the cell (often as constituents of coenzymes or other groups associated with enzymes), must be consumed in trace amounts as part of a healthy diet. Vitamins may be defined as follows: Vitamin needs are very organism-dependent, and insufficient vitamin intake has been linked to a variety of diseases. In young animals, vitamin deficiencies typically result in stunted development, a variety of symptoms the type of which varies on the vitamin, and eventually death.
Although a vitamin is typically characterised as an organic molecule that a human or animal needs to receive from their food in extremely trace amounts, this definition is only partially accurate. Vitamins are actually far more complex than that. The plant kingdom does not produce vitamin A, although the pigment carotene is found in all green plants. Most animals have the ability to convert one molecule of carotene into two molecules of vitamin A. Vitamin A does not occur naturally in plants. The only exceptions to this rule are cats and presumably other predators, who in order to receive the preformed vitamin in their natural environment, they have to consume the tissues of other animals. Niacin, too, is not an absolutely necessary nutrient since most animals (cats, once again, being an exception) are able to generate it from the amino acid tryptophan on their own if there is an abundance of tryptophan beyond what is required for the production of proteins.
The majority of species do not require vitamin D in their diet because they are able to receive an adequate amount from the exposure of their skin to sunlight. This exposure causes a sterol that is already present in dermal tissue to be converted into vitamin D. Vitamin D is not a genuine vitamin. The vitamin is then digested, which results in the formation of a hormone that controls the amount of calcium and phosphate that is absorbed and utilised by the body. Animals such as rodents, which normally have very little exposure to sunlight and forage for food primarily at night, appear to have evolved in such a way as to be able to function without the need for vitamin D as long as their intakes of calcium and phosphate are well-balanced. This is the case provided that their intakes of calcium and phosphate are well-balanced.
Vitamin C, also known as ascorbic acid, is a molecule that is present in the tissues of all species. However, since most species are able to produce vitamin C on their own, vitamin C is not considered a vitamin for these species. People, guinea pigs, and fruit-eating bats are examples of species that are unable to produce their own vitamin C. It is likely that their ancestors lost the capacity to do so during a period of time when their diet contained a lot of ascorbic acid.
The kinds of vitamins that different bacteria require might be very different. On the other hand, some of the strains of bacteria that are present in milk (i.e., Lactobacillus) have lost the capacity to synthesis the B vitamins that they require, despite the fact that many of these bacteria are completely independent of any external sources. Due to this ability, they have shown to be effective in the process of determining the vitamin B content in food extracts. In point of fact, many of the vitamins that belong to this category were found initially as growth factors for bacteria, and only later were they studied on animals and people. In general, the diverse bacterial flora that lives in an animal’s digestive tract is responsible for the synthesis of the B vitamins. As a direct consequence of this, ruminant animals are exempt from the necessity of obtaining them from an external source. On the other hand, it is unknown whether or not hindgut fermenters are able to absorb vitamins from the food that passes through their large intestine. Both rats and rabbits, the nutritional needs of which have been extensively researched, have been found to engage in coprophagy, which is the eating of faecal pellets that are rich in vitamins as a result of bacterial fermentation in the hindgut. Rats and rabbits both have the ability to digest large amounts of food.
The fermentation of bacteria is the sole known source of one of the B vitamins, known as cobalamin or vitamin B12; nevertheless, it is possible to receive this vitamin in a roundabout way by consuming the tissues or milk of animals that have obtained it directly from bacteria. The generalisation that “the animal world depends on the plant kingdom” is thus not entirely accurate because animals depend partially on bacteria for this one vitamin. This particular micronutrient is essential for animal survival.
The interdependence of dietary necessities
We have already discussed how the presence of one mineral nutrient can lower or raise the demand for a different mineral nutrient (see above Inorganic nutrients). Similar correlations may be seen among organic nutrients and can be attributed to a variety of causes, the most prevalent of which are briefly covered in the following paragraphs.
Competition inside the cell for areas capable of absorbing substances
Because the process of nutrient absorption typically involves active transport inside the membranes of cells, an excess of one nutrient (A) might hinder the absorption of another nutrient (B) if the two nutrients share the same pathway of absorption. In these kinds of circumstances, it would appear that a higher level of vitamin B is required. However, B can occasionally be provided in a different form that is transported into the cell by a different channel. This process provides the best explanation for the wide variety of instances of amino acid antagonism, which occurs when the suppression of development caused by one amino acid is counteracted by another amino acid. For instance, under certain conditions, Lactobacillus casei needs both D- and L-alanine. These two forms of the same amino acid differ from one another only in the location of the amino, or NH2, group in the molecule, and the absorption pathway for both of these forms of this amino acid is the same. This species’ development can be inhibited by an excess of D-alanine; however, this inhibition can be eased by either giving extra L-alanine or, more efficiently, by supplying peptides of L-alanine. Providing additional D-alanine has the opposite effect. After entering the cell by a route that is distinct from the one used by the other two types of alanine, the peptides have the potential to be degraded into L-alanine after they have reached their destination. It is possible that the fact that peptides are frequently more efficient than amino acids in encouraging the development of bacteria is at least partially explained by the kinds of relationships shown here.
There is competition inside the cell for different areas of usage.
This event is quite similar to the one that happens when nutrients compete for absorption sites; however, it takes place inside the cell and only between nutrients that are structurally very similar to one another (e.g., leucine and valine; serine and threonine).
Relationships between precursors and products
If tyrosine, which is created from phenylalanine, or cysteine, which is formed from methionine, is given to the diet, the demand for the essential amino acids phenylalanine and methionine is significantly decreased in both rats and humans. The fact that tyrosine and cysteine are both produced in mammals from the amino acids phenylalanine and methionine, respectively, provides an explanation for the links between these two compounds. When the latter amino acids, which are considered products, are provided preformed, the former amino acids, which are considered precursors, are required in lesser quantities. In other species, several examples have been found in which a different nutrient serves as a substitute for a required one because the two nutrients share analogous precursor-product interactions.
alterations in the metabolic pathways that are present inside the cell
Rats that are given diets that are high in fat have a need for thiamin (vitamin B1) that is noticeably lower than rats who are given diets that are heavy in carbohydrates. The utilisation of fat as an energy source is known to bypass a crucial thiamin-dependent step, which is known to be involved in the utilisation of carbohydrates as an energy source (that is, for the formation of ATP). It is presumed that the decreased requirement for thiamin results from the change in metabolic pathways.
It is obvious that two or more distinct creatures growing in close proximity to one another can cause distinct overall changes in the environment. This is due to the fact that various species have unique dietary requirements and metabolic activity. In a well-balanced aquarium, for instance, aquatic plants use light and the waste products that are produced by the animals, such as carbon dioxide, water, and ammonia, to synthesise cell materials and generate oxygen. These, in turn, provide the materials that are essential for the growth of animals. It is normal for microbes to have connections like this; for example, the intermediate or end products of the metabolism of one organism may provide critical nutrients for another organism. Examples of this phenomena, which is known as syntrophism, may be found in the naturally mixed populations that occur in nature. In certain cases, the interaction between the two organisms may be so close as to form nutritional symbiosis, also known as mutualism. Several examples of this phenomenon have been found in yeasts and fungi that require thiamin. Members of one group (group A) synthesised the thiazole component of the thiamin molecule, but they require the pyrimidine portion to be preformed. Members of another group (group B) have the relationship between these two components in the opposite direction. Both types of organisms are able to live when group A and group B are grown together in a medium that does not include thiamin. This is because each organism is able to produce the growth factor that is necessary for its partner, but neither organism can grow alone under these conditions. Therefore, it is common for two or more types of microbes to thrive in environments that would not support the growth of a single species.
These nutritional interrelationships may explain why the nutritionally demanding lactic-acid bacteria and the nutritionally nondemanding coliform bacteria are able to coexist in the digestive tracts of mammals. Coliform bacteria are less demanding of nutrients than lactic-acid bacteria. It is well known that the bacterial flora of the intestinal tract synthesise sufficient amounts of certain vitamins (for example, vitamin K and folic acid), to the point where the detection of deficiency symptoms in rats requires special measures. Additionally, it is well known that the role of rumen bacteria in ruminant animals (for example, cows and sheep) in rendering otherwise indigestible cellulose and other materials available to the host animal is well known. These few examples illustrate that syntrophic interrelationships are common in nature and may contribute significantly to the nutrition of a wide variety of species. Syntrophic interrelationships may be found in a wide variety of ecosystems.
The development of organisms’ dietary needs through time.
About the development of the dietary needs of living beings, very little is understood. The nucleic acids, proteins, carbohydrates, and fats that are found in all living cells are produced by specific reaction sequences from a limited number of smaller compounds. The majority of these smaller compounds are shared by all living organisms and, according to the most recent scientific speculation, were present on Earth long before life first emerged. It is assumed that the earliest forms of life were heterotrophic organisms that required many organic nutrients for growth and that they selected such nutrients from their surroundings. This is because the synthesis of cellular proteins from preformed amino acids requires less complex metabolic organisation and less energy than the synthesis of cellular proteins from carbon dioxide and other precursors. This capacity to synthesise eventually evolved to the point where carbon from carbon dioxide could be used to synthesise organic compounds in some organisms. As the supply of these preformed substances was depleted, it is likely that the organisms developed the ability to synthesise these preformed substances from simpler (precursor) materials that were present in the environment.
It was at this point that the process of autotrophy, in its modern form, became theoretically feasible; in point of fact, autotrophy may have originated as a consequence of the depletion of the supply of preformed organic materials in the environment, which led to the requirement that living things produce their own essential components in order to maintain their own viability. This theory rests on the demonstrable assumption that heterotrophic cells are less complicated than autotrophic cells because certain biosynthetic pathways do not take place in heterotrophic cells, whereas autotrophic cells contain the most complex biosynthetic organisation that can be found in living things. This assumption is implicit in the theory. Following the development of photosynthesis, there was a sudden increase in the availability of a continuously renewed supply of the organic molecules that are required for the growth of heterotrophic cells. It became possible for organisms whose environments provided a constant supply of a particular compound to lose the ability to synthesise that compound and still survive as a result of mutations in their genetic material. This was a possibility for those organisms whose environments provided a constant supply of the compound. The simplification in cellular organisation and the energy saved by using preformed cell components would have given such mutant organisms a competitive advantage over the more complex parents from which they were derived and allowed for the mutation to become stable within the cell type as long as such mutant organisms remained in an environment that supplied the necessary compound. As long as such mutant organisms remained in an environment that supplied the necessary compound. The finding that artificially produced mutant offspring of microorganisms can be readily obtained and may require the presence of one or more preformed organic compounds that the parent microorganisms could synthesise provided support for a theory that states that the needs of modern organisms for essential organic nutrients arose as a result of the loss of synthetic abilities that were present in more complex parent organisms. This theory was supported by the fact that more complex parent organisms lost their ability to produce organic compounds.