What are carbohydrates? Carbohydrates can be found in a diverse array of foods such as fruits, grains, vegetables, and dairy processed products. They are called carbohydrates because, at the chemical level, they contain carbon, hydrogen, and oxygen. Carbohydrates make up one of the basic food groups which are essential for leading a healthy life.
Carbohydrates are a type of biomolecules, so a brief introduction about them is convenient before explaining carbohydrates in depth.
Biomolecules are substances that are part of all living organisms. They fulfill a series of important functions for the correct operation of each cell. Biomolecules are formed from the six most abundant chemical elements in organisms, which are: carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S).
They are synthesized by living beings through a series of chemical reactions of metabolism. All of them have carbon bases and are grouped as follows:
- Amino acids: they form the basis of proteins and form part of a number of metabolic processes. For example, glutamine, cysteine, among others.
- Proteins: they are the “building bricks” of our cells and participate in various biological processes. Some examples are enzymes, hormones, antibodies, among others.
- Lipids: they are responsible for various functions, among which the reserve of energy for the body stands out.
- Nucleic acids: provide biological information of vital importance for the functioning of organisms. For example, DNA and RNA.
- Vitamins: are responsible for physiological functioning. Vitamin A, vitamin C, vitamin B complex, among others are some examples.
- Carbohydrates: they are an essential source of energy for living beings. For example, glucose, starch, cellulose, among others.
The Molecular Structure of Carbohydrates
Carbohydrates are biological molecules which are made up of carbon, hydrogen, and oxygen in a ratio of approximately one carbon atom to each water molecule. This composition is what gives carbohydrates their name: they are made up of carbon (carbo-) plus water (-hydrate). Carbohydrate chains have different lengths, and depending on this length, they can be categorized into; monosaccharides, disaccharides, and polysaccharides. These three categories are explained below:
Monosaccharides or simple sugars are the simplest carbohydrates; they do not hydrolyze; that is, they do not break down into simpler compounds. They have three to seven carbon atoms, and their empirical formula is (CH2O)n, where n ≥ 3. They are named referring to the number of carbons (3-7) and end with the suffix -ose. The main monosaccharide is glucose, the primary source of energy for cells. They oxidize quickly, turning into acids, which is why they are said to have reducing power.
These are classified according to their functional group (aldehyde or ketone) into aldoses, with an aldehyde group, and ketoses, with a ketone group. Some of them may have a cycled structure. And they are named according to the number of carbons that the molecule has:
- Trioses: three carbons
- Tetrosses: four carbons
- Pentoses: five carbons
- Hexos: six carbons
- Heptoses: seven carbons
Monosaccharides are found in honey and fresh fruits such as grapes, apples, pear, kiwi, and banana.
Disaccharides are a type of carbohydrates formed by the condensation of two monosaccharides through an O-glycosidic bond (with loss of a water molecule). Since it is established in the form of ether, an oxygen atom, being the one that joins each pair of monosaccharides, mono or dicarbonyl, which can also be α or β depending on the -OH hemiacetal.
The molecular formula of disaccharides is C12H22O11. The covalent bond between two monosaccharides causes the elimination of a hydrogen atom from one of the monosaccharides and a hydroxyl group from the other monosaccharide. Together, we can say that a water molecule (H2O) that is released into the environment is eliminated in the reaction.
Disaccharides are found in table sugar (sugar cane and sugar beet) and root vegetables such as beetroot, carrot, and parsnip.
Polysaccharides are polymers whose constituents (their monomers) are monosaccharides, which are repeatedly linked by glycosidic bonds. These compounds have a really high molecular weight, which is dependent on the number of monosaccharide residues or units that participate in their structure. This number is almost always indeterminate, variable within limits, unlike what happens with informative biopolymers, such as DNA or protein polypeptides, which have a fixed number of pieces in their chain, in addition to a specific sequence. They are formed by the joining of a large number of monosaccharides. They fulfill various functions, especially energy and structural reserves.
Polysaccharides can be decomposed, by hydrolysis of the glycosidic bonds between residues, into smaller polysaccharides as well as disaccharides or monosaccharides.
In the formation of each glycosidic bond, there is a “surplus” of a water molecule since these are formed by condensation reactions from the union of monosaccharides by covalent bonds. Likewise, in its breakdown by hydrolysis, a water molecule is added to divide it into multiple monosaccharides so that in a chain made of n monosaccharides, there will be n-1 glycosidic bonds. It is easy to deduce that polysaccharides will almost always respond to the general formula: Cx(H2O)x – 1
Polysaccharides are found in cereal grains, vegetables, fruit, nuts, and legumes such as peas, beans, chickpeas, lentils.
Carbohydrates – Energy For Our Body
Carbohydrates really are an essential part of our diet. Most importantly, they provide energy for the most basic functions of our body, such as moving or thinking, but also for the functions that we do not even notice most of the time. During the digestion process, carbohydrates that consist of more than one type of sugar are broken down into their monosaccharides by digestive enzymes and then directly absorbed, causing a glycemic response.
Cells use glucose as a direct energy source, which is used in muscles, the brain, and other tissues. Some of the carbohydrates cannot be broken down and are fermented by our gut bacteria or pass through the gut unchanged. Carbohydrates also play an essential role in our body’s structure and function, so having them in balance is fundamental to be healthy.