Structure of carbohydrates – Carbohydrates are a group of organic compounds that occur in living tissues and food, in the form of cellulose, starch and sugars. In carbohydrates, the ratio of oxygen and hydrogen is the same as in water, namely 2:1. Normally, carbohydrates are “broken down” in the body to release energy.
What Are Carbohydrates In Science?
The terms carbohydrate or carbon hydrate come from its basic elemental formula, in which carbon combines with hydrogen and oxygen present in the same ratio as in water. Carbohydrates are chemically polyhydroxy aldehydes or ketones, their simple derivatives or polymers.
Carbohydrates in grains are classified according to their chemical structure or their digestibility when consumed by humans as food or by livestock as feed. Sweet, water-soluble simple carbohydrates are also known as sugars or disaccharides and most sugars end in -ose.
So, we can call ordinary sugar sucrose, while the main sugar in the blood is called glucose and malt sugar is called maltose.
Carbohydrate Structure
Historically, carbohydrates were defined as substances with the empirical formula Cn(HO)m. Common sugars such as glucose and fructose or sucrose fit into this formula, but current convention considers carbohydrates to be polyhydroxy aldehydes or polyhydroxy ketones with the classical formula, molecules closely related to them, oligomers, or polymers of such molecules.
The study developed as a separate subdiscipline within organic chemistry for practical reasons. They are water soluble and difficult to crystallize, so their manipulation requires a different skill than classic “natural products” such as terpenes, steroids, alkaloids, and so on.
Derivatives of carbohydrates that have a single carbon chain are referred to as “monosaccharides”. Meanwhile, the terms “disaccharides” and “trisaccharides” refer to molecules that have two to three monosaccharide units held together by acetal or ketal bonds.
“Oligosaccharides” and “polysaccharides” refer to larger aggregates, with “few” and many monosaccharide units, respectively. Current usage seems to draw the distinction between “a little” and a lot at around 10 units.
By the mid-19th century, a number of relatively pure carbohydrates such as sucrose, cellulose from cotton, starch, glucose, fructose, mannose, and lactose were known to European chemists, particularly in Germany.
Emil Fischer in 1878, synthesized phenylhydrazine for a thesis he was working on at the University of Munich. In 1884, he further discovered that carbohydrates give a phenylosezone crystal in which two phenyl hydrazine react with an aldehyde group and a carbon adjacent to the aldehyde group.
Carbohydrate Formula
Carbohydrates are large macromolecules consisting of carbon (C), hydrogen (H) and oxygen (O). The general formula for carbohydrates is Cx(H2O)y. Carbohydrates are also known as carbon hydrates.
Carbohydrates contain oxygen and hydrogen in the same proportions as those in water. It should be noted, there are some carbohydrates that do not conform to the general formula, such as 2-deoxyribose C5H10O4. Even so, most carbohydrates conform to a general formula.
Carbohydrates are also called sugars. In general, several partially methylated sugars, naturally occurring amino sugars and one naturally occurring nitro sugar are known. All carbohydrates are polyhydroxy aldehydes, ketones, or other substances that produce them on hydrolysis.
The Haworth projection represents the cyclic structure of a monosaccharide. Monosaccharides contain an aldehyde (aldose) or ketone (ketose) group and some -OH groups. The straight chains of cyclized sugars form in solution to form ring structures containing ether bonds.
Glycosidic bonds are formed between monosaccharides to form disaccharides and polysaccharides.
Carbohydrate Source
We know carbohydrates are an important part of the human diet. Some common sources of carbohydrates are:
- Potato
- Labyrinth
- milk
- Popcorn
- Bread
Carbohydrate Classification
The following is a classification of carbohydrates that can increase our understanding, Sinaumed’s.
Simple Carbohydrates
Simple carbohydrates are the basic type of carbohydrates. Soft drinks, candy, cakes and other sweet treats contain simple carbohydrates. These foods are often made with white sugar, a form of refined sugar.
Simple carbohydrates are also found in natural sugars. Fruit, milk and vegetables contain natural sugars. Honey is also a natural sugar. People eat natural sugar in its natural form.
Simple carbohydrates are easier to work with because they are less complex (or simpler). They come from fruit and sugar, as well as almost anything else that’s sweet. The human body can quickly break down these things, and therein lies some of the problems.
There is only one sugar unit in monosaccharides, so they are the smallest carbohydrates. Because of the small size of monosaccharides, they have a special role in digestion and metabolism.
(The prefix “mono-” means “one.) Before they can be digested into the digestive tract, dietary carbohydrates must be broken down into monosaccharides and also travel as monosaccharides in the blood.
Types of Complex Carbohydrates
An important source of energy for our body is complex carbohydrates. They provide the sustainable fuel our bodies need for exercise, daily activities, and even rest.
Complex carbohydrates are often single units (monosaccharides), bonded together. Oligosaccharides contain from two to ten simple sugar units. Meanwhile, Polysaccharides contain hundreds and thousands of linked monosaccharides. Complex carbohydrates themselves have a fairly long lasting energy.
Different types of carbohydrates can be classified based on their behavior in hydrolysis. They are mainly classified into three groups:
- Monosaccharides
- Disaccharides
- Polysaccharides
1. Monosaccharides
Monosaccharides are carbohydrates that can no longer be hydrolyzed further to yield simpler ketone units or polyhydroxy aldehydes. Meanwhile, monosaccharides that contain an aldehyde group are called aldoses, and those that contain ketones are called ketoses.
Structure of Carbohydrates – Glucose
One of the most important monosaccharides is glucose. The two commonly used methods for the manufacture of glucose are as follows:
- From Sucrose : We will get glucose and fructose if sucrose is boiled in dilute acid in an alcoholic solution.
- From Starch : We can obtain glucose by hydrolysis of starch and by boiling it with dilute H 2 SO 4 at 393K under high pressure.
Glucose is also called aldohexose and dextrose, and these are abundant in the earth. Glucose is named as D(+)-glucose, D represents the configuration whereas (+) represents the dextrorotatory nature of the molecule.
The ring structure of glucose can explain many properties of glucose that cannot be described by the open chain structure. The two cyclic structures differ in the configuration of the hydroxyl group on C1 which is called the anomeric carbon. Such isomers i.e. α and β forms are known as anomers. The cyclic structure is also called a pyranose structure because of its analogy with pyran.
The following is the cyclic structure of glucose:
Structure of Carbohydrates – Fructose
It is an essential ketohexose. The molecular formula of fructose is C6H12O6. It contains a ketonic functional group and has six carbon atoms in a straight chain. Members of the fructose ring are analogous to furan compounds and are named furanose. The cyclic structure of fructose is shown below:
Examples of Carbohydrates
Sinaumed’s, here are some examples of products that have the most carbohydrates:
- Dairy Products: Yogurt, milk, and ice cream
- Fruit: Fruit juice or whole fruit
- Grains: Cereals, bread, oats, and rice
- Legumes: Vegetable protein, and nuts
- Starchy Vegetables: Corn and potatoes
2. Disaccharides
- On hydrolysis, disaccharides can produce two molecules of the same or different monosaccharides.
- The two monosaccharide units will be joined by an oxide bond formed by the loss of a water molecule. This relationship is called a glycosidic linkage.
- Sucrose is one of the most common disaccharides which yields fructose and glucose on hydrolysis.
- Maltose and Lactose which are also known as milk sugar, are two other important disaccharides.
- In maltose, there are two α-D-glucose and in lactose, there are two β-D-glucose connected by an oxide bond.
a. Maltose
As a form of disaccharide, maltose is used in fermented or malted milk powder, and in baby food. This type of sugar is the main disaccharide obtained from starch hydrolysis. Maltose is broken down from starch randomly by an enzyme found in saliva, called α-1,4-glucan 4-glucanohydrolase. The enzymes contained in malt specifically convert starch into maltose units.
Malt, in brewing, is also used to convert wheat or other sources into starch or maltose. An enzyme present in yeast (α-glucosidase) catalyzes the hydrolysis of maltose to D-glucose. Then, it is converted into ethanol by other enzymes in the yeast.
Two molecules of D-glucose are produced by one molecule of maltose, whether hydrolysis takes place in an organism, a yeast vat, or a laboratory flask.
b. Cellobiose
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c. Lactose
Milk sugar or lactose is different from cellobiose or maltose. This is because lactose consists of two different simple carbohydrates or monosaccharides, namely D-galactose and D-glucose.
Lactose is a natural disaccharide that can only be found in mammals. There is approximately 5 percent lactose in human and cow milk. Meanwhile, the acquisition of lactose is commercially as a by-product of cheese production.
d. sucrose
In everyday life, sucrose is called cane sugar or granulated sugar. Since 6000 BC, sugarcane has started to be planted in the yard. The Sanskrit word “sarkara” is the origin of the words sucrose and sugar .
Alexander the Great invaded India in 325 BC. He also found cane sugar. After that, through the Arabs and Crusaders, the use of sucrose was spread. Columbus then brought sugar cane to America (Santo Domingo) in 1493.
Certain beets were known to contain high levels of sucrose in the 18th century. This discovery proves that in subtropical regions, sugar can also be obtained from plants.
3. Polysaccharides
- Polysaccharides contain long monosaccharide units held together by glycosidic bonds.
- Most of these polysaccharides act as food storage. For example starch which is the main storage polysaccharide for plants.
- It is a polymer of α glucose and consists of two components, Amylose and Amylopectin.
- Cellulose is also one of the many polysaccharides contained in plants.
- It consists of D-glucose units connected by glycosidic linkages between the C1 of one glucose unit and the C4 of the next glucose unit.
a. Cellulose
Cellulose is the most abundant organic compound on earth. About 1011 tons of cellulose are estimated to be synthesized annually. Cellulose accounts for about 50 percent of the carbon on earth. Dried leaves contain 10-20 percent cellulose, 50 percent wood, and 90 percent cotton. The easiest source of pure cellulose in the laboratory is filter paper.
Cellulose forms a component of plant cell wall fibers. Meanwhile, the toughness of cellulose is caused by its overall structure. Cellulose molecules are chains or chirofibrils of up to 14,000 D-glucose units present as rope-like, twisted bundles held together by hydrogen bonds.
Although mammals do not secrete the proper enzymes to break down cellulose into glucose, certain protozoa and bacteria do secrete these enzymes. Grazing animals use cellulose as food indirectly. Their stomachs and intestines are inhabited by microorganisms that live and reproduce on cellulose, and animals use these microorganisms and their by-products as food.
b. Starch
Starch is the second most abundant polysaccharide after cellulose. Starch can be separated into two main fractions based on solubility when triturated with hot water, which is about 20 percent starch is amylose (soluble), and the remaining 80 percent is amylopectin (insoluble).
Amylose
Complete hydrolysis of amylose produces only D-glucose, while partial hydrolysis produces maltose as the only disaccharide. Amylose was concluded to be a linear polymer of α-D-glucose connected by -1,4′.
The difference between amylose and cellulose is the glycosidic bond, namely β in cellulose and α in amylose. This difference causes the difference in properties between the two polysaccharides.
Amylopectin
Amylopectin is a polysaccharide much larger in size than amylose, containing 1000 or fewer glucose units per molecule. Like the amylose chains, the amylopectin main chain contains 1,4′-α-D-glucose.
Unlike amylose, amylopectin is branched so that there is one glucose end for approximately every 25 glucose units. The bond at the branch point is a 1,6′-α-glycoside bond.
glycogen
Glycogen is a polysaccharide used to store glucose in animals and is primarily stored in the liver and muscles. Glycogen has a structure similar to amylopectin.
Glycogen contains glucose chains attached to 1,4′-α with branches (1,6′-α). The difference between glycogen and amylopectin is that glycogen is more branched than amylopectin.
c. Chitin
The polysaccharide which is the main constituent of animals with many legs (eg crabs and insects) is chitin or chitin . It is estimated that 109 tonnes of chitin are biosynthesized on earth each year.
Chitin is a linear polysaccharide containing β-bonded N-acetyl-D-glucosamine. Chitin produces 2-amino-2-deoxy-D-glucose on hydrolysis. The acetate group is released at the hydrolysis stage. Chitin in nature is bound to non-polysaccharide materials, such as proteins and lipids.
Closing
How about it, Sinaumed’s? Of course, we can know more about carbohydrates and even their molecules. Hopefully all the discussion above is useful for you, Sinaumed’s.
For Sinaumed’s who want book recommendations related to carbohydrates, we suggest trying the books “Biochemistry: Carbohydrate Enzymes and Metabolism for MIPA and Health Students”, “The Evil Carbohydrate Myth”, and “The Keto Diet: Dare to Try the Low Carbohydrate Diet Challenge?” by buying the book at sinaumedia.com .
Being #MoreWithReading means we will know better and be smarter. Indeed, reading anything useful can help us in many different ways, including getting to know carbohydrates more deeply.
Author: Sevilla Nouval Evanda
Reference:
- https://caiherang.com/struktur-molecule-karbohydrate/
- https://byjus.com/chemistry/classification-of-carbohydrates-and-its-structure/#:~:text=Carbohydrates%20are%20large%20macromolecules%20consisting,same%20proportion%20as%20in%20water