Glucose: Definition, Function, Structure and Metabolism of this Monosaccharide

Monosaccharides are the most straightforward carbohydrates and are classified according to whether they are derived from aldehyde or ketone.

As well as the number of atoms contained in the molecule.

Hexoses contain six carbon atoms found in food, while pentoses, ribose, and deoxyribose control five carbon atoms produced during food metabolism.

Three common sugars: glucose, galactose, and fructose share the same molecular formula: C6H12O6.

Unique hexoses such as glucose and galactose do not require digestion and can be absorbed directly into the bloodstream.

Because of their six carbon atoms, each is a hexose.

Although all three share the same molecular formula, the arrangement of the atoms differs in each case.


Substances like these three, which have identical molecular formulas but different structural formulas, are structural isomers.


Because glucose is the unit from which starch, cellulose, and glycogen are made, there are probably more glucose groups in nature than any other organic group because of its unique role in biological processes.

It is essential as one of the primary energy sources for living organisms, plants, and animals.

The glucose molecule was first isolated in 1747 by the German chemist Andreas Marggraf, who obtained it from raisins.

The name glucose was first used in 1838 by Jean Dumas at the beginning of the century.

The name “glucose” comes from the Greek and French words for “sweet,” referring to must, the first sweet press of grapes used to make wine.

Emil Fischer investigated the structure and properties of the molecule, winning the Nobel Prize in Chemistry in 1902 for his work.

Nature fuel (function)

Glucose is a ready energy source, as its carbon atoms are easily oxidized to form carbon dioxide, releasing energy in the process.

Glucose is the sugar produced by plants during photosynthesis and circulates in the blood of people and other animals as a source of energy.

However, unlike other hydrocarbon fuels, which are insoluble in water, the numerous OH groups in glucose allow it to quickly bind hydrogen with water molecules, making it highly soluble.

This allows glucose fuel to be easily transported within biological systems, for example, in the bloodstream of animals or the sap of plants.

The average adult has between 5 and 6 grams of glucose in their blood, which will supply the body’s energy needs for only 15 minutes, after which the levels must be replenished from the compounds that have been stored in the body. Liver.

Because glucose is found in ripe fruits, the nectar of flowers, leaves, sap, and blood, over the years, it has been given several common names, such as starch sugar, blood sugar, sugar of grape, and corn sugar.

The systematic name (IUPAC) is -2, 3, 4, 5,6-Pentahydroxyhexanal.

Structure of glucose

Glucose is called a monosaccharide because it is a single unit. Still, it is possible to assemble individual sugar units to form a chain, much like monomer units come together to form a long polymer.

If two units join, a disaccharide is formed, examples of which are maltose or malt sugar, lactose or milk sugar, which is found only in mammalian milk, and sucrose, table sugar, cane sugar, or beet sugar.

It is possible to join three glucose units to form trisaccharides, 4 to produce tetrasaccharides, or a considerable number to make polysaccharides.

These complex carbohydrates are polymers used to store energy and form part of the structural tissues of living organisms.

Because glucose has six carbon atoms, it is classified as a hexose. Specifically, it is an example of aldohexose.

It is a type of monosaccharide or simple sugar. It can be found in linear or cyclical form (most common).

Its simple formula is CH2O, which indicates two hydrogen atoms for every carbon and oxygen atom in the molecule.

The hydrogen and -OH groups can rotate around the carbon atoms in glucose, leading to isomerization.

The D-isomer, D-glucose, is found in nature and is used for cellular respiration in plants and animals.

The L-isomer, L-glucose, is not common in nature, although it can be prepared in a laboratory.

Pure glucose is a white or crystalline powder with a molar mass of 180.16 grams per mole and a 1.54 grams per cubic centimeter density.

The melting point of the solid depends on whether the glucose is in the alpha or beta conformation.

The melting point of α-D-glucose is 146 ° C (295 ° F, 419 K). The melting point of β-D-glucose is 150 ° C (302 ° F, 423 K).

An example is a starch, which is the storage form of glucose used by plants. It is found in granules in its leaves, roots, and seeds.

Natural starches are a mixture of two types of polysaccharides, amylose, and amylopectin.

Amylose is a 1: 4 bond connecting a sizeable straight chain with glucose units.

On the other hand, amylopectin consists of many amylose chains to form a highly branched structure.

Branching occurs every 20 to 24 glucose units and results from a 1: 6 bond between glucose units.


Glycogen is the polymeric molecule used to store glucose in animals.

It represents approximately 5% of the weight of the liver and 0.5% of the importance of the muscles in the body.

The structure of glycogen is similar to amylopectin in that it is a strongly branched molecule that contains linear chains of connected glucose units.

When food is consumed, the glucose resulting from the breakdown of carbohydrates enters the bloodstream.

If a large amount of glucose remained in the blood, the osmotic balance between the blood and the cell’s fluids would be disturbed, and the cells would be damaged.

However, this does not happen, as glucose does not stay in the bloodstream but is converted to glycogen in the liver.

The large, branched glycogen molecule is ideal for storage because it is insoluble and cannot pass through cell membranes.

Glucose has the most stable cyclic form of aldohexoses because almost all of its hydroxy group (-OH) is equatorial. The exception is the hydroxy group on the anomeric carbon.

Glucose is soluble in water, where it forms a colorless solution. It also dissolves in acetic acid but only slightly in alcohol.

When the glucose level in the blood falls from being used in the daily activities of the cells, the glycogen is gradually broken down into glucose units that re-enter the blood to replace what has been consumed.


Cellulose is another glucose polymer found in plant cell walls. More than 50% of the total organic matter in the world is cellulose.

For example, wood is about 50% cellulose, and cotton is almost 100% cellulose.

It is a solid and rigid linear molecule, and these characteristics allow it to be used as the primary structural support for plants.

The glucose units are held tightly together by bonds, but every second glucose unit is flipped this time.

These bonds are called b, 1: 4 bonds and human bodies do not have the enzymes necessary to break this bond.

Therefore, any cellulose we eat passes through the digestive tract undigested and acts as fodder.

However, grass-fed animals, such as cows, can digest cellulose, as they have extra stomachs to hold the grass for long periods while the action of particular bacteria breaks it down.

Blood glucose

The “blood sugar level” is the immediate energy source for cellular respiration.

Glucose, also known as dextrose, is a moderately sweet sugar found in vegetables and fruits.

When the enzyme zymase ferments the glucose in yeast, it forms carbon dioxide and ethyl alcohol.

It is the basic structure that all carbohydrates are ultimately reduced to transport through the bloodstream and used by the body’s cells.

Two different routes are involved in glucose metabolism: anaerobic and anaerobic.

The anaerobic process occurs in the cytoplasm and is only moderately efficient.

The aerobic cycle takes place in the mitochondria and results in the most significant release of energy. As its name implies, however, it requires oxygen.

Glucose metabolism

First, it is essential to note that glucose is the main element of human metabolism.

Organisms use glucose for respiration and fermentation in place of another carbohydrate.

The reason is probably that glucose is less likely to react with amino groups in proteins.

The reaction between carbohydrates and proteins, called glycation, is a natural part of aging and a consequence of some diseases such as diabetes, which affect the functioning of proteins.

In contrast, glucose can be added enzymatically to proteins and lipids through glycosylation, which forms active glycolipids and glycoproteins.

Although with a standard “well balanced” diet, the concentration of glucose in the blood over time is the critical factor to consider in metabolism: accumulation and breakdown of fat.

When the blood has a high glucose concentration for an extended period, the pancreas activates insulin, signaling the cells to consume glucose.

These put them in temporary storage, called glycogen, and put everything else in long-term storage inside the body’s fat or fat cells.

On the other hand, this process is reversed when the blood has a low glucose concentration for a sufficient period.

The pancreas releases a protein called glucagon, glycogen is depleted, a group of other hormones (epinephrine, cortisol, testosterone) enters the system, and triglycerides are extracted from your fat cells and converted into Acetyl Co-A, which is the critical precursor to the process the body uses to generate “energy” – ATP for cells.

So when it comes to digestion, a pivotal process to consider is the absorption of glucose in and through the intestinal wall.

It is important to note that the rate of getting free glucose into the bloodstream is relatively high when glucose is released into the intestinal tube.

Most glucose is obtained through ordinary table sugar, but it is also obtained from the starches in foods such as bread, pasta, corn, and potatoes.

The average glucose concentration in the blood is around 0.1%, but it is much higher in people with diabetes.

When glucose undergoes the oxidation process in the body, this process is called metabolism; in this process, glucose releases products such as carbon dioxide, water, and some nitrogenous compounds, releasing energy that cells need for their essential functions.

Glucose supplies approximately 3.75 kilocalories of energy per gram in the human body.

It is metabolized into carbon dioxide and water, producing energy in the chemical form of ATP.

While necessary for many functions, glucose is essential because it supplies most of the energy for the human brain.

Energy performance can be used for work or to maintain body temperature.

The first step in the breakdown of glucose in all cells is glycolysis, which produces pyruvate, the starting point for all other processes of cellular respiration.