Every living thing requires energy to survive. Where does this energy come from?

Plants:

Sunlight energy is absorbed by plants, which then store it as proteins, lipids, and carbohydrates.

Animals:

These compounds are ingested by animals in the form of food, which is how they obtain energy from plants.

Human Beings:

Similarly, human beings take energy for the survival of life from plants and animals in the form of carbohydrates, proteins and lipids.

Substances store energy from sunlight:

“Carbohydrates”

What are carbohydrates in biochemistry?

• In biochemistry, carbohydrates in simple words are organic substances that are widely distributed in nature.
• They are aldehyde and ketone monomers and polymers.
• Carbohydrates have the general formula C_n(H₂O)_n, where n is the total number of carbon atoms and is equal to 1, 2, 3, 4, etc.
• Because of this formula, carbohydrates were once thought of as carbon hydrates.

Synthesis of carbohydrates:

• In the presence of sunlight, water, and carbon dioxide, plants are the only living things that can produce carbohydrates in their leafy green coverings.
• Photosynthesis is the term used to describe how plants synthesize carbohydrates.
• The following is a general reaction strategy for the synthesis of carbohydrates:

Glucose (C₆H₁₂O₆):

• This photosynthesis reaction’s result is C₆H₁₂O₆ (Glucose).
• Glucose is polyhydroxy aldehyde (a compound having many hydroxyl groups along with one aldehyde functional group).

Fructose (C₆H₁₂O₆):

• Fructose (C₆H₁₂O₆) is the isomer of glucose.
• Fructose is polyhydroxy ketone (a compound having many hydroxyl groups along with one keto functional group.

“Classification of Carbohydrates”

Carbohydrates are classified into three categories, which are given below:

1. Monosaccharide
2. Oligosaccharide
3. Polysaccharide

Monosaccharide:

• Simple carbohydrates include monosaccharides.
• They have three to six carbon atoms.
• They can no longer be hydrolyzed in water due to their simple nature.
• They often have the formula (CH₂O)_n. where n is the total number of carbon atoms, which can only be 3, 4, 5, or 6.

Classification of monosaccharides:

Monosaccharides are further classified into the following groups according to the number of carbon atoms they contain:

• Trioses (monosaccharides having three C atoms)
• Tetroses (monosaccharides having four C atoms)
• Pentoses (monosaccharides having five C atoms)
• Hexoses (monosaccharides having six C atoms)

Hexoses:

• Fructose (C₆H₁₂O₆) and glucose (C₆H₁₂O₆) are the two hexoses.
• As simple sugars with open chain structures, glucose and fructose are both referred to as monosaccharides.

Dextrorotatory:

Monosaccharides that rotate the plane polarized light clockwise are called dextrorotatory e.g. Glucose, galactose and mannose.

Levorotatory:

Monosaccharides that rotate the plane polarized light anti-clockwise are called levorotatory e.g. Fructose.

2. Oligosaccharide

• Carbohydrates called oligosaccharides have a sweet flavor.
• They can hydrolyze in water and yield 2–10 units of monosaccharides as a result.
• This means that the oligosaccharide will only include the following numbers of carbon atoms: n = 2, 3, 4, 5, 6, 7, 8, and 10.

The following oligosaccharides are further classified according to the number of carbon atoms in them:

• Disaccharides (Oligosaccharides have two C atoms)
• Trisaccharides (Oligosaccharides have  three C atoms)
• Tetrasaccharides (Oligosaccharides have four C atoms)
• Pentasaccharides (Oligosaccharides have five C atoms)
• Hexasaccharides (Oligosaccharides have seven C atoms)
• Heptasaccharides (Oligosaccharides have seven C atoms)
• Octasaccharides (Oligosaccharides have eight C atoms)
• Nonasaccharides (Oligosaccharides have nine C atoms)
• Decasaccharides (Oligosaccharides have ten C atoms)

Disaccharides:

• When disaccharides (oligosaccharides) are hydrolyzed, they break down into two monosaccharides.
• As an illustration, the hydrolysis of the disaccharide sucrose yields two monomers glucose and fructose.
• When lactose (disaccharide) is hydrolyzed, it splits into two monomers glucose and galactose.
• Maltose is a disaccharide that breaks down into two monomers, glucose and glucose. Below are the reaction schemes.

Mechanism for the hydrolysis of Sucrose:

Mechanism for the hydrolysis of Lactose:

Mechanism for the hydrolysis of Maltose:

3. Polysaccharide:

• Carbohydrates with no taste are polysaccharides.
• On hydrolysis, they generate hundreds to thousands of monomers.
• They are insoluble in water, such as cellulose and starch.

“Sources and uses of Carbohydrates”

1. Origins (sources) of Carbohydrates:

Monosaccharides:

Monosaccharides like glucose, fructose, and galactose can be found in plants, fruits, cereals, and honey.

Disaccharides:

Disaccharides like sucrose, lactose, and maltose are present in sugarcane, milk, and oranges correspondingly

Polysaccharides:

Cellulose and starch are polysaccharides, found in plants and animals e.g.

• Cellulose (Cotton)
• Starch (Cereals, barley, wheat, rice, maize and sweet potato)

• Applications (uses) of Carbohydrates:

• Carbohydrates are the source of food for both animals and human beings.
• Our bodies employ carbohydrates to store energy for later use, such as 1g of glucose equals 15.6 kJ.
• A disaccharide called sucrose is used as table sugar.
• Glycogen is the type of glucose that animals store for later use. In the future, if we run out of energy, this glycogen will turn back into glucose and supply our body with energy.
• Starch is the type of glucose that plants store for later use. This starch converts back into glucose when plants in the future experience an energy shortage, giving them the energy they need to survive.
• Starch can be converted into rectified alcohol by the fermentation process.
• Dextrin and wallpaper glue are both adhesives that can be made from starch.
• As a carbohydrate, cellulose is a source of food for termites, cows, goats, and sheep, among other creatures.
• Plants use cellulose as a structural component.

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