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Carbohydrates - A Primary Source of Energy | 11th Biochemistry : Chapter 5 : Carbohydrates

Chapter: 11th Biochemistry : Chapter 5 : Carbohydrates

A Primary Source of Energy

Digestion of carbohydrates actually starts in the mouth.

A Primary Source of Energy


Digestion of carbohydrates actually starts in the mouth. Enzymes in saliva begin to break down carbohydrates. The Carbohydrates travel through the esophagus, stomach and enter the small intestine.


In the small intestine, carbohydrates get further broken down into single carbohydrate units called monosaccharide. These single molecules get absorbed across the intestine wall and are sent through the blood stream. Carbohydrate in the blood is in the form of a monosaccharide called glucose. The more carbohydrate eaten at one time, the more glucose is going to be released into the blood after digestion.


Now it is important to note, that fats and proteins can also be burnt to provide energy but fats are only burned if there is non-availability of carbohydrates. When fat is burnt in absence of carbohydrates, toxic compounds like called ketone bodies are produced.


Accumulation of these ketone bodies over long period causes a condition called ‘Ketosis” In this condition, blood becomes unable to carry oxygen properly and this can be fatal. Thus, “one of the important functions of carbohydrate is to help burn fat properly”.


i. As a source of energy:


The main function of carbohydrate is to supply energy for the body processes. A greater part of the energy in the diet (more than 50-80%) is supplied by carbohydrates.


Some of the carbohydrates are immediately utilized by the tissues and the remaining is stored as glycogen in the liver and muscles and some are stored as adipose tissues for future energy needs.


ii. Protein-sparing action:


Carbohydrates are mainly utilized by the body of fulfilling the major part of the energy needs, thus sparing protein for tissue building and repairing. The first physiological demand of the body is the need for energy, which must be satisfied before the nutrients are used for other functions. So, this function of carbohydrates is to spare protein for its body building and repair of tissues.


iii. Essential for Fat Oxidation:


Even though fat yields twice as much as energy as carbohydrate for unit weight, carbohydrate is essential for oxidation of fats. The common expression that ‘fat burns in the fire of carbohydrates’ is used to emphasize that in absence of carbohydrates, fats cannot be oxidised by the body to yield energy. A breakdown product of carbohydrate is essential for the oxidation of acetate, which is the breakdown product of fats.


iv. Role in gastro-intestinal function:


Carbohydrates play an important role in the gastro-intestinal functions of mammals. The digestive system changes carbohydrates into glucose, also known as blood sugar. Some glucose is used for energy and the rest is stored in the liver and muscles for later use. When blood sugar rises, pancreas pumps out more and more insulin, a hormone that tells cells to absorb glucose for energy or storage. As cells absorb wwglucose, blood sugar levels begin to fall, which signals the pancreas to start making glucagon, a hormone that tells the liver to release stored glucose.


v. Carbohydrate functions as Antigen:


Many antigens are glycoproteins (which contain oligosaccharide) in nature and give immunological properties to the blood.


vi. Carbohydrate functions as Hormone:


Many Hormones like FSH (Follicular Stimulating Hormone which takes part in ovulation in females) and LH (Leutinizing Hormone) are glycoprotein and help in reproductive processes.


vii. Carbohydrates provide raw material for industry:


Carbohydrates are an important component of many industries like textile, paper, lacquers and breweries.


viii. Other Functions


Agar is polysaccharide used in culture media, laxative and food.


Cellulose acts as roughage of food. It stimulates peristaltic movement and in the secretion of digestive enzymes.


Hyaluronic acid found between joints acts as synovial fluid and provides frictionless movement.


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