All of us need energy to do our daily work. Without energy our bodies feel weak, and our organs are unable to perform their functions.
We are incapable of doing some of the most basic activities such as walking or eating.
Starch and glycogen – the basics explored
Starch as well as glycogen serve as energy storage. These are basically types of carbohydrates that are found in the living cell.
These are polymeric carbohydrates that are made up by joining glucose monomer units by the different types of glycosidic bonds.
Starch and glycogen, both serves as chemical source of energy and form the structural components of the cell as well.
What is starch? Lets revise our basics again
- Starch is the storage form of energy in plants. The excess of glucose that is produced by the plants, is stored in the insoluble form of starch and fats.
- This starch has a more complex structure than glucose that is produced by the plants.
- The young plants depend on this stored starch into their roots, seeds, as well as fruits, until they find a suitable soil on which they can grow independently.
- Starch is main food component for various plants as well as fruits.
Synthesis of starch – an overview
- The starch in plants is made by first converting glucose 1 – phosphate to ADP-glucose by making use of glucose 1 – phosphate adenyl transferase.
- This process requires energy, which is supplied in the form of ATP – adenosine triphosphate.
- Then ADP- glucose is added to a growing chain of glucose residues via the 1,4-alpha glycosidic bonds, setting free the ADP and forming amylose.
- In green plants, the energy is stored as starch which is packed into semicrystalline granules.
- These semicrystalline granules consist of concentric layers of amylose and amylopectin, which is then made bioavailable to the plants on cellular demand.
- It is synthesized during the day, which is stored as granules and is used as a source of energy during night.
- At the end of the growing season, the starch is accumulated in the twigs of the trees near to the buds.
- The starch is stored in fruits, tubers, seeds, rhizomes to make it available to the plants for the next growing season.
Starch in its pure form is a white colored substance that is odorless and tasteless powder. It is insoluble in cold water as well as alcohol.
What is glycogen? Lets revise our basics again!!
Glycogen is the storage form of energy in mammals. It is the producer of energy for animals and fungi. Excess of glucose is stored in the form of glycogen in our bodies.
Whenever, we need a sudden supply of energy, or when our bodies are deficient in energy the stored glycogen in the liver is broken down to give supply of glucose to the cells.
This process is known as glycogenolysis. In humans, glycogen is stored mainly in the skeletal muscles and liver.
In addition, small amounts of glycogen are also stored in kidneys, white blood cells, red blood cells, brain and the glial cells.
During pregnancy, the uterus also stored certain amount of glycogen to provide nourishment to the embryo.
Glycogen synthesis – an overview
- When a meal rich in carbohydrate or protein is eaten, the level of blood glucose rises, which is an indication for the pancreas to secrete insulin.
- Thereafter, blood glucose enters the liver cells via the portal veins.
- The insulin that is released acts on the liver cells also known as hepatocytes to stimulate the glycogen synthase enzyme for the production of glycogen.
- As insulin and glucose remain plentiful in the circulation, more and more molecules of glucose are added to the chains of glycogen.
- Once the meal is digested, the glucose levels gradually begin to fall and so does the insulin secretion. As a result, the synthesis of glycogen also stops.
- When the body requires energy, the glycogen is broken down and is again converted to glucose. For the breakdown of glycogen, the enzyme glycogen phosphorylase is put to work.
- Glycogen is also known as animal starch that is present in liver cells, stomach as well as muscle cells.
Difference between starch and glycogen explained
Table showing the major differences between starch and glycogen
|Criterion for comparison||Starch||Glycogen|
|Starch is a polymeric carbohydrate that consists of numerous glucose units that are joined together with glycosidic bonds.||Glycogen is a glucose polysaccharide that is present in mammals. It is an important source of stored glucose.|
|Starch is stored form of energy in plants.||Glycogen is the stored form of energy in animals and fungi.|
|The molecular formula of starch is C6H10O5 + H2O||The molecular formula of glycogen is C24H42O21.|
Monomer chains / glycosidic bonds
|Starch is made up of 2 polymers – amylose and amylopectin, where amylose forms linear and coiled chains and amylopectin forms branched chains.||Glycogen is made up of monomer units that form short branched chains. It consists of monomer units called alpha glucose which is held by glycosidic bonds.|
|Starch occurs as grains.||Glycogen occurs as small granules.|
|In plants, excess of starch is converted to cellulose, which helps in production of energy, growth as well as repair of cells.||In humans, excess of glycogen is converted to fat, which is broken down when the body requires energy.|
|Starch has a variable molar mass.||Glycogen has a molar mass of 666.577 g/mol.|
|Starch is commonly found in food grains, roots, vegetables and tubers.||Glycogen is mainly found in liver, but is also stored in the skeletal muscles and brain.|
Understanding the differences in a nutshell
- Starch and glycogen both serve as energy reserves. However, starch is the energy reservoir of plants and glycogen is the energy reservoir of animals and humans.
- Starch is made of two polymers – amylose and amylopectin; whereas glycogen is made up of only one molecule.
- Starch occurs as grains, whereas glycogen occurs as small granules.
- Starch has a variable molar mass; whereas glycogen has a fixed molar mass.