Organisms use molecular atoms of food to make organic molecules of larger size such as DNA (deoxyribonucleic acid), fats (lipids), and proteins, and use the energy in food to propel life processes forward. Cells release energy to make new connections by breaking bonds present in food molecules. Although some of the energy is lost as heat each time when energy is transferred, most of it is stored in newly formed molecules. The photosynthetic process normally initiates the energy flow throughout life, uses various types of energy to convert the solar energy into chemical energy, and to make food. Some carrier molecules retain energy for a short time and transfer it to other molecules quickly. This strategy allows for the controlled release of small amounts of energy. For example, a green pigment found in most plants known as chlorophyll is used in the formation of the chemical energy from the solar energy. When the light energy is absorbed by a molecule of chlorophyll, the excitation of an electron occurs and they “jump” to the higher level of energy. Some small tasks of the cells are derived by the lost energy, like building other molecules or moving ions across membranes. Another important short-term photosynthesis energy carrier is NADPH (Nicotinamide adenine dinucleotide), which stores the chemical energy a little longer, but immediately “use it” to help build sugar. Two of the most important sources of the energy are glucose and adenosine triphosphate, often referred to as ATP.
Glucose is a simple structure of six-carbon carbohydrate sugar. It is found in abundance.
Glucose is mainly manufactured in photosynthesis using energy from the sun by plants and most algae. Carbon dioxide and water are utilized in this process. It is used to make cellulose in cell walls, which is the most common carbohydrate.
In all organisms, glucose is the most important energy source in metabolism. In animals, glucose is stored as glycogen, while in plants it is stored as amylopectin and starch.
In all living organisms, the molecule that carries energy is ATP. It is the chemical energy required by the cell for performing three main types of works:
Chemical energy is needed to transport the necessary substances through the membrane.
Chemical energy is also required to perform metabolic reactions that take place on their own.
The third requirement of ATP is in performing mechanical work.
ATP is not a molecule for storing chemical energy; this is the work of carbohydrates such as glycogen, glucose, and fat. When cells need energy, it is converted into ATP by storage molecules.
ATP then functions as a shuttle and sends energy to places in the cell where the energy-intensive activity takes place.
The structure of ATP is composed of mainly three components- ribose sugar, three phosphate groups arranged in the chain, which is attached to a ribose sugar, and adenine nitrogenous base.
The ATP phosphate tail is the real source of energy . The available energy is present between the phosphates in the bond of ATP and is released during their destruction, which means by the water molecule addition (hydrolysis).
Usually, energy is produced only when external phosphate is removed from ATP. In this case, adenosine diphosphate (ADP) is formed from ATP, where the nucleotide formed has only two phosphate groups.
ATP can control cellular processes by phosphorylation in which the phosphate groups are transferred to other molecules. Special and specific enzymes carry out this transfer in which the ATP energy release is combined with energy needed cellular process.
For obtaining energy, cells constantly degrade ATP. Also there is a continuous synthesis of ATP from phosphate and ADP in the cellular respiration process.
ATP synthase enzyme produces the major part of ATP present in the cell. It transforms phosphate and ADP to ATP. ATP synthase resides in the membrane of cell structures called mitochondria. Enzymes are also found in the chloroplasts in plant cells. In energy metabolism, the cellular role of ATP was discovered in 1941 by Hermann Kalkar and Fritz Albert Lipmann.