ENERGY AND METABOLISM

What is energy and its types

Every living organism on earth requires energy to stay alive. Energy is the capacity to do work: the ability to move matter in a direction in which it would not move without an imput of energy. The amount of matter may be small or large. Energy exists in many forms, including chemical, electrical, nuclear, heat, light, and mechanical energy. There are two types of mechanical energy: kinetic and potential. The first one is when matter that is moving and performing work. When matter is not actually performing a work, but that has the ability to do so is called potential energy. Also exists chemical energy, is equal to potential energy but in the atoms

Laws of thermodinamics

All organisms survive by transforming energy into another. Energy that can be used to do useful work, is called free energy.

• The first law of thermodinamics: states that energy can be neither created nor destroyed; it can only be changed from oneform into another. Therefore, when energy changes take place within an organism, the energy imput always equals the energy output.
  
• The second law of thermodinamics: this one is related to the fact that when energy is transformed from one type to another some of the energy is converted into heat.

Chemical reactions and metabolism

This ones lead to a chemical change in matter. They can be represented by any chemical equation, for example: 2H2+O2 ---> 2H2O. The two melecules of hidrogen (2H2) and one molecule of oxigen (O2) are called reactants or substrates. The two molecules of water, (2H2O) are called products. All equations are balanced this way, reflecting the fact that chemical reactions do nor destroy or create matter.

Cellular metabolism is the sum of all the reactions that the cell carries out, there are two main types of metabolic reaction: catabolism and anabolism. During catabolism substances break down and release energy. During anabolism, chemical reactions take in energy to synthesise complex molecules from simple molecules. Reactions that liberate more energy than they take in are called exergonic; those that take in more energy than they liberate are called endergonic.

Activation energy

Most molecules are in a relatively stable and require an input of energy to react with each other.

There is an energy barrier to the reaction. The amount of energy required to overcome this barrier and start a reaction is called the activation energy.

Catabolic reactions are exergonic (give out energy) because they have a small activation energy compared with the energy released during the reaction: the reaction products contain less energy than the substrates.

Anabolic reactions are endergonic because their activation energy is greater than the energy released during the reaction. The products of the reaction contain more energy than the reactants, therefore extra energy must be supplied for the reaction to proceed.