During the process of cellular respiration, glucose is broken down into carbon dioxide and water through a series of endergonic reactions.
These reactions require energy in the form of adenosine triphosphate (ATP) to be carried out. ATP is a nucleotide made of three major components: adenine, thymine, and ribose.
Adenine and thymine are bases, or starting molecules, while ribose is a sugar molecule. When glucose is broken down via glycolysis, ATP is used to transfer a phosphate group from ATP to glucose to break it down into several other compounds.
During the citric acid cycle (also called the Krebs cycle), more ATP is used to convert one compound into another. Finally, in electron transport chain (ETC) facilitated oxidative phosphorylation, even more ATP is used to pump protons out of the cell as hydrogen ions (H+). These actions contribute to producing CO2 and H2O as byproducts.
Definition of an exergonic reaction
A chemical reaction in which energy is released as a result of the reaction is called an exergonic reaction. In other words, the reactants of a chemical compound lose energy as a result of the formation of the products of a chemical compound.
When atoms and molecules interact, they may combine and/or rearrange into new compounds. As these interactions occur, energy is sometimes expended in the process. For example, when hydrogen and oxygen molecules combine to form water, energy is expended as the two separate atoms interact to form a new compound.
Exergonic reactions typically occur at normal temperature and pressure, meaning that they do not require any external sources of heat or pressure to occur. These reactions happen independently due to internal forces within the reactants and products.
Examples of endergonic reactions
Some chemical reactions occur in the opposite direction, called endergonic. These reactions require energy in the form of heat or a substrate such as glucose to proceed.
For example, the reaction that produces ATP from ADP and inorganic phosphate requires energy in the form of a high-energy electron transfer. The enzyme that carries out this reaction captures this energy in the form of a high-energy phosphate group.
The synthesis of fat molecules, or lipids, also requires energy in the form of a high-energy glycerol molecule. The synthesis of amino acids requires energy in the form of ATP.
All these reactions require energy due to their inherent instability. If no external sources of energy are provided, then these reactions will halt. However, if external sources of energy are provided, then these reactions will continue until they reach equilibrium.
Examples of exergonic reactions
Exergonic reactions occur in nature all the time. Some of these reactions are extremely important in our lives, while others are simply interesting to know.
One example of an exergonic reaction is photosynthesis. Plants use light energy, carbon dioxide, and water to create glucose, oxygen, and more energy in the form of ATP. This process takes place inside the cell organelles called chloroplasts.
Another example of an exergonic reaction is respiration. In animals, respiration occurs when oxygen enters the blood stream through lungs or gills and into cells where it combines with glucose to produce ATP. This process creates waste products like CO2 and water that are expelled from the body.
Yet another example of an exergonic reaction is fermentation. In this case, glucose is broken down into ethanol and CO2 via a chemical process that releases energy.
What are the main sources of energy for endergonic reactions?
In most cases, the main source of energy for endergonic reactions is ATP. As mentioned before, ATP is adenosine triphosphate, and it is a nucleotide consisting of a base, ribose, and three phosphate groups.
When ATP gives away a phosphate group, it becomes adenosine diphosphate. The loss of the third phosphate group renders it unable to perform its function as a carrier of chemical energy.
When molecules and/or molecules are broken down during metabolic processes, energy is released. This happens because atoms and/or groups of atoms are being joined together. When this happens, some atoms are able to release energy that was stored within them.
For example, when glucose is broken down into two molecules of pyruvate via glycolysis, some chemical energy is released. This occurs because glucose (a six-carbon atom molecule) is joined with two hydrogen atoms to form two-carbon pyruvate.
What are the main sources of energy for exergonic reactions?
In contrast, organisms use exergonic reactions to produce energy. These reactions require energy, which is taken from the surroundings in the form of ATP.
Enzymes are special proteins that help catalyze (speed up) chemical reactions within a cell. In doing so, they use up ATP and produce an end product that the cell can use.
For example, an enzyme may catalyze the reaction of a sugar with a protein molecule to produce two simpler molecules. The end product of this reaction is something that the cell can then use for energy.
By using up ATP in this way, the enzyme has actually helped to produce energy within the cell. Hence, enzymes are said to be exergonic, meaning that they lead to an outgoing of energy.
How do we measure whether a reaction is endergonic or exergonic?
The term “energy” can refer to a few different things, which can make this term confusing. In general, energy can refer to power, electricity, force, or strength.
Power is the amount of energy that is being used or generated. Electricity is one type of energy that can be harnessed and used. Force is the ability to do work, like move something or alter its structure or shape.
How we determine whether a reaction is an endergonic (requiring energy) or exergonic (giving off energy) reaction depends on how you measure these things.
You measure the amount of chemical reactants that are used up and/or produced in the reaction. If there are more products than reactants, then the reaction is an exergonic reaction. If there are more reactants than products, then the reaction is an endergonic reaction.
Does temperature affect whether a reaction is endergonic or exergonyc?
Yes, temperature affects whether a reaction is endergonic or exergonic. When a reaction requires energy in the form of heat to proceed, it is considered an endergonic reaction.
When a reaction releases energy in the form of heat during its process, it is considered an exergonic reaction. The difference between the two is whether energy is absorbed or released during the process.
When a chemical reaction occurs at constant temperature, the entropy of the universe increases. This means that overall, more systems will become more disordered as this process occurs.
By having more disordered systems (i.e., separated molecules) after the reaction occurs, the entropy of the universe increases. Converseley, if systems are more ordered (i.e., integrated molecules) after the reaction occurs, thenthe entropy oftheuniverse decreases.
What factors affect the balance between endergonic and exergygic reactions in cells?
There are a few factors that affect the balance between endergonic and exergygic reactions in cells. One factor is the concentrations of molecules in a cell.
As concentration increases, molecules have more opportunities to interact with each other, which increases the chance of a reaction occurring.
This is why high concentrations of molecules are typically more likely to result in reaction than low concentrations- there are more molecules for something to happen with!
Since reactions require energy, this helps to reduce the amount of metabolic reactions that take place. By reducing the number of reactions that take place, less energy is expended, which is helpful for times of stress.
Another factor that affects the balance between endergonic and exergygic reactions in cells is temperature. As temperature increases, molecular motion increases as well. More molecular motion leads to more chances for reactions to occur.
