20 points on Metabolism and Enzymes

1. All organisms do work in order to do all their daily activities, from repairing damaged tissues to reproduction. To do this, organisms need energy.

2. Metabolism is divided into two categories: Anabolic and catabolic processes.

Anabolic processes break down substances. (e.g. starch breaking down into simple sugars).

Catabolic processes build up substances (e.g. transcription and translation).

3. Energy is categorized into two fundamental types: Kinetic and potential energy

Kinetic energy is the energy that is possessed by moving substances (e.g. heart pumping blood).

Potential energy is the energy stored in a certain form (e.g. ATP storing energy to be released).

4. The First Law of Thermodynamics

“The total amount of energy in the universe is constant. Energy can neither be created nor destroyed but only converted from one form to another. If an object or process gains an amount of energy, it does so at the expense of a loss in energy somewhere else in the universe” (Nelson Biology 12, p. 58).

For example: a roller coaster has all its energy as potential energy at the start. When the ride starts, this energy is converted into kinetic energy and is continuously changing between these two energies until the ride stops.

5. Energy is not readily served in the environment. For example, plants produce energy from the sun by the process of photosynthesis. For human beings, through the process of cellular respiration, we get our energy from glucose which in turn is converted into ATP. ATP releases energy that we use for work.

6. Bond energy is the measurement of the stability of a covalent bond. Through the first law of thermodynamics, an equal amount of the bond energy is needed to break the bond (called the activation energy)

7. These two graphs illustrate the chemical reactions that take place within an organism (changes in potential energy). The reactants go through what is called a transition state by the activation energy. The transition state is when the products of the chemical reaction are produced. The one on the left represents the endothermic reaction and the right diagram represents the exothermic reaction

8. Endothermic versus Exothermic

Endothermic reactions: When the reactants release energy, the energy is absorbed (e.g. ATP releasing energy).

Exothermic reactions: The process in which the reactants release energy and the energy is lost (converted into another form). An example would be combustion.

9. Entropy is a measure of disorder in energy (symbol is S). Entropy increases when disorder increases. This explains why endothermic reactions occur as the products are more unstable than their reactants.

The Second Law of Thermodynamics states that “the entropy of the universe increases with any change that occurs. Mathematically, Delta S > 0” (Nelson Biology 12).

10. Entropy (S) increases when the following happen:

- Solids become liquids, or gases

- Liquids become gases

- A smaller amount of reactants form a larger amount of products

- When decomposition occurs (complex to simple)

- When diffusion or osmosis occur (solutes moving from high concentration to low concentration)

11. Free energy (Gibbs free energy): Energy that can do useful work.

So for exergonic reactions, the reactions are spontaneous and have a decrease in free energy. For endergonic reaction is not spontaneous and have an increase in free energy.

12. All the anabolic and catabolic reactions of metabolism are reversible. When a cell’s reversible reactions reach equilibrium (so zero free energy), it is dead.

13. ATP (Adenosine triphosphate) is the main source of energy for all organisms. It consists of adenine (nitrogenous base), the sugar (5 carbons) which is attached to 3 phosphate groups. ATP goes through hydrolysis to release 31 kJ/mol (in a lab) of free energy (about 54 kJ/mol in a living cell).

14. Redox Reactions: a chemical reaction where atoms transfer electrons to other atoms, in other words it is reduction (gaining electrons) and oxidation (losing electrons). An example would be the transfer of 1 electron of sodium to 1 chlorine to form sodium chloride. Redox reactions are exothermic as they release energy to make a new substance.

15. What are enzymes: Enzymes are protein catalysts that speed up chemical reactions, meaning that the reactants become the products much faster. They are usually tertiary or quaternary strucutures.

16. Enzymes do not affect the change in amount of free energy there is in chemical reactions. It cannot change an endergonic reaction into an exergonic reaction or vice versa. It can only reduce the amount of activation energy that is put into the transition state. This means that chemical reactions will become faster.

17. The reactants of chemical reactions that enzymes catalyze are called substrates. The substrate binds onto a specific site of an enzyme. For example, the substrate amylose is catalyzed by the enzyme amylase to produce maltose. Notice that each substrate has their special enzyme.

18. The area that the substrate attaches to the enzyme is called the active site. When the substrate is attached to the enzyme, the protein actually changes shape to better accommodate the substrate. This protein and reactant combination is called the enzyme-substrate complex.

19. Enzyme inhibition: When a competitive substance takes place of the active site of a non-competitive substance. Competitive inhibitors can block non-competitive inhibitors as they have very similar shapes compared to the non-competitive inhibitors. An example would be oxygen binding to hemoglobin. Oxygen is a non-competitive inhibitor while carbon monoxide is a competitive inhibitor. If one continuously keeps breathing in carbon monoxide, the hemoglobin of the body will only carry carbon monoxide and not oxygen. This results in oxygen not being delivered to all the parts of the body and ultimately death.

20. Applications of Enzymes: There are many uses of enzymes in industrial and commercial industries such as cleaning, cheese making, starch production, wine, pulp and paper and more.

Sources used: Nelson Biology 12