Biochemistry

1.1 Matter and element

Teaching Learning Outcome (TLO): Identify the main chemical elements of the human body.

Have you ever heard the quotes “You are what you eat?”.  But do you recall eating some iodine or snacking on selenium? All forms of matter- both living and non-living are made up of a limited number of building blocks called chemical elements. Each of these elements is a substance that cannot be split into simpler substance by ordinary chemical medium. About 60 chemical elements can be found in the body, but what all of them are doing there is still unknown. Scientists believe that about 25 of the known elements are essential to life. The human body functions as a result of a large number of chemical reactions involving compounds of all these elements. In this topic we are going to discuss the chemical elements found in human body.

Matter exists in three states either liquid, solid and gas. Example of solid structure in our body is teeth, cartilage and bones. For liquid- blood and sweats, and oxygen and carbon dioxide in the lungs are the gases that can be found in our body. Let’s see which elements are use to build our body!

            Human have 26 chemical elements present in our body. Among the twenty-six elements, 96% of our body mass are built on by only four elements known as the major elements. These elements are; oxygen, hydrogen, nitrogen and carbon. Eight elements known as the lesser elements contribute about 3.6% of building up the body mass that includes calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), magnesium (Mg) and iron (Fe). The remaining 0.4% of body mass are built by another 14 elements that is present in tiny amount known as the trace element. One example of trace element is iodine needed to make thyroid hormones.

Figure 1 Chemical Elements in the Body

1.2 Atom

TLO: Describe the structure of atoms, ions, molecules, free radicals and compounds

Now, we are diving into a deeper level. For each element, it is made up of atoms. Atom is the smallest unit of matter. Each individual atom is composed of subatomic particle. Only three types of subatomic particle are important for understanding the chemical reactions in the human body; neutron, proton and electrons.

Figure 2 Subatomic Particles. (Source: https://chem.libretexts.org/)

The nucleus of an atom is made up of positively-charged proton (p⁺) and uncharged neutron (n⁰). While the tiny, negatively-charged electron (e^-) surround the nucleus. A region known as the electron shells may be depicted as simple circles around the nucleus. Each shell can hold specific number of electrons.

1.2.2 Ions, molecules, and compounds

From what we have discussed, atoms of the same elements have the same number of protons. Each atoms of the elements have a characteristic way of losing, gaining, or sharing their electrons when interacting with other atoms to achieve stability. The way the electrons behave enable atoms in the body to exist in electrically charged forms called ions, or to combine with each other and form a complex combination called molecules.

                                                                    

                    Figure 5 Illustration showing how two atoms of hydrogen and one oxygen atom forms water molecule.

An atom either loses or gains electrons in order to become an ion. An ion can either be positive or negative charge because it has unequal number of protons and electrons. Ionization is the process of losing or gaining electrons. An ion of atom is symbolized by writing its chemical symbol followed by the number of its positive (⁺) or negative (^-) charges. For example, Na⁺ stands for sodium ion that has 1 positive charge because it has lost 1 electron.

Figure 6 Process of sodium ion and chloride ion forming sodium chloride (NaCl).Source: https://hugotlope.blogspot.com/

When two or more atom shares their electron, they will form a molecule. A molecular formula is a chemical formula indicating the numbers and types of atoms in a molecule. The molecular formula for a molecule of oxygen is O₂. The subscript 2 indicates that the molecule contains two atoms of oxygen. Two or more different kinds of atoms may also form a molecule like in water molecule which is form by two hydrogen atoms and one atom of oxygen (H₂O).

Table 1 showing the chemical formula of the compound found in everyday life.

When a substance contains atoms of two or more different elements they are called a compound. Most of the atoms in the body are joined into compounds. Any molecular species that contain an unpaired electron in their outermost shell and can exist independently is known as free radicals. Having an unpaired electron makes the free radical unstable, highly reactive, and destructive to the nearby molecules. In order to achieve stability, free radical either give up their unpaired electron or take electrons from another molecules. In doing so, free radicals might break apart or cause damage to important body molecules.

Figure 7 Illustration showing unstable free radical trying to forcefully take electrons from a healthy cell. (Source: https://clarityhorizons.wordpress.com/)

Free radicals derived from normal essential metabolic processes in the human body or from external sources such as exposure to x-rays, ozone, cigarette smoking, air pollutants and industrial chemicals. There are several diseases are linked to oxygen-derived free radicals are cancer, atherosclerosis, Alzheimer’s disease, emphysema, diabetes mellitus, cataracts and rheumatoid arthritis.

Figure 8 Illustration of how antioxidants donate its electron to the unstable free radical.