What is the chemistry of life?

The field in which the chemical properties, structure, location, and biological processes in the body are studied is the chemistry of life. The term chemistry of life incorporates chemistry in the life processes; the study of life processes comes under biology.

Why is chemistry important to understand life?

The living things contain cells, which are the building blocks, and consume nutrients from the food to produce energy through several biological processes. The cells produce energy-carrying molecules through biological processes, which are macromolecules like proteins, lipids, nucleic acids, and carbohydrates. These molecules are known as biomolecules.

The biomolecules are made up of elements, such as carbon, hydrogen, sulfur, nitrogen, phosphorus, and oxygen. To understand the formation of biomolecules, first, the properties and structure of the chemical elements must be understood.

Elements and Atoms

Elements are chemical substances joined through chemical bonds to form matter (that contains mass and uses space). Elements exhibit physical and chemical properties.

A symbol represents an element, for example, ‘H’ for hydrogen and ‘C’ for carbon. The major elements are carbon, nitrogen, oxygen, and hydrogen that are present in living organisms. There are 118 known elements on the earth, and the naturally occurring elements are 94. 

The chemical properties of the elements are stored in the atom. The atomic nucleus and the electrons combine to form an atom. The atomic nucleus consists of protons with positive charge and neutrons with no charge. The electrons contain a negative charge, and these three are known as subatomic particles of an atom.

The atomic nucleus is present at the center of the atom and is surrounded by the electrons in orbit. The electrons and protons are attracted to each other due to their opposite charges. It helps to maintain the structure of an atom.

Chemical bond

The bonds formed between elements, atoms, or molecules to produce compounds are known as chemical bonds. The breakdown of chemical bonds produces energy in living organisms. The production and utilization of energy maintain the balance of life. There are several types of chemical bonds that define the properties of the chemicals joined by these bonds.

Covalent bond

The atoms share their electrons to form a covalent bond. The molecules formed by this bond are known as covalent molecules. There are two types of covalent bonds: 

Polar covalent bond

• The first type of covalent bond is the polar covalent bond in which the electron sharing is not equal between two atoms.
• The electrons are closer to one atom than the other. It happens when one atom is more electronegative than the other atom. Electronegativity is the ability of the atoms to attract the electrons strongly towards them. 
• The hydrogen bonds are the best example of polar bonds. It is formed between hydrogen and atoms more electronegative than hydrogen, such as nitrogen and oxygen. 
• The hydroxyl group is formed by a hydrogen bond between hydrogen and oxygen. The hydroxyl group can be found in many compounds in biology, including water.

Non-polar covalent bond

• The second type of covalent bond is the non-polar covalent bond, in which the sharing of electrons between the atoms is almost equal.
• The atoms of this bond can either belong to the same element or different elements.
• The molecular structure of the oxygen molecule that enters the body during respiration is formed by the non-polar bond between two oxygen molecules. 
• The molecular structure of methane is formed by the non-polar covalent bond, in which the carbon atom shares its four electrons with the four hydrogen atoms.

Ionic bond

An atom transfers its electrons to another atom to form an ionic bond. The atom that loses its electrons gains the positive charge and is known as a cation. The atom that receives the electrons gains the negative charge and is known as an anion. The ionic bond is formed due to the electrostatic force produced between the positively and negatively charged ions. An ionic bond between sodium and chloride ions produces the molecular structure of common salt, sodium chloride.

Strong and weak chemical bonds in biology

The bonds that form stable compounds and require a great amount of energy to break them are strong chemical bonds. The weak chemical bonds form compounds that require a small amount of energy to break them. The non-polar covalent bonds are the strong chemical bonds, while the hydrogen bonds are the weak bonds. The ionic bonds are the moderate bonds weaker than covalent bonds but stronger than the hydrogen bonds.

The covalent bonds are responsible for making the strand of DNA that does not break down easily. The hydrogen bonds are present between the two strands of DNA in the double-helical DNA structure. The hydrogen bond can be easily broken down during the replication process to separate the two strands of DNA. 

The molecules formed by the ionic or polar bonds are constantly produced in the body, which can be easily degraded due to weak bonds. The constant breakdown and production of these bonds maintain the energy level in the body.

Vital molecules in body

Carbohydrates

The compounds in which carbon atom is combined with other atoms through covalent bonds are organic compounds. The organic compounds made up of carbon, oxygen, and hydrogen atoms are known as carbohydrates. They are also known as sugar molecules. 

The carbohydrates are present in the food to produce energy. The carbohydrates are also present in the cell wall of plant cells and the cell membrane of all living cells. The carbohydrates are divided into three types based on their length of chains.

Monosaccharide

The monosaccharides are carbohydrates that are also known as simple sugars. The number of carbon atoms ranges between three and seven. The sugars with three carbon atoms are known as trioses. Glyceraldehyde is an example of triose sugar. The sugars with five carbon atoms are known as pentoses. Ribose sugar is an example of pentose sugar that is an important component of the molecular structure of RNA. The sugars with six carbon atoms are known as hexoses. Glucose is an example of hexose sugar.

Disaccharide

When a glycoside bond links two monosaccharides, the sugar formed is a disaccharide. The glycosidic bond is formed by the condensation reaction in which the removal of water molecules takes place. Sucrose is a disaccharide formed by the combination of glucose and fructose. The combination of galactose and glucose forms lactose. Another disaccharide is maltose that is formed by the condensation of two glucose molecules.  

Polysaccharide

The carbohydrates that contain several monosaccharides joined together through glycosidic bonds are known as polysaccharides. The polysaccharides can also have branches in their chains. Amylose and amylopectin are the polysaccharides formed from the combination of glucose molecules. Amylopectin has the branching in its chain, while amylose does not have any branching. These polysaccharides join to form a molecule of starch. Glycogen and cellulose are also examples of polysaccharides that are made up of glucose molecules. 

Lipids

Lipids are organic compounds that contain fewer oxygen atoms and more hydrogen and carbon atoms. Lipids are macromolecules that can store energy for a long duration. They are also a component of the cell membrane. They can also act as hormones in the body. 

The triglycerides are the lipids formed by the condensation reaction between glycerol molecules and fatty acids to form an ester bond. The fatty acids are the long chains of carbon and hydrogen atoms. The fatty acids containing no double bond are known as saturated fatty acids, while those containing double bonds are unsaturated fatty acids.

Proteins

The proteins are the biomolecules involved in various functions in the body. They can act as enzymes and hormones to regulate various biological activities. They are also involved in protecting the body from foreign pathogens (antibodies) and the transport of the gaseous molecules (hemoglobin). The proteins are formed by a peptide bond between the amino acids through a condensation reaction. The structure of amino acids contains an amino group (having nitrogen and hydrogen atoms) and a carboxyl group (having carbon, oxygen, and hydrogen atoms).

Nucleic acid

Nucleic acids are the macromolecules responsible for the formation of genetic material in living organisms. The deoxyribonucleic acid (DNA) transfers the information from one generation to the next generation. Ribonucleic acid (RNA) is responsible for converting information stored in DNA into proteins to carry out the biological activities in the body.

The condensation reaction between deoxyribose sugar, a phosphate molecule, and a nitrogenous base gives the molecular structure of the DNA. The molecular structure of the RNA is produced by the condensation reaction between ribose sugar, nitrogenous base, and a phosphate molecule.

Adenosine triphosphate (ATP)

The adenosine triphosphate or ATP is a molecule used as a major energy source in all living cells. The molecular structure of ATP contains a ribose sugar, adenine nitrogenous base, and three molecules of inorganic phosphates. The energy is generated due to the hydrolysis of ATP molecules that release inorganic phosphate molecules. The production of one molecule of ATP involves electrons from the hydrogen atoms through the electron transport chain. The hydrogen ions are separated from the intermediates of the metabolic pathways occurring in the matrix of the mitochondria of the cell.

Common Mistakes

The students may interpret the chemistry of life simply as a part of chemistry. However, the chemistry of life is the study of the chemical properties of the molecules involved in the biological processes in organisms. 

Students may assume that lipids are polymers because most of the macromolecules are found to be polymer. However, lipids are not polymers.

Context and Application

This topic is significant in the professional exams for undergraduate, graduate, and postgraduate courses, especially for the following:

• Bachelor of Science in Biochemistry
• Master of Science in Biochemistry
• Doctorate in Biochemistry

Related Concepts

• Biomolecules
• Metabolism
• Biological Organization

Practice Problems

Q1: Which of the following contains a positive charge?

(a) Neutrons

(b) Electrons

(c) Protons

(d) None of the above

Correct Choice: (d)

Q2: Which of the following macromolecules are not polymers?

(a) Carbohydrates

(b) Proteins

(c) Lipids

(d) Polysaccharide

Correct Choice: (c)

Q3: Select the correct definition of the chemistry of life.

(a) It is the study of chemical compounds used in drugs.

(b) It is the study of biomolecules present in the body.

(c) It is the study of physical compounds used in chemistry.

(d) All of the above statements are correct.

Correct Choice: (b)

Q4: Which of the following molecule is produced by the electron transport chain?

(a) ATP (adenosine triphosphate)

(b) Glucose

(c) ADP (adenosine diphosphate)

(d) Lactose

Correct Choice: (a)

Q5: Which of the following biomolecule is responsible for transferring information to the next generation?

(a) Proteins

(b) Carbohydrates

(c) RNA

(d) DNA

Correct Choice: (d)