The Chemistry of Life

Elements and Their Atoms

In chemistry and physics, an element is a substance that cannot be broken down into a simpler substance by chemical means. A pure element is a substance consisting of a single type of atom, with its chemical properties determined by that atom's atomic number, which is the number of protons in its nucleus. Examples of elements include carbon, oxygen, aluminum, iron, gold, copper, mercury, and lead.

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The Chemistry of Life

The Elements of Life

In biology, the elements of life are the essential building blocks that make up living things. They are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. The first four of these are the most important, as they are used to construct the molecules that are necessary to make up living cells. These elements form the basic building blocks of the major macromolecules of life, including carbohydrates, lipids, nucleic acids and proteins. Carbon is an important element for all living organisms, as it is used to construct the basic building blocks of life, such as carbohydrates, lipids, and nucleic acids. Even the cell membranes are made of proteins. Carbon is also used to construct the energy-rich molecules adenosine triphosphate (ATP) and guanosine triphosphate (GTP). Hydrogen is used to construct the molecules water and organic compounds with carbon. Hydrogen is also used to construct ATP and GTP. Nitrogen is used to construct the basic building blocks of life, such as amino acids, nucleic acids, and proteins. It is also used to construct ATP and GTP. Oxygen is used to construct the basic building blocks of life, such as carbohydrates, lipids, and nucleic acids. It is also used to construct ATP and GTP. Phosphorus is used to construct the basic building blocks of life, such as carbohydrates, lipids, and nucleic acids.

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The Chemistry of Life

Chemical Bonds and Reaction Basics

In chemistry, a chemical bond is a lasting attraction between atoms that enables the formation of chemical compounds. The bond may result from the force of attraction between atoms with opposite charges, or through the sharing of electrons as in the covalent bonds.

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The Chemistry of Life

Life in Aqueous Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as the solvent. The solution is usually a liquid, but can also be a solid, gas, or plasma (ionized gas). The solvent is the non-solvent substance, and the concentration of the solute is expressed as a mass fraction.

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The Chemistry of Life

Carbon Chemistry

Carbon is a chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the solar system, chiefly as carbon dioxide (CO2) or methane (CH4). The very next element is oxygen, making carbon and oxygen the most abundant elements in the universe. The atoms of carbon can bond together in different ways, termed allotropes of carbon. The best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper (hence its name, from the Greek "to write"), while diamond is the hardest naturally occurring material known. Graphite is a very good conductor of heat, while diamond has a low thermal conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivity of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen.

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The Chemistry of Life

Monomers and Polymers

A polymer is a large molecule composed of many repeated subunits. The term was coined in 1833 by Jöns Jacob Berzelius, though the first synthetic polymer was not produced until 1855. Polymers are typically extended chains of many repeated subunits. The length of a polymer is usually many thousands of monomer units. Most natural polymers are biopolymers (e.g. proteins, DNA, and RNA), but many common synthetic polymers are thermosets (e.g. polystyrene and polyvinyl chloride) or thermoplastics (e.g. polyethylene, polypropylene, and polyvinyl alcohol). Polymers are also often referred to as plastics, but that term is ambiguous and sometimes misused.

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The Chemistry of Life

Carbohydrates

In biology, carbohydrates (CHO) are a class of molecules that includes sugars, starch, and cellulose. The term is most common in its sense of "starches", which are polysaccharides, and usually used in cooking and food technology. The term is also used for sugars, as in the term "blood sugar" (glucose), which is the main energy source for many living things. The term "carbohydrate" is sometimes extended to a class of molecules that includes all sugars, and is then called saccharides. This includes polysaccharides, which are long chains of glucose molecules, as well as oligosaccharides, which are chains of several (typically two to ten) molecules of glucose.

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The Chemistry of Life

Proteins

Protein is the main structural material of eukaryotic cells, and it performs a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity. Proteins are also important for the immune response in defending the body against pathogens.

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The Chemistry of Life

Nucleic Acids

DNA (deoxyribonucleic acid) is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. A DNA molecule is a long, two-stranded polymer, composed of two helical strands that wind around each other, linked by base pairs. Each strand is composed of four types of nucleotides, which are interchangeable: adenine (A), cytosine (C), guanine (G) and thymine (T). The strands are chemically joined by the bases attaching to the 1' carbon atom of the sugar of one strand (the phosphate group joined to deoxyribose) to the 3' carbon atom at the next nucleotide. The total amount of DNA in all living cells is estimated to weigh 50 billion tons (50 megatons), or 50 megagrams (50 × 10 g). In contrast, the total mass of the biosphere has been estimated to be as low as 4 × 10 g.

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The Chemistry of Life

Lipids

In biology, lipids comprise a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signaling, and acting as structural components of cell membranes.

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