The bulk of the covalent bonds found in macromolecules have a property that allows the atoms to which they are attached to rotate. This property gives the polymer chain a great amount of flexibility. Due to the fact that random thermal energy causes the polymer chain to twist and turn, macromolecules are theoretically possible to assume an almost limitless number of different shapes, also known as conformations. The majority of biological macromolecules have their geometries severely constrained by the numerous weak noncovalent interactions that occur between the various components of a single molecule. If there are a sufficient number of these noncovalent bonds established, the polymer chain may strongly favor one particular conformation over another. This conformation is determined by the linear arrangement of the monomers that are contained inside the chain. This is how the majority of the teeny RNA molecules and the majority of the protein molecules that are present in cells fold up into a compact and highly desired shape.

Together, they are able to fold biological macromolecules into novel shapes and create a powerful attraction between two molecules. In addition, they can fold biological macromolecules into novel shapes. Because of the multipoint contacts that are required for strong binding, this type of molecular interaction is very specific. This allows a macromolecule to select only one of the thousands of other types of molecules that are present within a cell. Interactions of nearly any affinity are possible due to the fact that the strength of the binding can be regulated by the quantity of noncovalent bonds generated, which in turn enables rapid dissociation whenever it is necessary.

Everything that is alive is a self-replicating system that is chemically autonomous. To a large extent, they are made up of a singular and restricted group of extremely small molecules that are based on carbon and are the same for all living organisms. Every one of these minuscule molecules is constructed from a predetermined amount of atoms that are chemically connected to one another in a predetermined configuration. The primary groups consist of sugars, fatty acids, amino acids, and nucleotides respectively. Sugars, which are the primary source of chemistry-based energy for cells, can be incorporated into polysaccharides, which serve to store energy. Fatty acids are essential for the storage of energy in addition to playing an important part in the formation of cell membranes. Fatty acids serve a key role in the creation of cell membranes. Long sequences of amino acids are what compose proteins, which are remarkable macromolecules due to their high level of complexity and adaptability. Nucleotides are fundamental to the process of transferring energy, in addition to serving as the structural components of the information-carrying macromolecules RNA and DNA.

The bulk of a cell's dry mass is composed of macromolecules that are covalently connected to one another in a specific sequence. These macromolecules originated as linear polymers of amino acids (proteins) or nucleotides and are what make up the majority of a cell (DNA and RNA). The distinctive conformation that the majority of protein molecules and a significant number of RNA molecules fold into is determined by the sequence of their subunits. This folding process, which is dependent on a huge number of weak attractions brought about by noncovalent forces between atoms, results in the production of surfaces that are distinct from one another.

The hydrophobic repulsion of nonpolar groups from water, hydrogen bonds, van der Waals attractions, and electrostatic attractions are all examples of these types of forces. As a result of these forces, nonpolar groups are able to interact with one another. The same set of weak forces that regulate the specific binding of other molecules to macromolecules also make it possible for the diverse associations between biological molecules that result in the structure and chemistry of a cell. These associations are what result in the cell's structure.

One feature of living things in particular makes them appear almost magically separate from nonliving matter in a cosmos that is continuously going toward greater disorder. This is because the universe is always advancing toward more disorder. They are the ones who create and maintain order. In order to maintain this order, the cells of an organism that is still alive are required to carry out an endless chain of chemical reactions. In some of these reactions, small organic molecules such as amino acids, carbohydrates, nucleotides, and lipids are broken down or changed in order to make the myriad of other small molecules that the cell requires. Other mechanisms lead to the manufacture of a vastly extensive variety of macromolecules, such as proteins, nucleic acids, and other types of macromolecules. These macromolecules are what give living systems all of their distinctive qualities. Each each cell can be conceptualized as a miniature chemical factory that is responsible for millions of reactions occurring simultaneously.

The temperatures that are experienced within cells are noticeably lower than those at which the chemical reactions that are taking place would normally take place. Because of this, each reaction requires a specific increase in the chemical reactivity of the reactants. This condition is necessary because it gives the cell the ability to control its own chemistry, making it important. The regulation is carried out with the assistance of specific biological catalysts. Although there are also RNA catalysts known as ribozymes, enzymes are almost always proteins. Ribozymes are an exception to this rule. Each enzyme is only capable of speeding up or catalyzing a single sort of reaction out of the potentially infinite number of transformations that a single molecule could go through. The reactions that are catalyzed by enzymes are linked together in a sequence in such a way that the end product of one reaction serves as the substrate or starting material for the subsequent reaction. When long linear reaction pathways are connected to one another in turn, a maze of interconnected reactions is formed. This maze of reactions is what enables the cell to survive, grow, and reproduce.

The breakdown of food into smaller molecules by catabolic pathways, which produce some of the small molecules the cell needs as building blocks and a useful form of energy for the cell; and the anabolic, or biosynthetic, pathways, which use the small molecules and the energy generated by catabolism to drive the synthesis of the numerous other molecules that make up the cell. These two streams of chemical reactions work in opposition to one another within the cell. These two different kinds of reactions are what make up the cell's metabolism.

Because the vast majority of the particulars of cellular metabolism are typically covered in biochemistry, it is unnecessary to explain them here because they do not pertain to the topic at hand. Cell biology, on the other hand, is predicated on the fundamental notions that enable cells to acquire energy from their environments and use it to the establishment of order within themselves. Let's begin by addressing the question of why it is that all living things require a steady supply of energy.