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Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA.
In 1665, Robert Hooke referred to the building blocks of all living organisms as "cells" (published in Micrographia) after looking at a piece of cork and observing a structure reminiscent of a monastic cell; [4] [5] however, the cells were dead. They gave no indication to the actual overall components of a cell.
Peptide, building block of proteins. [2] Lipids, which also store energy, but in a more concentrated form, and which may be stored for extended periods in the bodies of animals. [2] Phospholipid used in cell membrane. [2] Carbohydrates, which store energy in a form that can be used by living cells. [2] Lectin, for binding proteins. [28]
Lipids (oleaginous) are chiefly fatty acid esters, and are the basic building blocks of biological membranes. Another biological role is energy storage (e.g., triglycerides). Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three non polar or hydrophobic fatty acid tails, and therefore they are amphiphilic.
A large fraction of the chemical elements that occur naturally on the Earth's surface are essential to the structure and metabolism of living things. Four of these elements (hydrogen, carbon, nitrogen, and oxygen) are essential to every living thing and collectively make up 99% of the mass of protoplasm. [1]
The emergence of life with increasing order and complexity does not contradict the second law of thermodynamics, which states that overall entropy never decreases, since a living organism creates order in some places (e.g. its living body) at the expense of an increase of entropy elsewhere (e.g. heat and waste production). [164] [165] [166]
All living things contain two types of large molecule, proteins and nucleic acids, the latter usually both DNA and RNA: these carry the information needed by each species, including the instructions to make each type of protein. The proteins, in turn, serve as the machinery which carries out the many chemical processes of life.
The single-stranded nature of protein molecules, together with their composition of 20 or more different amino acid building blocks, allows them to fold in to a vast number of different three-dimensional shapes, while providing binding pockets through which they can specifically interact with all manner of molecules.