A microscope is an instrument used to see objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small structures using such an instrument. Microscopic means invisible to the eye. There are many types of microscopes, they may be grouped in different ways. One way is to describe the way the instruments interact with a sample to create images, either by sending a beam of light or electrons to a sample in its optical path, or by scanning across, a short distance from the surface of a sample using a probe; the most common microscope is the optical microscope, which uses light to pass through a sample to produce an image. Other major types of microscopes are the fluorescence microscope, the electron microscope and the various types of scanning probe microscopes. Although objects resembling lenses date back 4000 years and there are Greek accounts of the optical properties of water-filled spheres followed by many centuries of writings on optics, the earliest known use of simple microscopes dates back to the widespread use of lenses in eyeglasses in the 13th century.
The earliest known examples of compound microscopes, which combine an objective lens near the specimen with an eyepiece to view a real image, appeared in Europe around 1620. The inventor is unknown. Several revolve around the spectacle-making centers in the Netherlands including claims it was invented in 1590 by Zacharias Janssen and/or Zacharias' father, Hans Martens, claims it was invented by their neighbor and rival spectacle maker, Hans Lippershey, claims it was invented by expatriate Cornelis Drebbel, noted to have a version in London in 1619. Galileo Galilei seems to have found after 1610 that he could close focus his telescope to view small objects and, after seeing a compound microscope built by Drebbel exhibited in Rome in 1624, built his own improved version. Giovanni Faber coined the name microscope for the compound microscope Galileo submitted to the Accademia dei Lincei in 1625; the first detailed account of the microscopic anatomy of organic tissue based on the use of a microscope did not appear until 1644, in Giambattista Odierna's L'occhio della mosca, or The Fly's Eye.
The microscope was still a novelty until the 1660s and 1670s when naturalists in Italy, the Netherlands and England began using them to study biology. Italian scientist Marcello Malpighi, called the father of histology by some historians of biology, began his analysis of biological structures with the lungs. Robert Hooke's Micrographia had a huge impact because of its impressive illustrations. A significant contribution came from Antonie van Leeuwenhoek who achieved up to 300 times magnification using a simple single lens microscope, he sandwiched a small glass ball lens between the holes in two metal plates riveted together, with an adjustable-by-screws needle attached to mount the specimen. Van Leeuwenhoek re-discovered red blood cells and spermatozoa, helped popularise the use of microscopes to view biological ultrastructure. On 9 October 1676, van Leeuwenhoek reported the discovery of micro-organisms; the performance of a light microscope depends on the quality and correct use of the condensor lens system to focus light on the specimen and the objective lens to capture the light from the specimen and form an image.
Early instruments were limited until this principle was appreciated and developed from the late 19th to early 20th century, until electric lamps were available as light sources. In 1893 August Köhler developed a key principle of sample illumination, Köhler illumination, central to achieving the theoretical limits of resolution for the light microscope; this method of sample illumination produces lighting and overcomes the limited contrast and resolution imposed by early techniques of sample illumination. Further developments in sample illumination came from the discovery of phase contrast by Frits Zernike in 1953, differential interference contrast illumination by Georges Nomarski in 1955. In the early 20th century a significant alternative to the light microscope was developed, an instrument that uses a beam of electrons rather than light to generate an image; the German physicist, Ernst Ruska, working with electrical engineer Max Knoll, developed the first prototype electron microscope in 1931, a transmission electron microscope.
The transmission electron microscope works on similar principles to an optical microscope but uses electrons in the place of light and electromagnets in the place of glass lenses. Use of electrons, instead of light, allows for much higher resolution. Development of the transmission electron microscope was followed in 1935 by the development of the scanning electron microscope by Max Knoll. Although TEMs were being used for research before WWII, became popular afterwards, the SEM was not commercially available until 1965. Transmission electron microscopes became popular following the Second World War. Ernst Ruska, working at Siemens, developed the first commercial transmission electron microscope and, in the 1950s, major scientific conferences on electron microscopy started being held. In 1965, the first commercial scanning electron microscope was developed by Profess
A macromolecule is a large molecule, such as protein created by the polymerization of smaller subunits. They are composed of thousands of atoms or more; the most common macromolecules in biochemistry are large non-polymeric molecules. Synthetic macromolecules include common plastics and synthetic fibers as well as experimental materials such as carbon nanotubes; the term macromolecule was coined by Nobel laureate Hermann Staudinger in the 1920s, although his first relevant publication on this field only mentions high molecular compounds. At that time the phrase polymer, as introduced by Berzelius in 1833, had a different meaning from that of today: it was another form of isomerism for example with benzene and acetylene and had little to do with size. Usage of the term to describe large molecules varies among the disciplines. For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry, the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not dissociate.
According to the standard IUPAC definition, the term macromolecule as used in polymer science refers only to a single molecule. For example, a single polymeric molecule is appropriately described as a "macromolecule" or "polymer molecule" rather than a "polymer," which suggests a substance composed of macromolecules; because of their size, macromolecules are not conveniently described in terms of stoichiometry alone. The structure of simple macromolecules, such as homopolymers, may be described in terms of the individual monomer subunit and total molecular mass. Complicated biomacromolecules, on the other hand, require multi-faceted structural description such as the hierarchy of structures used to describe proteins. In British English, the word "macromolecule" tends to be called "high polymer". Macromolecules have unusual physical properties that do not occur for smaller molecules. Another common macromolecular property that does not characterize smaller molecules is their relative insolubility in water and similar solvents, instead forming colloids.
Many require particular ions to dissolve in water. Many proteins will denature if the solute concentration of their solution is too high or too low. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules, through an effect known as macromolecular crowding; this comes from macromolecules excluding other molecules from a large part of the volume of the solution, thereby increasing the effective concentrations of these molecules. All living organisms are dependent on three essential biopolymers for their biological functions: DNA, RNA and proteins; each of these molecules is required for life since each plays a distinct, indispensable role in the cell. The simple summary is that DNA makes RNA, RNA makes proteins. DNA, RNA, proteins all consist of a repeating structure of related building blocks. In general, they are all unbranched polymers, so can be represented in the form of a string. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into a long chain.
In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. In DNA and RNA, this can take the form of Watson-Crick base pairs, although many more complicated interactions can and do occur; because of the double-stranded nature of DNA all of the nucleotides take the form of Watson-Crick base pairs between nucleotides on the two complementary strands of the double-helix. In contrast, both RNA and proteins are single-stranded. Therefore, they are not constrained by the regular geometry of the DNA double helix, so fold into complex three-dimensional shapes dependent on their sequence; these different shapes are responsible for many of the common properties of RNA and proteins, including the formation of specific binding pockets, the ability to catalyse biochemical reactions. DNA is an information storage macromolecule that encodes the complete set of instructions that are required to assemble and reproduce every living organism. DNA and RNA are both capable of encoding genetic information, because there are biochemical mechanisms which read the information coded within a DNA or RNA sequence and use it to generate a specified protein.
On the other hand, the sequence information of a protein molecule is not used by cells to functionally encode genetic information. DNA has three primary attributes that allow it to be far better than RNA at encoding genetic information. First, it is double-stranded, so that there are a minimum of two copies of the information encoding each gene in every cell. Second, DNA has a much greater stability against breakdown than does RNA, an attribute associated with the absence of the 2'-hydroxyl group within every nucleotide of DNA. Third sophisticated DNA surveillance and repair systems are present which monitor damage to the DNA and repair the sequence when necessary. Analogous systems have not evolved for repairing damaged RNA molecules. Chromosomes can contain many billions of atoms, arranged in a specific chemical structure. Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life. Proteins carry out all functions of an organism, for example p
A molecular model, in this article, is a physical model that represents molecules and their processes. The creation of mathematical models of molecular properties and behaviour is molecular modelling, their graphical depiction is molecular graphics, but these topics are linked and each uses techniques from the others. In this article, "molecular model" will refer to systems containing more than one atom and where nuclear structure is neglected; the electronic structure is also omitted or represented in a sophisticated way. Physical models of atomistic systems have played an important role in understanding chemistry and generating and testing hypotheses. Most there is an explicit representation of atoms, though other approaches such as soap films and other continuous media have been useful. There are several motivations for creating physical models: as pedagogic tools for students or those unfamiliar with atomistic structures; the construction of physical models is a creative act, many bespoke examples have been created in the workshops of science departments.
There is a wide range of approaches to physical modelling, this article lists only the most common or important. The main strategies are: bespoke construction of a single model. Models encompass a wide range of degrees of precision and engineering: some models such as J. D. Bernal's water are conceptual, while the macromodels of Pauling and Crick and Watson were created with much greater precision. Molecular models have inspired molecular graphics in textbooks and research articles and more on computers. Molecular graphics has replaced some functions of physical molecular models, but physical kits continue to be popular and are sold in large numbers, their unique strengths include: cheapness and portability. In the 1600s, Johannes Kepler speculated on the symmetry of snowflakes and on the close packing of spherical objects such as fruit; the symmetrical arrangement of packed spheres informed theories of molecular structure in the late 1800s, many theories of crystallography and solid state inorganic structure used collections of equal and unequal spheres to simulate packing and predict structure.
John Dalton represented compounds as aggregations of circular atoms, although Johann Josef Loschmidt did not create physical models, his diagrams based on circles are two-dimensional analogues of models. August Wilhelm von Hofmann is credited with the first physical molecular model around 1860. Note how the size of the carbon appears smaller than the hydrogen; the importance of stereochemistry was not recognised and the model is topological. Jacobus Henricus van't Hoff and Joseph Le Bel introduced the concept of chemistry in space—stereochemistry in three dimensions. Van't Hoff built tetrahedral molecules representing the three-dimensional properties of carbon. Repeating units will help to show how easy it is and clear it is to represent molecules through balls that represent atoms; the binary compounds sodium chloride and caesium chloride have cubic structures but have different space groups. This can be rationalised in terms of close packing of spheres of different sizes. For example, NaCl can be described as close-packed chloride ions with sodium ions in the octahedral holes.
After the development of X-ray crystallography as a tool for determining crystal structures, many laboratories built models based on spheres. With the development of plastic or polystyrene balls it is now easy to create such models; the concept of the chemical bond as a direct link between atoms can be modelled by linking balls with sticks/rods. This has been popular and is still used today. Atoms were made of spherical wooden balls with specially drilled holes for rods, thus carbon can be represented as a sphere with four holes at the tetrahedral angles cos−1 ≈ 109.47°. A problem with rigid bonds and holes is; this can be overcome with flexible bonds helical springs but now plastic. This allows double and triple bonds to be approximated by multiple single bonds. Figure 3 represents a ball-and-stick model of proline; the balls have colours: black represents carbon. Each ball is drilled with as many holes as its conventional valence directed towards the vertices of a tetrahedron. Single bonds are represented by rigid grey rods.
Double and triple bonds use two longer flexible bonds which restrict rotation and support conventional cis/trans stereochemistry. However, most molecules require holes at other angles and specialist companies manufacture kits and bespoke models. Besides tetrahedral and octahedral holes, there were all-purpose balls with 24 holes; these models allowed rotation about the single rod bonds, which could be both an advantage and a disadvantage. The approximate scale was 5 cm per ångström, but was not consistent over
Cell biology is a branch of biology that studies the structure and function of the cell, the basic unit of life. Cell biology is concerned with the physiological properties, metabolic processes, signaling pathways, life cycle, chemical composition and interactions of the cell with their environment; this is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells. Knowing the components of cells and how cells work is fundamental to all biological sciences. Research in cell biology is related to genetics, molecular biology and cytochemistry. Cells, which were once invisible to the naked eye, were first seen in 17th century Europe with the invention of the compound microscope. Robert Hooke was the first person to term the building block of all living organisms as "cells" after looking at cork; the cell theory states. The theory states that both plants and animals are composed of cells, confirmed by plant scientist, Matthias Schleiden and animal scientist, Theodor Schwann in 1839.
19 years Rudolf Virchow contributed to the cell theory, arguing that all cells come from the division of preexisting cells. In recent years, there have been many studies. Scientists have struggled to decide. Viruses lack common characteristics of a living cell, such as membranes, cell organelles, the ability to reproduce by themselves. Viruses range from 0.005 to 0.03 micrometers in size. Modern day cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology, to derive treatments and other medications, etc; the techniques by which cells are studied have evolved. Advancement in microscopic techniques and technology such as fluorescence microscopy, phase-contrast microscopy, dark field microscopy, confocal microscopy, transmission electron microscopy, etc. have allowed scientists to get a better idea of the structure of cells. There are two fundamental classifications of cells: eukaryotes; the major difference between the two is the absence of organelles.
Other factors such as size, the way in which they reproduce, the number of cells distinguish them from one another. Eukaryotic cells include animal, plant and protozoa cells which all have a nucleus enclosed by a membrane, with various shapes and sizes. Prokaryotic cells, lacking an enclosed nucleus, include bacteria and archaea. Prokaryotic cells are much smaller than eukaryotic cells, making prokaryotic cells the smallest form of life. Cytologists focus on eukaryotic cells whereas prokaryotic cells are the focus of microbiologists, but this is not always the case; the study of the cell is done on a molecular level. 75-85% of the cell's volume is due to water making it an indispensable solvent as a result of its polarity and structure. These molecules within the cell, which operate as substrates, provide a suitable environment for the cell to carry out metabolic reactions and signalling; the cell shape varies among the different types of organisms, are thus classified into two categories: eukaryotes and prokaryotes.
In the case of eukaryotic cells - which are made up of animal, plant and protozoa cells - the shapes are round and spherical or oval while for prokaryotic cells – which are composed of bacteria and archaea - the shapes are: spherical, rods and spirals. Cell biology focuses more on the study of eukaryotic cells, their signalling pathways, rather than on prokaryotes, covered under microbiology; the main constituents of the general molecular composition of the cell includes: proteins and lipids which are either free flowing or membrane bound, along with different internal compartments known as organelles. This environment of the cell is made up of hydrophilic and hydrophobic regions which allows for the exchange of the above-mentioned molecules and ions; the hydrophilic regions of the cell are on the inside and outside of the cell, while the hydrophobic regions are within the phospholipid bilayer of the cell membrane. The cell membrane consists of lipids and proteins which accounts for its hydrophobicity as a result of being non-polar substances.
Therefore, in order for these molecules to participate in reactions, within the cell, they need to be able to cross this membrane layer to get into the cell. They accomplish this process of gaining access to the cell via: osmotic pressure, concentration gradients, membrane channels. Inside of the cell are extensive internal sub-cellular membrane-bounded compartments called organelles. Cells contain specialized sub-cellular compartments including cell membrane, cytoplasm,mitochondria, ribosomes. See organelle; the growth process of the cell does not refer to the size of the cell, but instead the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops. Cells are the foundation of all organisms, they are the fundamental unit of life; the growth and development of the cell are essential for the maintenance of the host, survival of the organisms. For this process the cell goes through the steps of
Molecular biology is a branch of biology that concerns the molecular basis of biological activity between biomolecules in the various systems of a cell, including the interactions between DNA, RNA, proteins and their biosynthesis, as well as the regulation of these interactions. Writing in Nature in 1961, William Astbury described molecular biology as:...not so much a technique as an approach, an approach from the viewpoint of the so-called basic sciences with the leading idea of searching below the large-scale manifestations of classical biology for the corresponding molecular plan. It is concerned with the forms of biological molecules and is predominantly three-dimensional and structural – which does not mean, that it is a refinement of morphology, it must at the same time inquire into function. Researchers in molecular biology use specific techniques native to molecular biology but combine these with techniques and ideas from genetics and biochemistry. There is not a defined line between these disciplines.
This is shown in the following schematic that depicts one possible view of the relationships between the fields: Biochemistry is the study of the chemical substances and vital processes occurring in live organisms. Biochemists focus on the role and structure of biomolecules; the study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry. Genetics is the study of the effect of genetic differences in organisms; this can be inferred by the absence of a normal component. The study of "mutants" – organisms which lack one or more functional components with respect to the so-called "wild type" or normal phenotype. Genetic interactions can confound simple interpretations of such "knockout" studies. Molecular biology is the study of molecular underpinnings of the processes of replication, transcription and cell function; the central dogma of molecular biology where genetic material is transcribed into RNA and translated into protein, despite being oversimplified, still provides a good starting point for understanding the field.
The picture has been revised in light of emerging novel roles for RNA. Much of molecular biology is quantitative, much work has been done at its interface with computer science in bioinformatics and computational biology. In the early 2000s, the study of gene structure and function, molecular genetics, has been among the most prominent sub-fields of molecular biology. Many other areas of biology focus on molecules, either directly studying interactions in their own right such as in cell biology and developmental biology, or indirectly, where molecular techniques are used to infer historical attributes of populations or species, as in fields in evolutionary biology such as population genetics and phylogenetics. There is a long tradition of studying biomolecules "from the ground up" in biophysics. One of the most basic techniques of molecular biology to study protein function is molecular cloning. In this technique, DNA coding for a protein of interest is cloned using polymerase chain reaction, and/or restriction enzymes into a plasmid.
A vector has 3 distinctive features: an origin of replication, a multiple cloning site, a selective marker antibiotic resistance. Located upstream of the multiple cloning site are the promoter regions and the transcription start site which regulate the expression of cloned gene; this plasmid can be inserted into either bacterial or animal cells. Introducing DNA into bacterial cells can be done by transformation via uptake of naked DNA, conjugation via cell-cell contact or by transduction via viral vector. Introducing DNA into eukaryotic cells, such as animal cells, by physical or chemical means is called transfection. Several different transfection techniques are available, such as calcium phosphate transfection, electroporation and liposome transfection; the plasmid may be integrated into the genome, resulting in a stable transfection, or may remain independent of the genome, called transient transfection. DNA coding for a protein of interest is now inside a cell, the protein can now be expressed.
A variety of systems, such as inducible promoters and specific cell-signaling factors, are available to help express the protein of interest at high levels. Large quantities of a protein can be extracted from the bacterial or eukaryotic cell; the protein can be tested for enzymatic activity under a variety of situations, the protein may be crystallized so its tertiary structure can be studied, or, in the pharmaceutical industry, the activity of new drugs against the protein can be studied. Polymerase chain reaction is an versatile technique for copying DNA. In brief, PCR allows a specific DNA sequence to be modified in predetermined ways; the reaction is powerful and under perfect conditions could amplify one DNA molecule to become 1.07 billion molecules in less than two hours. The PCR technique can be used to introduce restriction enzyme sites to ends of DNA molecules, or to mutate particular bases of DNA, the latter is a method referred to as site-directed mutagenesis. PCR can be used to determine whether a particular DNA fragment is found in a cDNA library.
PCR has many variations, like reverse transcription PCR for amplification of RNA, more quantitative PCR which allow for quantitative measurement of DNA or RNA molecules. Gel electrophoresis is one of the principal tools of molecular biology; the basic principle is that DNA, RNA, proteins can all be separated by means of an electric field and size. In agarose gel electrophoresis, DNA and RNA can be separated on th
Glossary of chemistry terms
This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws and formulae, laboratory tools and equipment. Chemistry is a physical science concerned with the composition and properties of matter, as well as the changes it undergoes during chemical reactions. Note: All periodic table references refer to the IUPAC Style of the Periodic Table. Absolute zero A theoretical condition concerning a system at the lowest limit of the thermodynamic temperature scale, or zero kelvins, where a system does not emit or absorb energy. By extrapolating the ideal gas law, the internationally accepted value for absolute zero has been determined as −273.15 °C. absorbance abundance accuracy How close a measured value is to the actual or true value. Compare precision. Acid A compound which, when dissolved in water, gives a pH of less than 7.0, or donates a hydrogen ion. acid anhydride A compound with two acyl groups bound to a single oxygen atom. Acid dissociation constant Also called acid ionization acidity constant.
A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is denoted by the symbol Ka. actinides Also called the actinoids. The periodic series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium. Activated complex A structure that forms because of a collision between molecules while new bonds are formed. Activation energy The minimum energy which must be available to a chemical system with potential reactants in order to result in a chemical reaction. Activity series actual yield acyclic Containing only linear structures of atoms. Addition reaction In organic chemistry, when two or more molecules combine to make a larger one. Adhesion The tendency of dissimilar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast cohesion. Aeration The mixing of air into a liquid or a solid. Alcohol Any organic compound consisting of a hydroxyl functional group attached to a saturated carbon atom.
Aldehyde Any organic compound consisting of a carbonyl group attached to a hydrogen atom and any other R-group. Alkali metal Any of the metallic elements belonging to Group 1 of the periodic table: lithium, potassium, rubidium and francium. Alkaline earth metal Any of the metallic elements belonging to Group 2 of the periodic table: beryllium, calcium, strontium and radium. Alkane Any saturated acyclic hydrocarbon. Alkene An unsaturated hydrocarbon containing at least one pair of double-bonded carbons. Alkyl group A functional group consisting of an alkane missing a hydrogen atom. Alkyne An unsaturated hydrocarbon containing at least one pair of triple-bonded carbons. Allomer A substance that differs in chemical composition but has the same crystalline structure as another substance. Allotrope Elements. Alloy A mixture of metals or of a metal and another element which in combination exhibit a metallic bonding character. Common examples include bronze and pewter. Amalgam amplitude The maximum distance that the particles of the medium carrying the wave move away from their rest position.
Analyte analytical chemistry anion A negatively charged ion. anode 1. An electrode through which the conventional electric current enters into a polarized electrical circuit. 2. The wire or plate of an electrochemical cell having an excess positive charge. Negatively charged anions always move toward the anode. Contrast cathode. Aqueous solution A solution, it is denoted in chemical equations by appending to a chemical formula. Aromaticity A chemical property of conjugated rings of atoms, such as benzene, which results in unusually high stability. Atom A chemical element in its smallest form, made up of protons and neutrons within the nucleus and electrons circling the nucleus. Atomic mass The mass of an atom expressed in unified atomic mass units and nearly equivalent to the mass number. Atomic mass unit See unified atomic mass unit. Atomic number Also called proton number; the number of protons found in the nucleus of an atom of a given chemical element. It is identical to the charge number of the nucleus and is used in the periodic table to uniquely identify each chemical element.
Atomic orbital the region where the electron of the atom may be found atomic radius atomic weight average atomic mass Avogadro's law Avogadro's number The number of particles in one mole of a substance, defined as 6.022×1023 particles. Azeotrope A mixture of liquids whose composition is unchanged by distillation. Barometer A device used to measure atmospheric pressure. Base A substance that accepts a proton and has a pH above 7.0. A common example is sodium hydroxide. Base anhydride Oxides of group I and II metal elements. Beaker Beer–Lambert law biochemistry The study of the chemistry of biological systems and organisms. Bohr model boiling See vaporization. Boiling point The temperature. Boiling-point elevation the process where the boiling point is elevated by adding a substance bond The attraction and repulsion between atoms and molecules, a cornerstone of chemistry. Boyle's law for a given mass of gas at constant temperature, the volume varies inversely with the pressure Bragg's law Brønsted–Lowry acid Any chemical species that dona
History of biochemistry
The history of biochemistry can be said to have started with the ancient Greeks who were interested in the composition and processes of life, although biochemistry as a specific scientific discipline has its beginning around the early 19th century. Some argued that the beginning of biochemistry may have been the discovery of the first enzyme, diastase, in 1833 by Anselme Payen, while others considered Eduard Buchner's first demonstration of a complex biochemical process alcoholic fermentation in cell-free extracts to be the birth of biochemistry; some might point to the influential work of Justus von Liebig from 1842, Animal chemistry, or, Organic chemistry in its applications to physiology and pathology, which presented a chemical theory of metabolism, or earlier to the 18th century studies on fermentation and respiration by Antoine Lavoisier. The term “biochemistry” itself is derived from the combining form bio-, meaning "life", chemistry; the word is first recorded in English in 1848, while in 1877, Felix Hoppe-Seyler used the term in the foreword to the first issue of Zeitschrift für Physiologische Chemie as a synonym for physiological chemistry and argued for the setting up of institutes dedicate to its studies.
Several sources cite German chemist Carl Neuberg as having coined the term for the new discipline in 1903, some credit it to Franz Hofmeister. The subject of study in biochemistry is the chemical processes in living organisms, its history involves the discovery and understanding of the complex components of life and the elucidation of pathways of biochemical processes. Much of biochemistry deals with the structures and functions of cellular components such as proteins, lipids, nucleic acids and other biomolecules. Over the last 40 years the field has had success in explaining living processes such that now all areas of the life sciences from botany to medicine are engaged in biochemical research. Among the vast number of different biomolecules, many are complex and large molecules, which are composed of similar repeating subunits; each class of polymeric biomolecule has a different set of subunit types. For example, a protein is a polymer whose subunits are selected from a set of twenty or more amino acids, carbohydrates are formed from sugars known as monosaccharides and polysaccharides, lipids are formed from fatty acids and glycerols, nucleic acids are formed from nucleotides.
Biochemistry studies the chemical properties of important biological molecules, like proteins, in particular the chemistry of enzyme-catalyzed reactions. The biochemistry of cell metabolism and the endocrine system has been extensively described. Other areas of biochemistry include the genetic code, protein synthesis, cell membrane transport, signal transduction. In a sense, the study of biochemistry can be considered to have started in ancient times, for example when biology first began to interest society—as the ancient Chinese developed a system of medicine based on yin and yang, the five phases, which both resulted from alchemical and biological interests, its beginning in the ancient Indian culture was linked to an interest in medicine, as they developed the concept of three humors that were similar to the Greek's four humours. They delved into the interest of bodies being composed of tissues; the ancient Greeks conception of "biochemistry" was linked with their ideas on matter and disease, where good health was thought to come from a balance of the four elements and four humors in the human body.
As in the majority of early sciences, the Islamic world contributed to early biological advancements as well as alchemical advancements. On the side of chemistry, early advancements were attributed to exploration of alchemical interests but included: metallurgy, the scientific method, early theories of atomism. In more recent times, the study of chemistry was marked by milestones such as the development of Mendeleev's periodic table, Dalton's atomic model, the conservation of mass theory; this last mention has the most importance of the three due to the fact that this law intertwines chemistry with thermodynamics in an intercalated manner. As early as the late 18th century and early 19th century, the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were known. However, the mechanism by which this occurred had not been identified. In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was catalyzed by a vital force contained within the yeast cells called ferments, which he thought functioned only within living organisms.
He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."Anselme Payen discovered in 1833 the first enzyme who called diastase and in 1878 German physiologist Wilhelm Kühne coined the term enzyme, which comes from Greek ενζυμον "in leaven", to describe this process. The word enzyme was used to refer to nonliving substances such as pepsin, the word ferment used to refer to chemical activity produced by l