Biochemistry

History

Main article: History of biochemistry

  Originally, it was generally believed that life was not subject to the laws of science the way non-life was. It was thought that only living beings could produce the molecules of life (from other, previously existing biomolecules). Then, in 1828, organic compounds can be created artificially.^[2][3]

The dawn of biochemistry may have been the discovery of the first enzyme, Krebs cycle (citric acid cycle).

Today, there are three main types of biochemistry as established by Michael E. Sugar. Plant biochemistry involves the study of the biochemistry of autotrophic organisms such as biochemical processes. General biochemistry encompasses both plant and animal biochemistry . Human/medical/medicinal biochemistry focuses on the biochemistry of humans and medical illnesses.

Carbohydrates

Main article: Carbohydrate

The function of carbohydrates includes energy storage and providing structure. Sugars are carbohydrates, but not all carbohydrates are sugars. There are more carbohydrates on Earth than any other known type of biomolecule.

Monosaccharides

  The simplest type of carbohydrate is a heterocyclic rings containing one O as heteroatom.

Disaccharides

  Two monosaccharides can be joined together using lactase, the enzyme that hydrolyzes lactose back into glucose and galactose, typically decreases. This results in lactase deficiency, also called lactose intolerance.

Sugar polymers are characterised by having reducing or non-reducing ends. A reducing end of a carbohydrate is a carbon atom which can be in equilibrium with the open-chain acetal. This prevents opening of the chain to the aldehyde or keto form and renders the modified residue non-reducing. Lactose contains a reducing end at its glucose moiety, whereas the galactose moiety form a full acetal with the C4-OH group of glucose. Saccharose does not have a reducing end because of full acetal formation between the aldehyde carbon of glucose (C1) and the keto carbon of fructose (C2).

Oligosaccharides and polysaccharides

  When a few (around three to six) monosaccharides are joined together, it is called an oligosaccharide (oligo- meaning "few"). These molecules tend to be used as markers and signals, as well as having some other uses.

Many monosaccharides joined together make a monomers.

• Cellulose is made by plants and is an important structural component of their cell walls. Humans can neither manufacture nor digest it.
• Glycogen, on the other hand, is an animal carbohydrate; humans and other animals use it as a form of energy storage.

Use of carbohydrates as an energy source

See also carbohydrate metabolism

Glucose is the major energy source in most life forms. For instance, polysaccharides are broken down into their monomers (sucrose are cleaved into their two component monosaccharides.

Glycolysis (anaerobic)

Glucose is mainly metabolized by a very important and ancient ten-step pathway called yeast). Other monosaccharides like galactose and fructose can be converted into intermediates of the glycolytic pathway.

Aerobic

In oxygen and conserving the released energy in the form of a proton gradient over a membrane (inner mitochondrial membrane in eukaryotes). Thereby, oxygen is reduced to water and the original electron acceptors NAD⁺ and quinone are regenerated. This is why humans breathe in oxygen and breathe out carbon dioxide. The energy released from transferring the electrons from high-energy states in NADH and quinol is conserved first as proton gradient and converted to ATP via ATP synthase. This generates an additional 28 molecules of ATP (24 from the 8 NADH + 4 from the 2 quinols), totaling to 32 molecules of ATP conserved per degraded glucose (two from glycolysis + two from the citrate cycle). It is clear that using oxygen to completely oxidize glucose provides an organism with far more energy than any oxygen-independent metabolic feature, and this is thought to be the reason why complex life appeared only after Earth's atmosphere accumulated large amounts of oxygen.

Gluconeogenesis

Main article: Gluconeogenesis

In vertebrates, vigorously contracting skeletal muscles (during weightlifting or sprinting, for example) do not receive enough oxygen to meet the energy demand, and so they shift to gluconeogenesis. This process is not quite the opposite of glycolysis, and actually requires three times the amount of energy gained from glycolysis (six molecules of ATP are used, compared to the two gained in glycolysis). Analogous to the above reactions, the glucose produced can then undergo glycolysis in tissues that need energy, be stored as glycogen (or starch in plants), or be converted to other monosaccharides or joined into di- or oligosaccharides.

Proteins

Main article: Protein

  Like carbohydrates, some proteins perform largely structural roles. For instance, movements of the proteins activation energy, the enzyme speeds up that reaction by a rate of 10¹¹ or more: a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates. Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.

In essence, proteins are chains of neurotransmitter.

  Amino acids can be joined together via a albumin contains 585 amino acid residues.

The structure of proteins is traditionally described in a hierarchy of four levels. The quaternary structure is concerned with the structure of a protein with multiple peptide subunits, like hemoglobin with its four subunits. Not all proteins have more than one subunit.

Ingested proteins are usually broken up into single amino acids or dipeptides in the small intestine, and then absorbed. They can then be joined together to make new proteins. Intermediate products of glycolysis, the citric acid cycle, and the histidine, they cannot produce it in sufficient amounts for young, growing animals, and so these are often considered essential amino acids.

If the amino group is removed from an amino acid, it leaves behind a carbon skeleton called an α-keto acid. Enzymes called transamination. The amino acids may then be linked together to make a protein.

A similar process is used to break down proteins. It is first hydrolyzed into its component amino acids. Free urea cycle.

Lipids

Main article: Lipid

The term lipid comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or aromatic, while others are not. Some are flexible, while others are rigid.

Most lipids have some cholesterol, the polar group is a mere -OH (hydroxyl or alcohol). In the case of phospholipids, the polar groups are considerably larger and more polar, as described below.

Lipids are an integral part of our daily diet. Most oils and milk products that we use for cooking and eating like butter, cheese, ghee etc, are comprised of fats. glycerol, which are the final degradation products of fats and lipids.

Nucleic acids

Main article: Nucleic acid

A nucleic acid is a complex, high-molecular-weight biochemical RNA). Nucleic acids are found in all living cells and viruses.

Nucleic acid, so called because of its prevalence in cellular nuclei, is the generic name of the family of uracil occurs in RNA.

Relationship to other "molecular-scale" biological sciences

  Researchers in biochemistry use specific techniques native to biochemistry, but increasingly combine these with techniques and ideas from genetics, molecular biology and biophysics. There has never been a hard-line between these disciplines in terms of content and technique, but members of each discipline have in the past been very territorial; today the terms molecular biology and biochemistry are nearly interchangeable. The following figure is a schematic that depicts one possible view of the relationship between the fields:

• Biochemistry is the study of the chemical substances and vital processes occurring in living organisms. 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 on organisms. Often this can be inferred by the absence of a normal component (e.g. one gene). 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 (epistasis) can often confound simple interpretations of such "knock-out" studies.
• Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field. This picture, however, is undergoing revision in light of emerging novel roles for RNA.
• Chemical Biology seeks to develop new tools based on small molecules that allow minimal perturbation of biological systems while providing detailed information about their function. Further, chemical biology employs biological systems to create non-natural hybrids between biomolecules and synthetic devices (for example emptied viral capsids that can deliver gene therapy or drug molecules).

References

This article is missing citations or needs footnotes. Using inline citations helps guard against copyright violations and factual inaccuracies. (July 2007)

Further reading

• Hunter, Graeme K. (2000). Vital Forces: The Discovery of the Molecular Basis of Life. San Diego: Academic Press. ISBN 0-12-361810-X. 
• Proceedings of National academy of Science of the United States of America, ISSN: 1091-6490 (electronic)

See also

Lists

Related topics

• The Virtual Library of Biochemistry and Cell Biology
• Biochemistry, 5th ed. Full text of Berg, Tymoczko, and Stryer, courtesy of NCBI.
• Biochemistry, 2nd ed. Full text of Garrett and Grisham.

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