By controlling information flow through biochemical signalling and the flow of chemical energy through metabolism, biochemical processes give rise to the complexity of life. Over the last 40 years, biochemistry has become useful at explaining living processes that now almost all areas of the life sciences from botany to medicine are engaged in biochemical research.
The citric acid cycle is typical biochemistry topic because it details with basic chemistry within all living system for metabolism. Today, the main focus of pure biochemistry is in understanding how biological molecules give rise to the processes that occur within living cells, which in turn relates greatly to the study and understanding of whole organisms. Biochemistry is closely related to molecular biology , the study of the molecular mechanisms by which genetic information encoded in DNA is able to result in the processes of life.
Depending on the exact definition of the terms used, molecular biology can be thought of as a branch of biochemistry, or biochemistry as a tool with which to investigate and study molecular biology. Much of biochemistry deals with the structures, functions and interactions of biological macromolecules, such as proteins , nucleic acids, carbohydrates and lipids, which provide the structure of cells and perform many of the functions associated with life. The chemistry of the cell also depends on the reactions of smaller molecules and ions.
These can be inorganic, for example water and metal ions, or organic, for example the amino acids which are used to synthesize proteins. The mechanisms by which cells harness energy from their environment via chemical reactions are known as metabolism. The findings of biochemistry are applied primarily in medicine , nutrition, and agriculture. In medicine, biochemists investigate the causes and cures of disease. In these cyclic forms, the ring usually has 5 or 6 atoms.
These forms are called furanoses and pyranoses , respectively—by analogy with furan and pyran , the simplest compounds with the same carbon-oxygen ring although they lack the carbon-carbon double bonds of these two molecules. For example, the aldohexose glucose may form a hemiacetal linkage between the hydroxyl on carbon 1 and the oxygen on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose.
The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called glucopyranose. Cyclic forms with a 7-atom ring called heptoses are rare. Two monosaccharides can be joined together by a glycosidic or ether bond into a disaccharide through a dehydration reaction during which a molecule of water is released. The reverse reaction in which the glycosidic bond of a disaccharide is broken into two monosaccharides is termed hydrolysis.
The best-known disaccharide is sucrose or ordinary sugar , which consists of a glucose molecule and a fructose molecule joined together. Another important disaccharide is lactose found in milk, consisting of a glucose molecule and a galactose molecule. Lactose may be hydrolysed by lactase , and deficiency in this enzyme results in lactose intolerance. When a few around three to six monosaccharides are joined, 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. They can be joined together in one long linear chain, or they may be branched. Two of the most common polysaccharides are cellulose and glycogen , both consisting of repeating glucose monomers. Cellulose is an important structural component of plant's cell walls and glycogen is used as a form of energy storage in animals.
Sugar can be characterized by having reducing or non-reducing ends. A reducing end of a carbohydrate is a carbon atom that can be in equilibrium with the open-chain aldehyde aldose or keto form ketose. If the joining of monomers takes place at such a carbon atom, the free hydroxy group of the pyranose or furanose form is exchanged with an OH-side-chain of another sugar, yielding a full 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 forms 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. Lipids comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including waxes , fatty acids , fatty-acid derived phospholipids , sphingolipids , glycolipids , and terpenoids e. Some lipids are linear, open chain aliphatic molecules, while others have ring structures. Some are aromatic with a cyclic [ring] and planar [flat] structure while others are not.
Some are flexible, while others are rigid. Lipids are usually made from one molecule of glycerol combined with other molecules. In triglycerides , the main group of bulk lipids, there is one molecule of glycerol and three fatty acids. Fatty acids are considered the monomer in that case, and may be saturated no double bonds in the carbon chain or unsaturated one or more double bonds in the carbon chain.
Most lipids have some polar character in addition to being largely nonpolar. In general, the bulk of their structure is nonpolar or hydrophobic "water-fearing" , meaning that it does not interact well with polar solvents like water. Another part of their structure is polar or hydrophilic "water-loving" and will tend to associate with polar solvents like water.
This makes them amphiphilic molecules having both hydrophobic and hydrophilic portions. In the case of 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. Vegetable oils are rich in various polyunsaturated fatty acids PUFA.
Lipid-containing foods undergo digestion within the body and are broken into fatty acids and glycerol, which are the final degradation products of fats and lipids. Lipids, especially phospholipids , are also used in various pharmaceutical products , either as co-solubilisers e.
Proteins are very large molecules—macro-biopolymers—made from monomers called amino acids. The side chain "R" is different for each amino acid of which there are 20 standard ones. It is this "R" group that made each amino acid different, and the properties of the side-chains greatly influence the overall three-dimensional conformation of a protein. Some amino acids have functions by themselves or in a modified form; for instance, glutamate functions as an important neurotransmitter. Amino acids can be joined via a peptide bond.
In this dehydration synthesis, a water molecule is removed and the peptide bond connects the nitrogen of one amino acid's amino group to the carbon of the other's carboxylic acid group. The resulting molecule is called a dipeptide , and short stretches of amino acids usually, fewer than thirty are called peptides or polypeptides.
Longer stretches merit the title proteins.
The demonstration, through the combined work of Joseph Priestley , Jan Ingenhousz , and Jean Senebier , that photosynthesis is essentially the reverse of respiration was a milestone in the development of biochemical thought. Most important is that a Biochemist can choose many careers. Most rare elements on Earth are not needed by life exceptions being selenium and iodine , while a few common ones aluminum and titanium are not used. The molecular biologist will look at the membrane and investigate what is going on there and link it back to what the biochemist has observed. Lastly, genetics concerns with genes and their effects on all living organisms. It deals with the chemistry of life, and as such it draws on the techniques of analytical , organic, and physical chemistry , as well as those of physiologists concerned with the molecular basis of vital processes.
As an example, the important blood serum protein albumin contains amino acid residues. For instance, movements of the proteins actin and myosin ultimately are responsible for the contraction of skeletal muscle. One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be extremely selective in what they bind.
Antibodies are an example of proteins that attach to one specific type of molecule. Antibodies are composed of heavy and light chains. Two heavy chains would be linked to two light chains through disulfide linkages between their amino acids. Antibodies are specific through variation based on differences in the N-terminal domain. In fact, the enzyme-linked immunosorbent assay ELISA , which uses antibodies, is one of the most sensitive tests modern medicine uses to detect various biomolecules.
Probably the most important proteins, however, are the enzymes. Virtually every reaction in a living cell requires an enzyme to lower the activation energy of the reaction.
These molecules recognize specific reactant molecules called substrates ; they then catalyze the reaction between them. By lowering the activation energy , the enzyme speeds up that reaction by a rate of 10 11 or more; a reaction that would normally take over 3, 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. The structure of proteins is traditionally described in a hierarchy of four levels. The primary structure of a protein consists of its linear sequence of amino acids; for instance, "alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-lysine-…". Secondary structure is concerned with local morphology morphology being the study of structure. Tertiary structure is the entire three-dimensional shape of the protein.
This shape is determined by the sequence of amino acids. In fact, a single change can change the entire structure. The alpha chain of hemoglobin contains amino acid residues; substitution of the glutamate residue at position 6 with a valine residue changes the behavior of hemoglobin so much that it results in sickle-cell disease.
Finally, 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 to make new proteins.
Intermediate products of glycolysis, the citric acid cycle, and the pentose phosphate pathway can be used to make all twenty amino acids, and most bacteria and plants possess all the necessary enzymes to synthesize them. Humans and other mammals, however, can synthesize only half of them. They cannot synthesize isoleucine , leucine , lysine , methionine , phenylalanine , threonine , tryptophan , and valine.
These are the essential amino acids , since it is essential to ingest them. Mammals do possess the enzymes to synthesize alanine , asparagine , aspartate , cysteine , glutamate , glutamine , glycine , proline , serine , and tyrosine , the nonessential amino acids. While they can synthesize arginine and histidine , they cannot produce it in sufficient amounts for young, growing animals, and so these are often considered essential amino acids. 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. A suitable method for excreting it must therefore exist. Different tactics have evolved in different animals, depending on the animals' needs. Unicellular organisms simply release the ammonia into the environment. Likewise, bony fish can release the ammonia into the water where it is quickly diluted.
In general, mammals convert the ammonia into urea, via the urea cycle. In order to determine whether two proteins are related, or in other words to decide whether they are homologous or not, scientists use sequence-comparison methods. Methods like sequence alignments and structural alignments are powerful tools that help scientists identify homologies between related molecules.
By finding how similar two protein sequences are, we acquire knowledge about their structure and therefore their function. Nucleic acids , so called because of their prevalence in cellular nuclei , is the generic name of the family of biopolymers. They are complex, high-molecular-weight biochemical macromolecules that can convey genetic information in all living cells and viruses. The most common nitrogenous bases are adenine , cytosine , guanine , thymine , and uracil. The nitrogenous bases of each strand of a nucleic acid will form hydrogen bonds with certain other nitrogenous bases in a complementary strand of nucleic acid similar to a zipper.
Adenine binds with thymine and uracil; thymine binds only with adenine; and cytosine and guanine can bind only with one another. Aside from the genetic material of the cell, nucleic acids often play a role as second messengers , as well as forming the base molecule for adenosine triphosphate ATP , the primary energy-carrier molecule found in all living organisms.
Glucose is an energy source in most life forms.
For instance, polysaccharides are broken down into their monomers by enzymes glycogen phosphorylase removes glucose residues from glycogen, a polysaccharide. Disaccharides like lactose or sucrose are cleaved into their two component monosaccharides. Glucose is mainly metabolized by a very important ten-step pathway called glycolysis , the net result of which is to break down one molecule of glucose into two molecules of pyruvate.
This does not require oxygen; if no oxygen is available or the cell cannot use oxygen , the NAD is restored by converting the pyruvate to lactate lactic acid e. Other monosaccharides like galactose and fructose can be converted into intermediates of the glycolytic pathway. In aerobic cells with sufficient oxygen, as in most human cells, the pyruvate is further metabolized. It is irreversibly converted to acetyl-CoA , giving off one carbon atom as the waste product carbon dioxide , generating another reducing equivalent as NADH. The two molecules acetyl-CoA from one molecule of glucose then enter the citric acid cycle , producing two molecules of ATP, six more NADH molecules and two reduced ubi quinones via FADH 2 as enzyme-bound cofactor , and releasing the remaining carbon atoms as carbon dioxide.
The produced NADH and quinol molecules then feed into the enzyme complexes of the respiratory chain, an electron transport system transferring the electrons ultimately to oxygen and conserving the released energy in the form of a proton gradient over a membrane inner mitochondrial membrane in eukaryotes.
This is why humans breathe in oxygen and breathe out carbon dioxide. 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 anaerobic metabolism , converting glucose to lactate.
The liver regenerates the glucose, using a process called 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. The combined pathways of glycolysis during exercise, lactate's crossing via the bloodstream to the liver, subsequent gluconeogenesis and release of glucose into the bloodstream is called the Cori cycle.
Researchers in biochemistry use specific techniques native to biochemistry, but increasingly combine these with techniques and ideas developed in the fields of genetics , molecular biology and biophysics. There is not a defined line between these disciplines. Biochemistry studies the chemistry required for biological activity of molecules, molecular biology studies their biological activity, genetics studies their heredity, which happens to be carried by their genome.
This is shown in the following schematic that depicts one possible view of the relationships between the fields: . Glucose and sucrose are also found in varying quantities in various fruits, and sometimes exceed the fructose present. However, peaches contain more sucrose 6. Oct, Vol. American Journal of Biomedical Sciences. From Wikipedia, the free encyclopedia. For the journals, see Biochemistry journal and Biological Chemistry journal.
Index Outline. Main article: History of biochemistry. Main articles: Composition of the human body and Dietary mineral. Main article: Biomolecule. Main articles: Carbohydrate , Monosaccharide , Disaccharide , and Polysaccharide. Glucose, a monosaccharide. Amylose , a polysaccharide made up of several thousand glucose units.
Main articles: Lipid , Glycerol , and Fatty acid. Main articles: Protein and Amino acid. Main article: Carbohydrate metabolism. Main article: Gluconeogenesis. Main article: Outline of biochemistry. Biochemistry portal. Important publications in biochemistry chemistry List of biochemistry topics List of biochemists List of biomolecules.
Trends in Biochemical Sciences. Molecular cell biology 4th ed. New York: Scientific American Books. Biochemistry 5th ed. W H Freeman. Genetics Home Reference. Retrieved 31 December Molecular Biology of the Cell, Sixth Edition. Garland Science. Amsler, Mark University of Delaware Press. Astbury, W. Bibcode : Natur. Ben-Menahem, Ari