All about proteins

A protein is a biological macromolecule composed of one or more chains of amino acids linked by peptide bonds (polypeptide chain). In general, one speaks of protein when the string contains at least 100 implicated acids and peptide for smaller assemblies.
Proteins are essential elements of the life of the cell: they can play a structural role (such as actin), a role in mobility (such as myosin), a catalytic role (enzymes), a role of regulation of compaction (transcription factor) gene expression and DNA (histones), etc. In short, the vast majority of cellular functions are carried out by proteins.
The structure of proteins is complex and affects the role they play in the life of the cell.
haemoglobin

Three-dimensional image, after computer processing to represent the structures of the different levels of organizations of chains of amino acids of a protein, these strings are coiled and folded on themselves.
Above a modeling of the 3D structure of haemoglobin in humans.

History

Proteins were discovered from 1835 in the Netherlands by the chemist Johannes Gerardus Mulder2 (1802-1880), under the name of wortelstof. In his illustrious Swedish colleague, Jöns Jacob Berzelius, who suggested in 1838 the name of protein.
The word protein comes from the Greek former protos meaning first, essential. This probably refers to the fact that proteins are essential to life and it is often the majority share (approx. 60%) of the dry weight of cells. Another theory, would like to that protein should refer, as the adjective protean, to the Greek god Proteus who could change shape at will. Proteins are in fact multiple forms and perform multiple functions. But this was discovered until much later, during the twentieth century.

Synthesis

Proteins are assembled from amino acids based on the information contained in the genes. Their synthesis is done in two steps:
The transcript where the sequence of DNA encoding the gene associated with the protein is transcribed into messenger RNA
The translation where the messenger RNA is translated into protein, ribosome level, based on the genetic code
The Assembly of a protein is therefore amino acid by amino acid N-terminal to its C-terminus. After its synthesis by the ribosome, the protein can undergo post-translational modifications, cleavages, maturations. Finally, in some organisms of the alternative messenger RNA Splicing process can result in the production of several different forms of a protein from the same gene.

Proteome

Beginning of 2012, more than 3000 genomes of living organisms have been sequenced and more than 7000 are under sequencing.
The genomes of model organisms key such as the bacterium Escherichia coli, the Yeast Saccharomyces cerevisiae, the plant Arabidopsis thaliana and many other genomes which that having been decrypted, it is recognized that almost all of the genes could be set.
By against the inventory of active proteins (proteome) in an organization is far from being established. Indeed, because of the variability of the process of activation and regulation of proteins, this inventory is not the result of the simple translation of each gene that would give an active protein: for example some genes can give several different forms of a protein, or proteins must be modified to be active.

Structure

The proteins are molecular objects whose description introduces the concept of structures (in a more or less hierarchy).
For the first time in 1957, John Kendrew and Max Perutz, crystallography and x-ray diffraction, were able to describe the structure in three dimensions of Myoglobin and hemoglobin.
The function of the proteins is conferred by their three-dimensionality, that is the way structure in which amino acids are arranged to each other in space. This is the reason why the methods for the determination of the three-dimensional structures as well as measures of the dynamics of proteins are important and is a lookup field from very asset. In addition to these experimental methods, many studies focus on computational methods of 3D from the sequence structure prediction.
The order in which the amino acid chain is encoded by the genome and is the primary structure of the protein. The protein folds back on itself to form secondary structures, of which the most important quantitatively is the alpha helix and the beta sheet, allowing you to create links h-bonding between atoms of carbon and nitrogen of two neighboring peptide bonds. Then, the various secondary structures are arranged each other to form tertiary structure, often enhanced by disulfide bridges. The forces that govern this folding is the classic physical forces. In the case of proteins through the combination of several channels, the Quaternary structure describes the relative position of the subunits each other.
There are several chaperone proteins that facilitate, or are required, to the folding of proteins to the active state. Protein folding is the subject of intense research in the field of structural biology, combining the Molecular Biophysics and cell biology techniques mainly.

Functions

Proteins perform functions very different within the cell and the organism:
structural proteins, which allow the cell to keep his organization in the space. They are the constituents of the cytoskeleton
transport proteins that transfer of the different molecules in and out of cells
regulatory proteins which modulate the activity of other proteins or that control the expression of genes
signaling proteins that capture the external signals and ensure their transmission in the cell or the organism, there are
several kinds
+ for example: hormonal proteins, which help to coordinate the activities of an organization acting as signals between cells.
receptor proteins: detect Messenger molecules and other signals that the cell act accordingly.
+ sensory proteins, they detect environmental signals (ex: light) and respond to signals in the cell.
+ hormone receptors, they detect the hormones and send signals to the cell so that it acts as a result (ex: insulin is a hormone that when she is about to be captured, will report to the cell to absorb and use the sugar)
motor proteins, allowing the cells or organisms or elements (lashes) of move or deform (ex: actin and myosin allows the muscle to contract)
the defense proteins, protecting the cell from viruses (ex: antibodies)
storage proteins, allowing storage of amino acids to be able to create other proteins
enzymes, they change the speed of almost all chemical reactions in the cell without be transformed in the reaction

Phenotype

Protein manufacturing plan depends in the first place of the gene. However the sequences of the genes are not identical from one individual to another. For more, in the case of human beings living diploid, there are two copies of each gene. And these two examples are not necessarily identical. A gene is in several versions of an individual to the other, and sometimes in the same individual. These versions are called alleles. The set of alleles an individual forms genotype.
Since genes exist in several versions, the proteins will also exist in different versions. These different versions of proteins will cause differences from one individual to another: such an individual will have blue eyes but another will have black eyes, etc. These characteristics, visible or not, specific to each individual are referred to as the phenotype. In the same individual, a group of proteins with similar sequence and re-assigning says isoform. The isoforms can be the result of alternative splicing of the same gene, the expression of several alleles of a gene, or the presence of several homologous genes in the genome.

Evolution

During evolution, the accumulations of mutations made diverge genes within species and between species. Thence comes the diversity of proteins that are associated with them. One can however define protein families, themselves belonging to families of genes. Thus, in a species can coexist genes and therefore very similar proteins forming a family. Two closely related species are likely to have representatives of same family of proteins.
Talking of homology between proteins when different proteins have a common origin, a common ancestral gene.
Protein sequence comparison allows to highlight the degree of ‘relationship’ between different proteins, one speaks here of sequence similarity. The function of the proteins can diverge that similarity decreases, thus giving birth to families of proteins having a common origin but with different functions.
Protein structures and sequences analysis identified that many organized into domains, that is, parties acquiring a structure and performing a specific function. The existence of multidomain proteins can be the result of recombination in a single gene of several originally individual genes and conversely proteins consisting of a single domain can be the result of multiple genes from a gene originally separation encoding a protein in several areas.

Food

In nutrition, proteins are disaggregated during digestion from the stomach. It is there that the proteins are hydrolyzed by proteases and cut into polypeptides to then provide amino acids for the organism, including those so-called essential, that the body is unable to synthesize. Pepsinogen is converted to pepsin when it comes in contact with hydrochloric acid. Pepsin is the only proteolytic enzyme which digests collagen, the main protein of connective tissue. The major part of digestion of proteins takes place in the duodenum.
Almost all proteins are absorbed when they arrive in the jejunum and only 1% of the ingested proteins are found in the feces. Some amino acids remain in epithelial cells and are used for the synthesis of new proteins, including some intestinal proteins, constantly digested, recycled and absorbed by the small intestine.

The body-mass-index (BMI)

The body-mass-index (BMI)  – is a measure of the evaluation of the body weight of a person in relation to his height. It was developed in 1832 by Adolphe Quetelet.
The BMI refers to the body mass (or mass, colloquially known as weight) on the square of the height. The value “Square of height” is unrelated to the surface of the body. BMI is only a rough guideline, since he considered stature and gender, nor the individual composition of body fat and muscle tissue of a person.
General calculation formula
The body mass index is calculated as follows:

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where the body mass (in kilograms) and height is (in meters).
Calculation of missing limbs (amputation)
There is an amputation, so you must calculate mt the theoretical body mass prior to the calculation of BMI:
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For this, the following values are used:
Body correction factor k
Hand 0.008
Forearm 0.023
Upper arm 0.035
Foot 0.018
Lower leg 0.053
Thigh 0,116
Example
A woman was 56 kilograms, 20 years old and 1.70 m tall. Amputated the left leg of the woman, which is why the correction values for a lower leg and foot (logically also removed by amputation of the lower leg) are to apply. Their theoretical weight calculated thus as follows:
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This mass can then be used in the normal BMI formula:
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interpretation
in adults
Values of normal-weight people are m² and 24.99 kg / m² in accordance with WHO’s obesity classification between 18.5 kg / m sq, from a BMI of 30 kg / m obese individuals considered sq in need of treatment.
Age and gender play a major role in the interpretation of the BMI. Men have typically a higher percentage of muscle mass to the total body mass than women. Therefore, the lower and upper bounds of the BMI value classes when men are slightly higher than for women. So the normal weight is according to the DGE men ranging from 20 to 25 kg / m, while women inside ranging from 19 to 24 kg / m².
The Broca’s index is used for the assessment of an underweight such as anorexia. The diagnostic criteria of anorexia in adults a BMI ≤ 17.5 kg / m² provide in children and adolescents a BMI below the 10th percentile of the age.
Examples
A woman weighs 58 kg and 1.70 m tall. Your BMI is calculated as follows: 58 kg / (1.7 m · 1.7 m) ≈ 20 kg / m² ⇒ normal weight.
A man is 87 kilograms and is 1.76 m tall. His BMI is calculated as follows: 87 kg / (1.76 m · 1.76 m) ≈ 28 kg / m² ⇒ overweight.
in children
The BMI can be used also for children and infants as a measure for the healthy development of the child. The BMI is calculated using the same formula as the BMI of adults, however, the length lying down rather than the level of the standing is used in children less than 25 months. This may be up 0.7 cm longer than the height in the standing position, therefore the normal BMI range have a characteristic kink here in the tables. The child’s BMI is compared in the tables with the data of other children of same age. WHO publishes the BMI tables for boys and  girl. A child with more than + 1 is considered as overweight standard deviation SD (corresponding to a BMI of over 25 in an adult), of whom are obese with more than + 2 SD (corresponding to a BMI of more than 30 in an adult). For children under the age of five, there are corresponding tables of the WHO.
A further possibility to calculate is so-called Percentile curve to go to, where is the ideal BMI on the average of the existing values. The child is considered of whom are obese, if it has a higher BMI than 97% (97. Alters percentage) his peers, underweight, when only 3% (3. Alters percentage) or less have a lower BMI.
The problem of this calculation basis is that that the definition for malnutrition would move, if changed the nutritional status of children in a society as a whole, for example through a famine, many children are undernourished, or if there are many overweight children. If by definition always exactly 15% of all children are overweight, you can’t get for example to say, 25% of all children are overweight.
The limits of an appropriate BMI strongly relate to the level of development of the child. So, for example, the rapid growth in the early stages of puberty and the like is shown. A child makes these stages earlier or later than the average, with also an according to the age group is too high or too low BMI can occur despite normal weight.
Validity
The use of BMI for the diagnosis of underweight or body fat fat induced obesity based on defined limits is very controversial. Because a relatively high body weight and thus a high BMI may be caused also by much muscle mass. Trained strength athlete without much body fat have a high BMI alone due to their lean muscle mass. Athletes of endurance (5 km run, 10 km run, Marathon), who participated in the Olympics in 1960 in Rome, have a BMI of 20-21, a BMI of 26-29  therefore the scale of what is considered normal weight, is adapted for the medical diagnosis of bottom and overweight if necessary strength athletes (weightlifting, Javelin, hammer and discus, shot putter). So, a reduction in the limit between normal and overweight by 30 kg / m2 to 22 kg / m2 was found, for example, for paraplegia.
In anthropometric history and historical anthropology of the average body-mass index of populations is similar to the height, used as indicator for the standard of living. Based on historical data collected such as the recruit patterns possible reviews in the past. Times past in next return estimates of BMI, which were conducted on bones from archaeological contexts. To them can be estimated, that the average diet in the early Middle Ages in Europe was quite good.
BMI of athletes. Sport; n: number of observations; medium height, weight and BMI.
History
The BMI was developed in 1832 by Belgian mathematician Adolphe Quetelet. The term body mass index (BMI) is a 1972 published article of Ancel keys. Keys recommended BMI only for the statistical comparison of populations, not for the assessment of overweight individuals. Through the use of BMI, meaning won U.S. life insurers who use this simple classification, so to calculate premiums for life insurance, that additional risks are taken into account by overweight. Since the early of 1980s, the BMI is used also by the World Health Organization WHO. The present BMI classification WHO is essentially since 1995.
The body-mass index as a criterion for the verb appointment in the public service will be used in some German Länder (Baden-Württemberg and North Rhine-Westphalia, for example). People with too high or too low BMI are not established. This arrangement was criticized in several times.
Other indexes
A number of other indexes exist in addition to the BMI. The Broca’s index and the Ponderal index are the most famous. The physique development index is suitable even for a biological age determination.
An eight-year study of the Munich Ludwig-Maximilians-University with over 11,000 subjects according to the relationship between waist circumference and height (“waist-to-height ratio”, waist–hip) is better suited for the assessment of health risks because here more accurate conclusions on the health concern belly fat can be drawn.
The WHR (waist-hip ratio, waist-to-hip ratio), which was originally introduced as a first and foremost body aesthetic measure also allows an assessment of the distribution of body fat. Another dimension is the surface of the body, often using the Mosteller formula calculated. As a result of this many mass being classified as overweight for the same person – varies depending on the total length and morphology – according to the formula of one or the other. As a more commercially-oriented, so-called vital analyses are to see.
The area is a further development of the BMI mass index (AMI), which takes into account the stature and the sex of an individual. Makes it easy to measure the waist circumference. He correlates well with the BMI and is therefore, in medicine and in the population often used to determine obesity.
Body adiposity index
The body adiposity index (BAI) is a method different from the body-mass index of to calculated or estimated the percentage of body fat. BAI takes into account also the hips as well as the length of the body. According to a study by 2012 of the Institute for nutritional research in Potsdam-Rehbrücke and the medical clinic IV of the University of Tübingen (the data of the Tübingen lifestyle of intervention program – TULIP – were used) he is now inferior until 2011 popular BAI BMI in its significance, because the BMI in a closer relationship to the distribution of body fat as the BAI – especially for men. The measured waist circumference, however, has a still higher significance about the body fat percentage as the BMI or BAI. Diabetes risk assessment of BMI was superior to the BAI, however, the waist had again a still higher significance again. BAI fails thus as an alternative to the BMI into consideration. Therefore, the measurement of the waist as a supplement to the determination of BMI is useful.
The BAI is calculated according to the formula:
BAI = (waist circumference in cm) / (m size) 1.5 − 18