Protein

 

Protein

A protein, colloquially known as egg white (outdated protein substance ), is a biological macromolecule made up of amino acids linked by peptide bonds.

Myoglobin was the first protein whose spatial structure was determined by crystal structure analysis

This globin serves as an oxygen store in muscle cells. Its peptide chain with α-helices, made up of more than 150 amino acids, folds into a spherical protein structure and holds a heme group on the iron atom of which O 2 can attach.

Proteins are found in every cell and usually make up more than half of the dry weight. They serve as molecular "tools" and, depending on the particular structure, perform different tasks by enabling cell movements, transporting metabolites, pumping ions, catalyzing chemical reactions, or recognizing signal substances. Muscles, heart, brain, skin, and hair also consist mainly of proteins.

 

The whole of all proteins in a living being, a tissue, a cell, or a cell compartment, under precisely defined conditions and at a certain point in time, is called a proteome.

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Word origin and history

The word protein was first used in 1839 in a publication by Gerardus Johannes Mulder. This designation was suggested to him in 1838 by Jöns Jakob Berzelius , who derived it from the Greek word πρωτεῖος proteins for 'fundamental' and 'primary,' based on FIRST photos for 'first' or 'more important.' This was based on the wrong idea that all proteins are based on a familiar primary substance. This resulted in a violent disagreement with Justus von Liebig.

 

The detail that proteins are made up of amino acid chains via peptide bonds was first suspected in 1902 at the 14th meeting of German naturalists and doctors, independent of Emil Fischer and Franz Hofmeister gave lectures. Fischer introduced the term peptide.

Protein biosynthesis

The building blocks of proteins are certain amino acids known as proteinogenic, i.e., protein-building, linked to chains by peptide bonds. There are 21 different amino acids in humans - the 20 known for a long time and selenocysteine. The human organism is mainly dependent on eight amino acids because they are essential, which means that the body cannot produce them itself but has to take them in with food. The amino acid chains can have a length of up to several thousand amino acids, amino acid chains with a length of less than about 100 amino acids being used as peptides and only speaks of proteins from a more considerable chain length. The molecular size is usually given in kilo-Daltons (kDa). Titin, the largest known human protein with approx. 3600 kDa, consists of over 30,000 amino acids and contains 320 protein domains.

 

The amino acid sequence of a protein - and thus its structure - is encoded in deoxyribonucleic acid (DNA). The genetic code used for this has hardly changed during the evolution of living things. In the ribosomes, the cell's "protein production machinery," this information is used to assemble a polypeptide chain from individual amino acids, whereby the amino acids determined by a codon are linked in the sequence specified by DNA. Only with this chain's folding in an aqueous cell environment, the three-dimensional shape then produced a specific protein molecule.

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The haploid human genome contains around 20,350 protein-coding genes - much fewer than assumed before the genome was sequenced. Only about 1.5% of total genomic DNA encoding proteins, while the rest of the genes for non-coding RNA and introns, regulatory DNA, and non-coding deoxyribonucleic consist.  Since many of the protein-coding genes - for example, through alternative splicing of the primary transcript ( precursor mRNA) of a gene - producing more than one protein, there are far more than just 20,350 different proteins in the human body. We now know proteins whose formation goes back to exons of genes or gene segments in spatially distant chromosome regions, sometimes even different chromosomes.  The traditional one-gene-one-enzyme hypothesis (also: one-gene-one mRNA -one protein hypothesis) is no longer tenable for higher organisms today.

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