The genetic code is a set of three-nucleotide sets called codons and each three-nucleotide combination designates an amino acid, for example aug ( adenine - uracil - guanine ) is the code for methionine. Because dna contains four nucleotides, the total number of possible codons is 64; hence, there is some redundancy in the genetic code, with some amino acids specified by more than one codon. 14 Genes encoded in dna are first transcribed into pre- messenger rna (mRNA) by proteins such as rna polymerase. Most organisms then process the pre-mrna (also known as a primary transcript ) using various forms of Post-transcriptional modification to form the mature mrna, which is then used as a template for protein synthesis by the ribosome. In prokaryotes the mrna may either be used as soon as it is produced, or be bound by a ribosome after having moved away from the nucleoid. In contrast, eukaryotes make mrna in the cell nucleus and then translocate it across the nuclear membrane into the cytoplasm, where protein synthesis then takes place. The rate of protein synthesis is higher in prokaryotes than eukaryotes and can reach up to 20 amino acids per second.help
For instance, yeast cells have been estimated to contain about 50 million proteins and human cells on the order of 1 to 3 billion. 10 The concentration of individual protein copies ranges from a few molecules per cell up to 20 million. 11 Not all genes coding proteins are expressed in most cells and their number depends on, for example, cell type and external stimuli. For instance, of the 20,000 or so proteins encoded by the human genome, only 6,000 are detected in lymphoblastoid cells. 12 Moreover, the number of proteins the genome encodes correlates well with the organism complexity. Eukaryotes, bacteria, archaea and viruses have on average 15145, 3200, 2358 and 42 proteins respectively coded in their genomes. 13 Synthesis biosynthesis A ribosome produces a protein using mrna as template main article: Protein biosynthesis Proteins are assembled from amino acids using information encoded in genes. Each protein has its own trunk unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein.
The words protein, polypeptide, and peptide are a little ambiguous and can overlap in meaning. Protein is generally used to refer to the complete biological molecule in a stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often lacking a stable three-dimensional structure. However, the boundary between the two is not well defined and usually lies near 2030 residues. 5 Polypeptide can refer to any single linear chain of amino acids, usually regardless of length, but often implies an absence of a defined conformation. Interactions Proteins can interact with many types of molecules, including with other proteins, with lipids, with carboyhydrates, and with dna. 6 7 8 9 Abundance in cells It has been estimated that average-sized bacteria contain about 2 million proteins per cell (e.g. Coli and Staphylococcus aureus ). Smaller bacteria, such as Mycoplasma or spirochetes contain fewer molecules, on the order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus contain much more protein.
Protein, synthesis -Translation and Regulation
Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, x-ray crystallography, nuclear magnetic resonance and mass spectrometry. Contents biochemistry Chemical structure of the assignment peptide bond (bottom) and the three-dimensional structure of a peptide bond between an alanine and an adjacent amino acid (top/inset). The bond itself is made of the chon elements. Main articles: biochemistry, amino acid, and Peptide bond Most proteins consist of linear polymers built from series of up to 20 different l-α- amino acids. All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this basic structure as it contains an unusual ring to the n-end amine group, which forces the conh amide moiety into a fixed conformation.
1 The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines. 2 The amino acids in a polypeptide chain are linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called a residue, and the linked series of carbon, english nitrogen, and oxygen atoms are known as the main chain or protein backbone. 3 The peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar. The other two dihedral angles in the peptide bond determine the local shape assumed by the protein backbone. 4 The end with a free amino group is known as the n-terminus or amino terminus, whereas the end of the protein with a free carboxyl group is known as the c-terminus or carboxy terminus (the sequence of the protein is written from N-terminus.
Shortly after or even during synthesis, the residues in a protein are often chemically modified by post-translational modification, which alters the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a certain period and are then degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of its half-life and covers a wide range.
They can exist for minutes or years with an average lifespan of 12 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized. Digestion breaks the proteins down for use in the metabolism. Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, and chromatography ; the advent of genetic engineering has made possible a number of methods to facilitate purification.
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Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, dna replication, responding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity. A twist linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 2030 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded essay together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids; however, in certain organisms the genetic code can include selenocysteine and—in certain archaea — pyrrolysine.
of molecules. For protein as a nutrient, see. For other uses, see, protein (disambiguation). A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. This protein was the first to have its structure solved. Towards the right-center among the coils, a prosthetic group called a heme group (shown in gray) with a bound oxygen molecule (red). Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues.
The process of transcription, transcription takes place in the nucleus: the gene coding for the protein required untwists then unzips, the h-bonds between the strands break free rna nucleotides form complementary base pairs base pair : The pair of nitrogenous bases that connects the complementary. with one strand of dna bases weak hydrogen bonds form between base pairs sugar phosphate bonds form between rna nucleotides mrna strand is synthesized mrna peels off the dna and moves out of the nucleus into the cytoplasm. The process of translation, translation takes place on the ribosomes in the cytoplasm, or found on the rough Endoplasmic Reticulum (er the ribosomes are the sites of protein synthesis the mrna strand attaches to a ribosome trna molecules molecules : a collection of two. The fundamental unit strange of compounds transport specific amino acids to the ribosome each mrna codon codes for a specific amino acid the anti-codons and codons match up and form complementary base pairs peptide bonds form between the adjacent amino acids to form the polypeptide. Once the protein has been synthesised synthesised : made or put together mrna may move to another ribosome to make a further protein or it can be broken down into free nucleotides to be reused. Processing the proteins After translation, the protein passes into the channels of the rough endoplasmic reticulum (ER) for transportation. The protein is then passed from the rough er to the golgi apparatus inside tiny fluid-filled sacs, called vesicles. The golgi apparatus is a system of membranes membrane : a very thin layer of tissue, which are responsible for the modification, processing, and packaging of the proteins.
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The following factors must be present for dna replication replication : Production of an identical copy. and transcription: gene (DNA) to act as a template supply of free rna nucleotides enzymes, atp, the base sequence in a dna molecule, represented by the letters. g, make up the genetic code. The bases hydrogen bond together in a complementary manner between strands. A will always go with T (U in rna) and G will always go with. This code determines the type of amino acids and the order in which they are joined together to make a specific protein. The sequence of amino acids in a protein determines its structure and function. The dna code is resume a triplet code triplet code : the genetic code made by a triplet of bases in the dna chains: aaa; gct; cat etc. Each triplet, a group of three bases, codes for a specific amino acid: the triplet of bases on the dna and mrna is known as a codon the triplet of bases on the trna is known as an anti-codon, the main stages of protein synthesis.