PLOS ONE: Improved Cell-Free RNA and Protein Synthesis …
Proteins are assembled from amino acids using information encoded in genes
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The next level of protein structure is called the secondary structure. The side chains of the residues have various functional groups that can have different types of forces: some are hydrophobic and others are hydrophilic ; some participate in hydrogen bonding interactions while others do not. These forces lead to conformations (geometric arrangements of the residues) that result in lower energies. Two specific arrangements that are found regularly are shown in Figure 2: a helix (which looks like a corkscrew) and a pleated sheet (which looks like a paper that has been folded and opened).
Nutrition Diva reader Thomas writes:
"Some people claim that the body can't absorb more than 20-30 grams of protein at a time. Others insist that your body utilizes all the protein you take in. Who is right? Is a post-workout shake with 50 grams of protein a waste?"
This idea that the body can only utilize a certain amount of protein at one sitting has become widely accepted nutrition lore. But is there any validity to the claim? It all comes down to what exactly you mean by "utilizing" protein.
This notion about protein seems to have gotten started on body-building forums - and this may be the main source of some of the confusion. Body-builders are particularly interested in protein's ability to build and repair muscles. And there does seem to be a limit to how much protein the body can use for muscle synthesis at a given time.
protein synthesis | Health & Nutrition Articles
Within our bodies and those of other living organisms, proteins serve many functions. They digest foods and turn them into energy; they move molecules about within our cells; they let some substances pass through cell membranes while keeping others out; they turn light into chemical energy, making both vision and photosynthesis possible; they allow cells to detect and react to hormones and toxins in their surroundings; and they protect our bodies against foreign invaders.
protein, any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight. Hundreds of protein molecules have been isolated in pure, homogeneous form; many have been crystallized. All contain carbon, hydrogen, and oxygen, and nearly all contain sulfur as well. Some proteins also incorporate phosphorous, iron, zinc, and copper. Proteins are large molecules with high molecular weights (from about 10,000 for small ones [of 50–100 amino acids] to more than 1,000,000 for certain forms); they are composed of varying amounts of the same 20 , which in the intact protein are united through covalent chemical linkages called bonds. The amino acids, linked together, form linear unbranched polymeric structures called polypeptide chains; such chains may contain hundreds of amino-acid residues; these are arranged in specific order for a given species of protein.
Types of Proteins
A protein molecule that consists of but a single polypeptide chain is said to be monomeric; proteins made up of more than one polypeptide chain, as many of the large ones are, are called oligomeric. Based upon chemical composition, proteins are divided into two major classes: simple proteins, which are composed of only amino acids, and conjugated proteins, which are composed of amino acids and additional organic and inorganic groupings, certain of which are called . Conjugated proteins include , which contain carbohydrates; , which contain lipids; and nucleoproteins, which contain .
Classified by biological function, proteins include the , which are responsible for catalyzing the thousands of chemical reactions of the living cell; , elastin, and , which are important types of structural, or support, proteins; and other gas transport proteins; ovalbumin, , and other nutrient molecules; , which are molecules of the immune system (see ); protein , which regulate ; and proteins that perform mechanical work, such as and , the contractile muscle proteins.
Every protein molecule has a characteristic three-dimensional shape, or conformation. Fibrous proteins, such as collagen and keratin, consist of polypeptide chains arranged in roughly parallel fashion along a single linear axis, thus forming tough, usually water-insoluble, fibers or sheets. Globular proteins, e.g., many of the known enzymes, show a tightly folded structural geometry approximating the shape of an ellipsoid or sphere.
Because the physiological activity of most proteins is closely linked to their three-dimensional architecture, specific terms are used to refer to different aspects of protein structure. The term primary structure denotes the precise linear sequence of amino acids that constitutes the polypeptide chain of the protein molecule. Automated techniques for amino-acid sequencing have made possible the determination of the primary structure of hundreds of proteins.
The physical interaction of sequential amino-acid subunits results in a so-called secondary structure, which often can either be a twisting of the polypeptide chain approximating a linear helix (α-configuration), or a zigzag pattern (β-configuration). Most globular proteins also undergo extensive folding of the chain into a complex three-dimensional geometry designated as tertiary structure. Many globular protein molecules are easily crystallized and have been examined by X-ray diffraction, a technique that allows the visualization of the precise three-dimensional positioning of atoms in relation to each other in a crystal.
The tertiary structure of several protein molecules has been determined from X-ray diffraction analysis. Two or more polypeptide chains that behave in many ways as a single structural and functional entity are said to exhibit quaternary structure. The separate chains are not linked through covalent chemical bonds but by weak forces of association.
The precise three-dimensional structure of a protein molecule is referred to as its native state and appears, in almost all cases, to be required for proper biological function (especially for the enzymes). If the tertiary or quaternary structure of a protein is altered, e.g., by such physical factors as extremes of temperature, changes in H, or variations in salt concentration, the protein is said to be denatured; it usually exhibits reduction or loss of biological activity.
The cell's ability to synthesize protein is, in essence, the expression of its genetic makeup. Protein synthesis is a sequence of chemical reactions that occur in four distinct stages, i.e., activation of the amino acids that ultimately will be joined together by peptide bonds; initiation of the polypeptide chain at a cell organelle known as the ribosome; elongation of the polypeptide by stepwise addition of single amino acids to the chain; and termination of amino-acid additions and release of the completed protein from the ribosome. The information for the synthesis of specific amino-acid sequences is carried by a nucleic acid molecule called messenger RNA (see ). Proteins are needed in the diet mainly for their amino acids, which the body uses to build new proteins (see ).
The mechanism of action of many widely used antibiotics, such as , , and , can be understood in terms of their ability to interfere with some stage of protein synthesis in bacteria.
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The order of the amino acids in a protein dictates the primary structure of the protein. While other levels of structure are important, they all follow from the order of the residues. The primary structure is dictated by genetic information found in a cell; deoxyribonucleic acid (DNA ) contains the code that directs which amino acids are linked together. The processes by which the genetic code is read and proteins are synthesized are called transcription and translation.
Some proteins, including a number of hormones, have only a relatively small number of amino acid units, while others have literally thousands. Once an amino acid is incorporated into the polypeptide, it is referred to as a residue. When biochemists identify a particular portion of a protein, they usually refer to the residue with its name and a number, referring to how far from the N-terminus that residue is located.
Journal of the American Chemical Society (ACS …
All about protein: What is it and how much do you need?
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29/11/2017 · Leucine Regulates Translation Initiation of Protein Synthesis ..
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Protein - Wikipedia
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Most proteins are structurally altered after synthesis through chemical modification or processing. These alterations help the cell determine a protein's fate, such as whether that protein is active or inactive, how long the protein will function, and to some degree the location where that protein will function. Chemical modifications, which are additions of chemical groups to the R groups in the amino acids, are made after translation. Such modifications may include the attachment of a phosphate group (phosphorylation) to the alcohol group on the amino acids of serine, threonine, or tyrosine. The amino acid proline in proteins such as collagen is often hydroxylated, which means that an alcohol group is attached. Other amino acids with amino groups in their R region, such as lysine or arginine, may be chemically modified through methylation, which is the addition of a methyl group (-CH3), or through acetylation, in which an acetyl group (-CH3CO) is added. Larger modifications, such as the addition of a carbohydrate group, occur to create glycoproteins in specialized organelles termed Golgi apparati.
Collagen: What is it and what are its uses? - Health News
Proteins targeted for internal cellular functions are synthesized on ribosomal assemblages that float free in the cytoplasm. Such proteins also have their signal sequences. Proteins destined for the cell's nucleus have a specific nuclear signal sequence consisting of a small series of basic amino acids such as arginine and lysine bounded by proline. This nuclear signaling sequence can be located anywhere in the protein's sequence as long as it projects outward from the three-dimensional tertiary structure. Signal sequences for proteins targeted to be part of organelles such as the mitochondriaand chloroplasts are anywhere from twenty to seventy amino acids long and are mostly hydrophilic. This charged nature allows easy travel through the hydrophilic cytoplasm to the organelle.
RCSB Protein Data Bank - RCSB PDB
Protein must be delivered to the proper destination in the cell to function properly. Signal sequences within the protein itself act like "zip codes" to ensure correct delivery. The synthesis of secreted proteins like insulin and of proteins that will be integral to the plasma membrane occurs at a ribo-some tethered to the endoplasmic reticulum , which is a system of membranes that transport materials within cells. The peptides formed there are then translocated into the lumen , or channel, of the endoplasmic reticulum, where they will be formed into a polypeptide chain. This translocation occurs because of a specific signal sequence that is formed by the first twenty or so amino acids in the protein. The core of this sequence consists of ten to fifteen amino acids that have hydrophobic side chains such as alanine, leucine, valine, isoleucine, and phenylalanine, which are usually cleaved from the protein later on. The nascent polypeptide chain is guided along this path by a signal receptor protein.
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