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About 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium. All 11 are necessary for life.
An individual amino acid in a chain is called a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main chain or protein backbone. [36]: 19 The peptide bond has two resonance forms that confer some double-bond character to the backbone.
Ubiquitous, essential for all forms of life; all proteins and nucleic acids contain substantial amounts of nitrogen. [11] Toxic in some forms. [11] osmium: 76: 1a: None known. [11] Osmium is very rare, substantially more so than any element essential to life. [3] The oxide is toxic to humans. [11] oxygen: 8: 5
When two or more polypeptide chains (either of identical or of different sequence) cluster to form a protein, quaternary structure of protein is formed. Quaternary structure is an attribute of polymeric (same-sequence chains) or heteromeric (different-sequence chains) proteins like hemoglobin , which consists of two "alpha" and two "beta ...
At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]
Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids. Essential amino acids cannot be made by the animal. Some of the amino acids are ...
Both the α-helix and the β-sheet represent a way of saturating all the hydrogen bond donors and acceptors in the peptide backbone. Some parts of the protein are ordered but do not form any regular structures. They should not be confused with random coil, an unfolded polypeptide chain lacking any fixed three-dimensional structure.
The coordination sphere of the calcium ion contains only carboxylate oxygen atoms and no nitrogen atoms. This is consistent with the hard nature of the calcium ion. The protein has two approximately symmetrical domains, separated by a flexible "hinge" region. Binding of calcium causes a conformational change to occur in the protein.