Chains and Chain IDs
From Proteopedia
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Each protein chain has '''two ends''', an amino terminus (positively charged) and a carboxy terminus (negatively charged). The first residue in a protein chain becomes the amino terminus, with new amino acids being added at the carboxy terminus. The sequence of [[amino acids]] is specified by messenger RNA, which is a copy of the sequence of codons in the template strand of the DNA gene. The first residue in a nucleic acid chain becomes the 5' (phosphate) terminus, with new nucleotides being added at the 3' (hydroxy) terminus. | Each protein chain has '''two ends''', an amino terminus (positively charged) and a carboxy terminus (negatively charged). The first residue in a protein chain becomes the amino terminus, with new amino acids being added at the carboxy terminus. The sequence of [[amino acids]] is specified by messenger RNA, which is a copy of the sequence of codons in the template strand of the DNA gene. The first residue in a nucleic acid chain becomes the 5' (phosphate) terminus, with new nucleotides being added at the 3' (hydroxy) terminus. | ||
| - | Protein molecules may consist of one or more polypeptide chains. Those with more than one chain may be termed homo-oligomers or hetero-oligomers, homo-multimers or hetero-multimers. The functional form of the molecule, termed the [[biological unit]], often contains a different number of chains than does the crystallographic [[asymmetric unit]]. Examples are given in the article on [[biological units]]. | + | Protein molecules may consist of one or more polypeptide chains (see [[Protein primary, secondary, tertiary and quaternary structure]]. Those with more than one chain may be termed homo-oligomers or hetero-oligomers, homo-multimers or hetero-multimers. The functional form of the molecule, termed the [[biological unit]], often contains a different number of chains than does the crystallographic [[asymmetric unit]]. Examples are given in the article on [[biological units]]. |
In a protein molecule consisting of multiple chains, the chains are usually held together by non-covalent bonds, but sometimes by covalent bonds, usually [[disulfide bonds]]. See [[Protein primary, secondary, tertiary and quaternary structure|quaternary structure]]. | In a protein molecule consisting of multiple chains, the chains are usually held together by non-covalent bonds, but sometimes by covalent bonds, usually [[disulfide bonds]]. See [[Protein primary, secondary, tertiary and quaternary structure|quaternary structure]]. | ||
Revision as of 01:36, 11 February 2025
The term chain, in biochemistry, usually denotes either a polypeptide chain or a polynucleotide chain.
- Protein Chains: A polypeptide chain is a sequence of amino acids covalently linked by peptide bonds. When longer than 50 amino acids, it is called a Protein, whereas a short polypeptide consisting of 50 or fewer amino acids is termed a peptide. The chain structures of proteins are most easily visualized with backbone representations.
- Nucleic Acid Chains: A polynucleotide chain is a sequence of nucleotides covalently linked by ribose (or deoxyribose)-phosphodiester bonds, e.g. either DNA or RNA.
Polypeptide (protein) chains are linear, with rare exceptions where side-chains form protein crosslinks between two linear chains, such as disulfide bonds, or less commonly other types protein crosslinks of such as isopeptide bonds.
Each protein chain has two ends, an amino terminus (positively charged) and a carboxy terminus (negatively charged). The first residue in a protein chain becomes the amino terminus, with new amino acids being added at the carboxy terminus. The sequence of amino acids is specified by messenger RNA, which is a copy of the sequence of codons in the template strand of the DNA gene. The first residue in a nucleic acid chain becomes the 5' (phosphate) terminus, with new nucleotides being added at the 3' (hydroxy) terminus.
Protein molecules may consist of one or more polypeptide chains (see Protein primary, secondary, tertiary and quaternary structure. Those with more than one chain may be termed homo-oligomers or hetero-oligomers, homo-multimers or hetero-multimers. The functional form of the molecule, termed the biological unit, often contains a different number of chains than does the crystallographic asymmetric unit. Examples are given in the article on biological units.
In a protein molecule consisting of multiple chains, the chains are usually held together by non-covalent bonds, but sometimes by covalent bonds, usually disulfide bonds. See quaternary structure.
