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Tue Nov 17, 2015 1:19 am
The wide variety of 3-dimensional protein structures corresponds to the diversity of functions proteins fulfill. Proteins fold in three dimensions.protein expression in bacteria is organized hierarchically from so-called primary structure to quaternary structure. Higher-level structures are motifs and domains. Above all the wide variety of conformations is due to the huge amount of different sequences of amino acid residues.
1. Primary structure
The primary structure is the sequence of residues in the polypedptide chain. The primary level of protein structure is not just the number and identity of the component amino acids in the protein, but the order or sequence in which the specific amino acids are combined (by condensation, forming peptide bonds) in the polypeptide chain.
2. Secondary structure
The polypeptide chain can fold back on itself in a number of ways. Each bond in the backbone formed by alternating amino acid central carbons and -CONH - peptide linkages can rotate completely, and so a number of shapes are possible.
It will become stabilised in a position where >NH groups (from the peptide bonds) become close enough to form hydrogen bonds with >C=O groups on another peptide bond, in another chain, or further along in the same chain.
3. Tertiary structure
The 3-dimensional structure of a protein's polypeptide chain or chains may be locked in place by other stronger bonds. These bonds are formed between components of the -R groups of the amino acid residues.
4. Quaternary structure (Not all proteins have a quaternary level of structure)
A protein with a quaternary structure consists of more than one practically identical sub-unit, not joined by strong bonds like those above.
A well known example is haemoglobin, which consists of 2 alpha and 2 beta chains, consisting of 141 and 142 amino acid residues respectively.
Many enzymes consist of several sub-units, often as dimers (2 sub-units) and tetramers (4 sub-units) combined in this way.
Tertiary structure
Quaternary structure
1. Primary structure
The primary structure is the sequence of residues in the polypedptide chain. The primary level of protein structure is not just the number and identity of the component amino acids in the protein, but the order or sequence in which the specific amino acids are combined (by condensation, forming peptide bonds) in the polypeptide chain.
2. Secondary structure
The polypeptide chain can fold back on itself in a number of ways. Each bond in the backbone formed by alternating amino acid central carbons and -CONH - peptide linkages can rotate completely, and so a number of shapes are possible.
It will become stabilised in a position where >NH groups (from the peptide bonds) become close enough to form hydrogen bonds with >C=O groups on another peptide bond, in another chain, or further along in the same chain.
3. Tertiary structure
The 3-dimensional structure of a protein's polypeptide chain or chains may be locked in place by other stronger bonds. These bonds are formed between components of the -R groups of the amino acid residues.
4. Quaternary structure (Not all proteins have a quaternary level of structure)
A protein with a quaternary structure consists of more than one practically identical sub-unit, not joined by strong bonds like those above.
A well known example is haemoglobin, which consists of 2 alpha and 2 beta chains, consisting of 141 and 142 amino acid residues respectively.
Many enzymes consist of several sub-units, often as dimers (2 sub-units) and tetramers (4 sub-units) combined in this way.
Tertiary structure Quaternary structure