The Covalent Structure of Proteins:- Amino Acid Sequences Provide Important Biochemical Information

Knowledge of the sequence of amino acids in a protein can offer insights into its three-dimensional structure and its function, cellular location, and evolution. Most of these insights are derived by searching for similarities with other known sequences. Thousands of sequences are known and available in databases accessible through the Internet. A comparison of a newly obtained sequence with this large bank of stored sequences often reveals relationships both surprising and enlightening. Exactly how the amino acid sequence determines three-dimensional structure is not understood in detail, nor can we always predict function from sequence. However, protein families that have some shared structural or functional features can be readily identified on the basis of amino acid sequence similarities. Individual proteins are assigned to families based on the degree of similarity in amino acid sequence. Members of a family are usually identical across 25% or more of their sequences, and proteins in these families generally share at least some structural and functional characteristics. Some families are defined, however, by identities in volving only a few amino acid residues that are critical to a certain function. A number of similar substructures (to be defined in Chapter 4 as “domains”) occur in many functionally unrelated proteins. These domains often fold into structural configurations that have an unusual degree of stability or that are specialized for a certain environment. Evolutionary relationships can also be in ferred from the structural and functional similarities within protein families. Certain amino acid sequences serve as signals that determine the cellular location, chemical modification, and half-life of a protein. Special signal sequences, usually at the amino terminus, are used to target certain proteins for export from the cell; other proteins are targeted for distribution to the nucleus, the cell surface, the cytosol, and other cellular locations. Other sequences act as attachment sites for prosthetic groups, such as sugar groups in glycoproteins and lipids in lipoproteins.

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مواضيع ذات صلة

Overview of Protein Structure:- The Peptide Bond Is Rigid and Planar

Overview of Protein Structure:- A Protein’s Conformation Is Stabilized Largely by Weak Interactions

Protein Sequences and Evolution:- Protein Sequences Can Elucidate the History of Life on Earth

The Covalent Structure of Proteins:- Small Peptides and Proteins Can Be Chemically Synthesized

The Covalent Structure of Proteins:- Amino Acid Sequences Can Also Be Deduced by Other Methods

The Covalent Structure of Proteins:-Large Proteins Must Be Sequenced in Smaller Segments

The Covalent Structure of Proteins:- Short Polypeptides Are Sequenced Using Automated Procedures

The Covalent Structure of Proteins:-The Amino Acid Sequences of Millions of Proteins Have Been Determined

The Covalent Structure of Proteins:-The Function of a Protein Depends on Its Amino Acid Sequence

Working with Proteins:- Unseparated Proteins Can Be Quantified

Working with Proteins:- Proteins Can Be Separated and Characterized by Electrophoresis

Working with Proteins:- Proteins Can Be Separated and Purified