Life sciences · Reference
What is a protein?
A protein is a large molecule built from a chain of amino acids that folds into a specific three-dimensional shape, enabling it to perform a vast range of structural, catalytic, and regulatory roles in living organisms.
From amino acids to proteins
Proteins are polymers of amino acids linked by peptide bonds into chains called polypeptides. The order of amino acids is specified by the sequence of a gene, read out during translation. Once assembled, the chain folds into a particular shape determined largely by its sequence. Because there are 20 amino acids that can be arranged in any order and length, proteins are enormously diverse — the workhorses of the cell.
Levels of protein structure
Protein structure is described at four levels. The primary structure is the linear sequence of amino acids. The secondary structure consists of local folded shapes such as helices and sheets, stabilised by hydrogen bonds.
The tertiary structure is the overall three-dimensional fold of a single chain, and the quaternary structure describes how multiple chains assemble into a larger complex. Correct folding is essential, since a protein’s shape dictates what it can do.
Functions of proteins
Proteins carry out an extraordinary range of tasks. Enzymes catalyse chemical reactions; structural proteins give cells and tissues their shape and strength; transport proteins carry molecules; antibodies recognise foreign material; and signalling and regulatory proteins control cellular processes. This functional versatility is why proteins are central to almost every biological activity.
Proteins in research and standards
Determining protein sequences and structures is a major activity in molecular biology, supported by experimental methods and, increasingly, by computational structure prediction. Databases such as UniProt for sequences and the Protein Data Bank for structures curate this information under shared standards, making protein data findable, interoperable, and reusable across the research community.
Key facts
At a glance
- Definition: a macromolecule of amino acid chains
- Linkage: peptide bonds
- Structure levels: primary, secondary, tertiary, quaternary
- Sequence encoded by: a gene
- Shape determines: function
- Key databases: UniProt (sequences), Protein Data Bank (structures)
Common questions
FAQ
What is a protein made of?+
A protein is made of one or more chains of amino acids joined by peptide bonds. The chain folds into a specific three-dimensional shape that determines the protein’s function.
What do proteins do?+
Proteins perform many roles: enzymes catalyse reactions, structural proteins provide support, transport proteins move molecules, antibodies recognise foreign material, and regulatory proteins control cellular processes.
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