We are learning about proteins and their structure, but one thing is confusing me.
At what structural point is something considered a protein? Is a protein formed after two amino acids synthesis, or is a protein the whole structure (all four levels) put together?
I would think you would need all four structural levels to form a protein, but my teacher refers to the first structure as a protein molecule.
Thanks for the clarification.
They need all three levels of structure (i.e., primary, secondary, and tertiary structure.) Anything less than 20 amino acids is rarely consider a protein, and not all proteins have quanternary structure. Only proteins that are composed of two or more polypeptide chains are considered to have quanternary structure.
Thanks! Great answer. :)
To understand when something is considered a protein, it's important to be familiar with the different levels of protein structure. A protein molecule consists of four levels of structure: primary, secondary, tertiary, and quaternary.
1. Primary structure: This represents the linear sequence of amino acids in a protein. It is formed by the covalent bonds (peptide bonds) that link one amino acid to the next.
2. Secondary structure: This refers to the folding of the polypeptide chain into specific patterns like alpha-helices or beta-sheets. These structures are stabilized by hydrogen bonds between the backbone atoms.
3. Tertiary structure: This describes the 3D shape a protein takes as a result of interactions between amino acid side chains. These interactions include hydrogen bonding, ionic interactions, hydrophobic interactions, and disulfide bonds.
4. Quaternary structure: This level of structure is relevant when multiple protein subunits come together to form a functional protein complex. The subunits are held together by various interactions.
Now, to answer your question, a protein can technically be considered a protein even at the primary structure level. A linear sequence of two or more amino acids linked together by peptide bonds is known as a peptide or a polypeptide. If a polypeptide is relatively short, it may be referred to as a peptide. However, once the polypeptide chain becomes longer and possesses a specific biological function, it can be classified as a protein, even if it lacks higher levels of structure. So, a protein molecule can exist at the primary structure level.
However, it's important to note that proteins usually become fully functional when they fold into their secondary, tertiary, and in some cases, quaternary structures. These higher levels of protein structure are crucial for the protein's stability, function, and the interactions it can have with other molecules. So, while a protein can be considered a protein at the primary structure level, it often requires the full complement of structural levels to exhibit its biological role.