All known proteins in cells adopt a single stable conformation because
(a) any chain of amino acids can fold up into only one stable conformation.
(b) protein chains that can adopt several different conformations have been weeded out by natural selection.
(c) chaperone proteins prevent the protein from adopting a preferred unstable
conformation.
(d) they are complexed with other molecules that keep them in that one particular
conformation.
(e) one conformation always has the most positive free energy.
-I'm going with (b) with this one because that is the reason why the cell uses only 20 amino acids out of the numberous ones out there.
Well, aren't you quite the "selective" thinker! I'm sorry to burst your bubble, but (b) is not quite the answer we're looking for here. While natural selection does play a role in the evolution of proteins, it doesn't directly determine the ability of proteins to adopt multiple conformations. So, let's keep searching for the right answer, shall we? Clue: think about the nature of protein folding and stability!
Actually, (b) protein chains that can adopt several different conformations have been weeded out by natural selection, is not the correct answer to the question "All known proteins in cells adopt a single stable conformation because...". The correct answer is (a) any chain of amino acids can fold up into only one stable conformation.
The reason for this is mainly determined by the amino acid sequence of the protein. Proteins fold into specific three-dimensional structures based on the sequence of amino acids that make up the protein chain. The sequence information is encoded in the DNA of the organism.
When a protein is synthesized, the linear chain of amino acids undergoes a process called folding, where it spontaneously forms a unique and stable three-dimensional structure. This process is driven by various intermolecular forces such as hydrogen bonding, electrostatic interactions, and hydrophobic interactions.
The specific sequence of amino acids in a protein determines the pattern of these interactions, which in turn determines the final folded structure. The stable conformation of a protein is the one that minimizes the energy of the system and maximizes stability. This is often referred to as the protein's native conformation.
It is important to note that while most proteins adopt a single stable conformation, some proteins called intrinsically disordered proteins (IDPs) or intrinsically disordered regions (IDRs) may not have a well-defined three-dimensional structure. These proteins or regions remain flexible and do not adopt a single stable conformation.
In summary, proteins adopt a single stable conformation because the specific sequence of amino acids determines the folding pattern, and the final protein structure is the one that minimizes the energy and maintains stability.