Final answer:
The assertion is false; the three-dimensional structure of proteins can be determined with modern techniques that may not require protein isolation in pure form. Tertiary structure is key to protein function and evolutionary conservation of protein folding is significant. Amino acids from protein degradation can be recycled for new protein synthesis.
Step-by-step explanation:
The statement that 'The three-dimensional structure of a protein cannot be determined unless the protein can be isolated from cells in pure form' is indeed false. The three-dimensional structure of proteins is crucial as it directly relates to their function. With advances in structural biology, we can determine the structure of proteins using techniques like X-ray crystallography, NMR spectroscopy, and cryo-electron microscopy, which do not always require the protein to be isolated in pure form. It's also important to note that proteins can be studied within cells using methods such as in-cell NMR.
When understanding proteins, it's essential to be aware that the tertiary structure refers to the unique three-dimensional shape, including folding and bending driven by interactions among side chains. This structure is central to the protein's functionality, and a figure representing insulin's structure can demonstrate this aspect. Moreover, the conservation of protein folding patterns over evolutionary time often carries more information about relationships between species than comparing DNA sequences, as highly divergent sequences can still fold into similar three-dimensional shapes.
Amino acids being "recycled" refers to the process of proteins getting broken down into their constituent amino acids, which can then be reused by the cell to build new proteins. This recycling is a part of the protein metabolism within the cell, conserving resources and maintaining cellular efficiency.