What can affect the structure and function of proteins?

Post-translational modifications play a critical role in influencing the structure and function of proteins. After a protein is synthesized, it can undergo various modifications that can significantly alter its activity, stability, localization, and interactions with other molecules. These modifications include phosphorylation, glycosylation, ubiquitination, and acetylation, among others.

For instance, phosphorylation can activate or deactivate certain enzymes, thereby regulating metabolic pathways. Glycosylation, the attachment of carbohydrate moieties, can affect a protein's stability in the bloodstream and its recognition by immune cells. Furthermore, these modifications can facilitate proper folding and help proteins attain their functional conformations, which are essential for their biological roles.

Regarding the other options, while temperature changes and environmental pH levels can indeed influence protein structure (e.g., causing denaturation), they are not the sole factors that affect proteins extensively. Similarly, the speed of protein synthesis can impact the folding process and the emergence of proper structures, but it is the post-translational modifications that directly translate to functional regulation and diversity in the proteome. Therefore, post-translational modifications represent a fundamental mechanism through which proteins can be dynamically regulated after their synthesis.