Question

REFLECT AND APPLY Suggest a reason why the amino acids thyroxine and hydroxyproline are produced by posttranslational modification of the amino acids tyrosine and proline, respectively.

Short answer

Posttranslational modifications allow for specialized functions, such as thyroxine's role in metabolism and hydroxyproline's role in collagen stability.

Step-by-step solution

- Understanding Posttranslational Modification

Posttranslational modification is the process by which proteins undergo further processing after translation. This usually involves the addition of functional groups or the alteration of existing functional groups on amino acids within a protein.

- Identifying the Amino Acids in Question

Thyroxine and hydroxyproline are derived from the amino acids tyrosine and proline, respectively. These derivatives are not directly coded by the genetic material but are formed through modifications after the proteins containing tyrosine and proline are synthesized.

- Purpose of Posttranslational Modifications

Posttranslational modifications can change the chemical properties and functions of proteins. For instance, these changes can impact the protein's stability, activity, and interactions with other molecules.

- Specific Role of Thyroxine

Thyroxine is a hormone produced by the thyroid gland that plays a critical role in regulating metabolism. It is synthesized by iodination of tyrosine residues in the protein thyroglobulin followed by further processing to release active thyroxine.

- Specific Role of Hydroxyproline

Hydroxyproline is a major component of collagen, the primary structural protein in connective tissues. The hydroxylation of proline residues stabilizes collagen’s triple helix structure, providing structural integrity to tissues such as skin, tendons, and bones.

- Reason for Modifications

The posttranslational modifications of tyrosine to thyroxine and proline to hydroxyproline are crucial because they enable these amino acids to serve specialized functions in the body. These modifications enhance the functional diversity of proteins and allow for precise regulatory mechanisms.

Key concepts

Thyroxine

Thyroxine, also known as T4, is a hormone produced by the thyroid gland. It is derived from the amino acid tyrosine through a process called iodination. In this process, iodine atoms are added to the tyrosine residues in the protein thyroglobulin.
Once iodinated, thyroglobulin undergoes further processing, releasing active thyroxine. Thyroxine plays a critical role in regulating metabolism, which includes how the body uses energy. It affects nearly every cell in the body, influencing heart rate, muscle strength, and the speed at which the body uses calories.
People with an imbalance of thyroxine may suffer from conditions like hypothyroidism or hyperthyroidism, highlighting the hormone's importance in maintaining bodily functions.

Hydroxyproline

Hydroxyproline is an amino acid derived from proline via a posttranslational modification known as hydroxylation. This process adds a hydroxyl group (-OH) to proline residues within collagen, the primary protein in connective tissue.
Hydroxyproline is essential for stabilizing collagen's triple helix structure, providing strength and support to tissues like skin, tendons, and bones. This modification is crucial for the structural integrity of these tissues, allowing them to withstand stretching and tearing.
Without sufficient hydroxyproline, collagen would lose its structural stability, leading to weakened connective tissues, which can cause conditions such as scurvy.

Protein Function

Proteins are made up of long chains of amino acids and perform a wide range of functions in the body. Posttranslational modifications (PTMs) are chemical changes that proteins undergo after they are created, which can significantly affect their function.
PTMs can alter the protein's stability, activity, and interactions with other molecules. For example:

• Adding functional groups like phosphate or methyl groups can activate or deactivate proteins.
• Modifying amino acids like tyrosine or proline can create hormones or structural components, such as thyroxine and hydroxyproline.

These modifications are essential for the proteins to carry out specific functions necessary for life. They provide a means for precise regulation and diverse functional capabilities, ensuring proteins meet the body's varying and complex needs.