Vitamin A is needed for the synthesis of important proteins used throughout the body. Vitamin A in the form of retinoic acid can act as a hormone to affect how genes make protein, as shown in Figure 3-5. Retinoic acid is transported to the cells bound to special proteins, cytoplasmic retinoic acid-binding proteins. Once inside the nucleus of the cell, retinoic acid binds to special receptor proteins. Here
Figure 3-5 Vitamin A regulates protein production in the nucleus of the cell.
in the nucleus of the cell, retinoic acid affects gene transcription that enables synthesis of certain proteins. Thyroid hormone and vitamin D interact with retinoic acid in the nucleus of the cell to influence protein synthesis. By regulating which genes are expressed, retinoic acid plays a major role in deciding which type of specialized cell a developing cell will become. This is especially important in embryonic development. This is also important in rapidlydeveloping cells such as epithelial cells in skin and mucous membranes.
This change of a cell to a more specialized cell is called differentiation. Many of the important effects attributed to vitamin Aappear to result from its role in cellular differentiation. Vitamin Ain the form of retinoic acid is essential for fetal development. Retinoic acid is needed for the formation of the heart, eyes, limbs, and ears of the growing fetus. Not only that, but retinoic acid is used to regulate the expression of the gene for growth hormone. Without sufficient retinoic acid, growth hormone may be limited in the developing fetus.
Millions of red blood cells are made in the body every second. Red blood cells are derived from precursor cells called stem cells. These stem cells are dependent on vitamin Afor normal differentiation into red blood cells. In addition, vitamin A facilitates the mobilization of iron from storage areas to the developing red blood cell for integration into hemoglobin. Hemoglobin is the oxygen carrier in red blood cells. Now that we have seen how vitally important vitamin Ais, let us look at the food sources.
Figure 3-5 Vitamin A regulates protein production in the nucleus of the cell.
in the nucleus of the cell, retinoic acid affects gene transcription that enables synthesis of certain proteins. Thyroid hormone and vitamin D interact with retinoic acid in the nucleus of the cell to influence protein synthesis. By regulating which genes are expressed, retinoic acid plays a major role in deciding which type of specialized cell a developing cell will become. This is especially important in embryonic development. This is also important in rapidlydeveloping cells such as epithelial cells in skin and mucous membranes.
This change of a cell to a more specialized cell is called differentiation. Many of the important effects attributed to vitamin Aappear to result from its role in cellular differentiation. Vitamin Ain the form of retinoic acid is essential for fetal development. Retinoic acid is needed for the formation of the heart, eyes, limbs, and ears of the growing fetus. Not only that, but retinoic acid is used to regulate the expression of the gene for growth hormone. Without sufficient retinoic acid, growth hormone may be limited in the developing fetus.
Millions of red blood cells are made in the body every second. Red blood cells are derived from precursor cells called stem cells. These stem cells are dependent on vitamin Afor normal differentiation into red blood cells. In addition, vitamin A facilitates the mobilization of iron from storage areas to the developing red blood cell for integration into hemoglobin. Hemoglobin is the oxygen carrier in red blood cells. Now that we have seen how vitally important vitamin Ais, let us look at the food sources.
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