Certain pigments found in cells take on different colors depending upon the pH of their environment. For example, betacyanin (responsible for the red color in beets) and a variety of anthocyanins (responsible for the colors in many flowers) appear colored only under acidic conditions. In neutral or basic conditions, they are colorless. These pigments are usually found concentrated within the vacuoles of cells, where they are colored. From this, you can rightly surmise that the interior of a vacuole is acidic. As you think about these pigments, you begin to wonder how it is that they get concentrated within the vacuoles in the first place. Upon doing more research, you find four interesting things that are pertinent to the question at hand:
There appear to be no specific transport systems for these pigments. In other words, there are no systems that will take pigments from the cytosol and move them specifically into the vacuoles.
The interior of the vacuole is kept acidic by a system that constantly moves H+ions into the vacuole. Thus, the pH of the vacuole is determined by a mechanism that does not involve the pigments.
Each of these pigments is uncharged and nonpolar at neutral and basic pH but acts as a base when dissolved in water.
Compounds that are uncharged and nonpolar can freely cross the membrane surrounding the vacuole; compounds that are charged and/or polar cannot.
Given this information, can you figure out how it is that these pigments become concentrated within vacuoles?
According to the research it is found that the pigments are concentrated inside the vacuoles and since the inside of the vacuoles is acidic, the pigments tend to show color inside the vacuoles. The vacuoles are membrane enclosed sac that mostly consists of water. The pigments are nonpolarand uncharged and are also able to dissolve in the water as base. Since pigments being non polar and uncharged, they are freely able to cross the membrane of the vacuole through simple diffusion and hence they enter the vacuoles. Once inside the vacuole, they dissolve in the water and tend to act as base but with the increase influx of the H+, it tends to increase the acidity of the vacuole and hence it helps in formation of the colors in pigments.
Certain pigments found in cells take on different colors depending upon the pH of their environment....
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