A nucleus is a membrane-bound organelle that contains the cell's chromosomes. Pores in the nuclear membrane allow for the passage of molecules in and out of the nucleus.
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The nucleus is one of the most obvious parts of the cell when you look at a picture of the cell. It's in the middle of the cell, and the nucleus contains all of the cell's chromosomes, which encode the genetic material. So this is really an important part of the cell to protect. The nucleus has a membrane around it that keeps all the chromosomes inside and makes the distinction between the chromosomes being inside the nucleus and the other organelles and components of the cell staying outside. Sometimes things like RNA need to traffic between the nucleus and the cytoplasm, and so there are pores in this nuclear membrane that allow molecules to go in and out of the nucleus. It used to be thought that the nuclear membrane only allowed molecules to go out, but now it's realized that there is an active process also for bringing molecules into the nucleus.
Julie A. Segre, Ph.D.
Senior Investigator, Genetics and Molecular Biology Branch; Head, Epithelial Biology Section
Dr. Segre's research focuses on the dynamic process by which the epidermis maintains a proper balance between proliferation and differentiation. Combining classical genetics techniques and modern genomic tools, her laboratory uses mouse models to investigate the function of novel genes important for in utero human epidermal development, normal wound healing and skin regeneration. The epidermis acts as a barrier to infectious agents and protects against the loss of critical bodily fluids. However, in infants born prematurely, immaturity of the skin places them at great risk of disease and early death.