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# C. Nucleus The most visible part of a eukaryotic cell is the nucleus. In an animal cell, it is roughly spherical in shape and is generally located at the center of the cell. It is the site where nucleic acids are synthesized. The nucleus also serves as the site for the storage of hereditary facto...

# C. Nucleus The most visible part of a eukaryotic cell is the nucleus. In an animal cell, it is roughly spherical in shape and is generally located at the center of the cell. It is the site where nucleic acids are synthesized. The nucleus also serves as the site for the storage of hereditary factors. It is the source of ribonucleic acid (RNA), a molecule responsible for converting genetic instructions in DNA into functional substances such as proteins. Some cells, however, such as red blood cells and platelets, lose their nucleus as they mature. ## The Structure of the Nucleus * **Nuclear membrane:** This membrane is composed of two layers which separate the nucleus from the cytoplasm and is continuous with the endoplasmic reticulum. It contains ribosomes on its outer membrane. * **Nucleoplasm:** The dense, protein-rich substance inside the nucleus is the nucleoplasm. This is where the spherical, unbound nucleolus is suspended. The nucleolus is rich in proteins and nucleic acids and is where rRNA is transcribed and assembled. * **Nuclear pores:** These are openings in the nuclear membrane. They act as selective channels between the cytoplasm and the inside of the nucleus, selectively allowing molecules that come in and out of the nucleus. The proteins that make up the nuclear pore complex are arranged radially with a large central hole. * **Chromatin:** This is found inside the nucleus and is made up of DNA and proteins. During cell division, the chromatin forms chromosomes. Chromosomes contain the genes inherited by the offspring from their parents. # Figure 1.20. The Nucleus This is an image of what the nucleus looks like. The image is labelled to show: * Nucleolus * Nuclear Envelope * Nuclear Pores * Chromosomes * Chromatin