Nucleus
- The nucleus is the main center of the eukaryotic cell
- It is generally the most obvious cell and has most of the genes in a eukaryotic cell.
- The nuclear envelope encloses the nucleus and helps it separate it from the cytoplasm.. It has a double membrane, and each has a lipid bilayer with associated proteins. The nuclear envelope are perforated (pierced) by pore structures.
- At the end of each pore, an intricate protein structure called a pore complex lines each pore structure and regulates the entry and exit of proteins and RNA.
- Within the nucleus, the DNA is organized into chromosomes, which are structures that contain the genetic information.
- The complex of DNA and proteins making chromosomes is called chromatin.
- An important structure within the nucleus is the nucleolus. Here ribosomal RNA or rRNA ( a type of RNA) is made form instruction from the DNA..
- In the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into large or small subunits of ribosomes. Then the ribosomes exit the nucleus through the pores and into the cytoplasm, where the subunits can combine into a ribosome.
- The nucleus directs protein synthesis by manufacturing messenger RNA( or mRNA) according to instruction from DNA. The mRNA is then transported to the cytoplasm through the pores. Once the mRNA reaches the cytoplasm, ribosomes translate the genetic message of the mRNA into the primary structure of a polypeptide.