Eukaryotic Cells - The Nucleus
All eukaryotic cells have at least one nucleus (prokaryotic cells, such as bacteria, lack a nucleus and nuclear membrane). Some cells contain more than one nucleus; osteoclasts (a type of bone cell) usually contain 12 nuclei or more
The NucleusÂ
The nucleus can be thought as the control center for the cell because it contains the instructions to make proteins, and proteins can then make other molecules needed for cellular function and survivalÂ
The nucleus contains DNA, which contains genes. Genes contain the instructions for cellular function and survival. For example, the insulin gene contains instructions to make insulin protein. There are also genes that contain instructions for enzymes that are then used to make other molecules necessary for cellular function. In addition, genes are units of inheritance that pass information from parents to their childrenÂ
The nucleus is also the site for the synthesis of three main types of ribonucleic acid (RNA). These RNA molecules move from the nucleus to the cytoplasm and carry out the synthesis of proteins. These three types of RNA are as follows:Â
Messenger RNA (mRNA), which is made from genetic information transcribed from DNA in a process called transcription, mRNA travels to ribosomes in the cytoplasm so these instructions can be used to make proteinsÂ
Ribosomal RNA (rRNA), is the RNA component of ribosomes, the site of proteins productionÂ
Transfer RNA (tRNA), transports amino acids to ribosomes so that mRNA can be turned into a sequence of amino acids. This process, known as translation, uses the mRNA template to link amino acids to synthesize proteinsÂ
The nucleoplasm inside the nucleus is separated from the cytoplasm outside of the nucleus by the nuclear envelope that surrounds the nucleus. The nuclear envelope contains many nuclear pores. Fluids, electrolytes, RNA, some proteins, and some hormones move in both directions through the nuclear pores, and this exchange between the nucleoplasm and cytoplasm appears to be regulated
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