The nucleus is the brain of eukaryotic cells. It is only present in eukaryotic cells (which are eukaryotic because they have a nucleus) and there is only one of these organelles in each cell. Usually the nucleus is round and is the largest organelle in the cell. It is surrounded by a membrane, called the nuclear envelope, which is similar to the cell membrane that encloses the entire cell. The envelope is riddled with holes, called nuclear pores, that allow specific materials to pass in and out of the nucleus, just like proteins in the cell membrane regulate the movement of molecules in and out of the cell itself. Attached to the nuclear envelope is the endoplasmic reticulum. The nucleus is surrounded by the cytoplasm inside a cell.
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The nucleus is the pink half-sphere in the center of the cell.
Source: Audesirk, Gerald, and Audesirk, Teresa. Biology: Life on Earth. |
DNA to protein
Source:
http://cellbio.utmb.edu/cellbio/ribosome.htm |
The nucleus houses the DNA (deoxyribonucleic acid) which stores genetic information for a cell. The DNA contains instructions for the production of the cell's proteins and for reproduction. To construct proteins, the DNA is copied to messenger RNA (ribonucleic acid) in the process called transcription. The mRNA goes to the ribosomes, either in the nucleus or in the endoplasmic reticulum, where the actual construction of the proteins takes place.
Structurally, the nucleus is composed of three main parts, the nucleolus, the nuclear envelope, and the chromatin. The nucleolus contains ribosomes, RNA, DNA, and proteins. The nucleolus has some of the ribosomes that synthesize proteins (others are in the endoplasmic reticulum). The chromatin (meaning "colored substance") contains DNA and proteins formed into packets of code called chromosomes. When the cell divides, the chromosomes fold up on themselves, getting wider. The nuclear envelope is important because it allows the nucleus to control the rest of the cell, such as by sending out ATP. The envelope will let molecules like ATP through but will keep other things in or out, so the nucleus is isolated from the cytoplasm.
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