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Senin, 26 Januari 2009

Journey into the Cell: The Nucleus

The Nucleus:

In Journey into the Cell, we looked at the structure of the two major types of cells: prokaryotic and eukaryotic cells. Now we turn our attention to the "nerve center" of a eukaryotic cell, the nucleus.

The nucleus is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction.
It is commonly the most prominent organelle in the cell.


Nucleus with Nuclear Pores

Liver Cell Nucleus with Dark Nucleolus

Distinguishing Characteristics:
The nucleus is bounded by a double membrane called the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm.

The envelope helps to maintain the shape of the nucleus and assists in regulating the flow of molecules into and out of the nucleus through nuclear pores.

Chromosomes are also located in the nucleus.
When a cell is "resting" i.e. not dividing, the chromosomes are organized into long entangled structures called chromatin and not into individual chromosomes as we typically think of them.

The Nucleolus:
The nucleus also contains the nucleolus which helps to synthesize ribosomes.
The nucleolus contains nucleolar organizers which are parts of chromosomes with the genes for ribosome synthesis on them. Copious amounts of RNA and proteins can be found in the nucleolus as well.

The nucleus controls the synthesis of proteins in the cytoplasm through the use of messenger RNA. Messenger RNA is produced in the nucleolus of the cell and travels to the cytoplasm through the pores of the nuclear envelope.

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