Cell structure

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Most human cells contain small structures known as organelles ("little organs"), each of which performs a highly specialized task, such as manufacturing protein. Organelles are usually surrounded by a membrane, and they float in a jelly-like substance called cytoplasm. Ninety per cent of cytoplasm is water; it also contains enzymes, amino acids, and other molecules needed for cell functions.

Nucleus - the cell's control center mainly contains chromatin, a granular material composed of DNA, the cell's genetic material, and proteins. The inner nucleolus is made up of RNA and proteins. The nucleus is surrounded by the nuclear envelope, a two-layered membrane with pores.

Centrioles - these two structures made of hollow tubules play a key role in cell division

Mitochondrion - this structure produces a substance called adenosine triphosphate (ATP), which is the carrier of energy in all cells

Endoplasmic reticulum - this organelle helps to transport material


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