Articles :: Our Body :: Cell Structure

What does a human cell look like? There are three main parts in a human cell. They are plasma membrane, cytoplasm and nucleus. So look 'into' it now!

	Cell Diagram
	Created by Ourselves

Plasma Membrane

The outermost layer is the plasma membrane. It encloses all the contents of a cell. It is a thin membrane, 8- 10 nm, which is made up of lipids and proteins. It is a very special membrane. It is selectively permeable that allows only small particles to pass through but not large ones. Due to concentration gradient, small particles will diffuse into and out of the cell. Diffusion is a passive process, however the cell also has the power to control the movement of materials actively. This is done by carrier proteins in the membrane. In these ways the cell is able to control the concentration of substances and the movement of materials into and out of the cell.

Cytoplasm

Inside the membrane is the cytoplasm which is the whole volume of the cell including the organelles (cell organ) but except nucleus. The cytoplasm is a gelatinous mixture of chemical substance with water and proteins. It is a place for cellular chemical reactions to take place. Oh! What are organelles then? They are small structures that have particular functions. Examples are like nucleus and mitochondrion. I haven't mention about mitochondrion before so let me talk a little bit about it now. Mitochondrion is sausage or rod-shaped. It is a site of aerobic respiration and it contains enzymes that help to release energy during respiration. It is an energy factory. The metabolic level of mitochondrion is high and it is most numerous in a cell.

Nucleus Now this is the most important part! The last main part of a human cell is the nucleus. It is bounded by the nuclear envelope which is a double membrane. Surrounded by the nuclear envelope is the nucleoplasm. Within the nucleoplasm are the chromatins. Chromatins consist of proteins and DNA which carries genetic information and controls all cellular activities.

Cell     Image Courtesy of Pathology Department, PYNEH, Hong Kong

The next topic is about chromosomes. I think you are able to guess that chromosomes are related with chromatins. But again what are chromosomes? Let us continue to find out the mystery of DNA!

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