Cell (biology)

From ArticleWorld

The cell (biology) is a component of all living organisms and is considered the building block of life. It is the basic structure and functional component of unicellular and multicellular organisms. The theory of the cell was first proposed in 1838 by Schleiden and Schwann. This theory stated that all organisms are made up of cells and all cells are derived from existing cells, all vital functions for life occur in cells and that cell contain all the information that is inherited in the next generation including information on cell functions.

Properties

Every cell is able to maintain itself to some extent by the conversion of nutrients into energy to carry out the required functions and reproduce if necessary. They are self-contained and have their own particular set of instructions. There are some common abilities shared by all cells. These are as follows:

• Reproduction by cellular division.
• Metabolism to obtain energy.
• Response to both internal and external stimuli.
• Movement of vesicles.

There are also common components in all cells. These include:

• A cellular membrane to control the cell's internal environment and regulate what enters and leaves. This layer is also referred to as the phospholipids bilayer due to its composition.
• A cytoskeleton made up of microfilaments which organize the shape, keeps the organelles in their rightful position and aids the cell in mobility.
• The genetic material of a cell is also important and composes of DNA and RNA. DNA is usually the long term storage for information and the RNA is useful for information transport.
• The cell is also composed of what is considered little organs called organelles. These are modified to carry out one or more important functions.

The organelles

One of the more important organelles in a cell is the nucleus. This is found in eukaryotic cells and contains the genetic information. DNA and RNA synthesis both take place in the nucleus. The nucleus is bound by a nuclear envelop that protects its contents from mixing with the rest of the cells components.

Ribosomes are the protein production centers in cells and are found in both eukaryotic and prokaryotic cells. They process the genetic code in mRNA and translate this code into an amino acid sequence.

Mitochondria and chloroplasts are the generators of energy in cells. Mitochondria occur in all types of eukaryotic cells but chloroplasts are only found in photosynthetic eukaryotes like plants.

Other organelles include the endoplasmic reticulum and Golgi apparatus that handle the transport of the macromolecules. The lysosomes and peroxisomes are the disposal systems of cells as they digest the waste components of cells. Centrioles aid in the creation of mitotic apparatus and the vacuoles are the storage organelles for food and water.

Prokaryotes vs. eukaryotes

Prokaryotic cells lack the presence of a nuclear membrane and do not possess most of the organelles found in eukaryotes. They are typically found as unicellular organisms and the functions are carried out by the plasma membrane. One organelle in common between the two cell types is the ribosomes.

Eukaryotic cells are normally found in multi-cellular organisms and tend to be significantly larger than prokaryotes. Eukaryotes have membrane-bound compartments which carry out specific metabolic activities.