The cell is the basic structural and functional unit of all known living organisms. They always come from preexisting cells, each cell has the complete genetic information stored in the DNA, and the identical copy of the DNA.
History
Cell theory was first developed in 1839, and states that all organisms are made out of one or more cells. The word “cell” comes from the Latin word “cellula” (a small room).
Type of Cells
There are plant cells and animal cells. The basic difference between a plant cell and an animal cell is that a plant cell has a cell wall and plastids while an animal cell doesn’t.
Parts of a Cell
The most important parts of a cell are the cell membrane, cell wall, cell nucleus, mitochondria and ribosomes. The membrane envelops the cell and makes contact with its environment.
Nutrients enter the cell through the cell membrane through the processes called active and passive diffusion and pinocytosis.
Cell Wall
The cell wall is only present in plant cells, fungi and bacteria. It serves as an additional cell protection. The plant cells’ cell wall is made out of cellulose and bacteria’s cell wall is made of murein.
The Nucleus
The nucleus is the largest cell’s organelle. It is wrapped with two membranes. The outer membrane continues to the endoplasmic reticulum and belongs to the cytoplasm, while the inner membrane belongs to the nucleus and along its walls there is a layer of proteins that helps to maintain the shape of nucleus. The nucleus is called “the control center of the cell”, because it contains the hereditary information.
During cell division, chromosomes are assigned to the daughter cells. The body cells divide in a process called mitosis – resulting 2 daughter cells with 2n number of chromosomes, but the cell division itself makes a short period of cell’s life, and the period between divisions is called interphase (it leads to the DNA duplication).
Mitochondria are round organelles responsible for cellular respiration and generating ATP energy. The main ingredients of mitochondria are lipids, proteins, ribosomes and several circular molecules of DNA and RNA.
Ribosomes are small cytoplasmic structures in which proteins are synthesized. They can be free in the cytoplasm or related to the endoplasmic reticulum, and are built of a large and a small subunit. There are two sizes of ribosomes: size 70 S and 80 S (“S” represents “Svedberg” – a unit of measure of sedimentation rate).
Humans have 100 trillion cells!
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