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Subject - Cell Biology

The membrane bound nucleus of a eukaryotic cell contains the genetic material, DNA, in the form of chromosomes. Here, the genetic information in the DNA is translated into the messenger RNA (mRNA), a process also called transcription.

The mRNA is transported to ribosomes in the cytoplasm and translated (translation) into a protein. These spherical organelles are also made of proteins and nucleic acid (RNA).

The eukaryotic cell

The ribosomes may be in contact with the endoplasmic reticulum (ER), a system of tubes that permeates the entire cell. In the ER proteins are chemically modified, e.g. by the addition of sugar units.

The Golgi apparatus is a system of membrane-bound cavities piled on top of each other in flattened stacks called dictyosomes. Proteins are modified here, but they are also sorted, concentrated, stored, and transported.

Lysosomes and spherosomes are membrane-bound particles in the cell plasma that contain various metabolic enzymes.

The cell obtains energy from the mitochondria. "Burning" carbohydrates produces energy in the form of ATP. Mitochondria are surrounded by a double membrane and contain small, individual DNAs in the form of ring-shaped plasmids.

Microtubules, microfilaments, and intermediate filaments are tubular aggregates of proteins. They are important for movement processes within the cell and for the cytoskeleton, which permeates the cell and provides a certain amount of structural stability.

Some eukaryotic cells can move, some can crawl like amoebae, while others have cilia or flagella with which they can move themselves around. Although these flagella have the same name as those of the prokaryotes, they have a completely different composition. Eukaryotic cilia and flagella are made of microtubules.

Plant cells also have special organelles, the membrane-bound chloroplasts, in which photosynthesis occurs.

Prokaryotes have no nucleus and no organelles that are bound by their own membranes. They thus have no mitochondria or lysosomes, for example.

See also: cell , cell membrane , eukaryotes , prokaryotes