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Life in all its diversity is composed of only two types of cells: Eukaryotic and Prokaryotic. Prokaryotic cells are simple, one-celled organisms; such as bacteria. All other life is composed of Eukaryotic cells. Not surprisingly, Prokaryotic cells are far simpler in structure and they are also much smaller than Eukaryotic cells. Eukaryotic cells are around 15 times wider and can be up to 1,000 times larger in volume. A hint at one of the critical differences between the two type of cells is in their names; Eukaryotic, derived from the Greek, means “true nucleus, ” whereas Prokaryotic means “before the nucleus.” In addition to having a nucleus, Eukaryotic cells have a nucleolus containing the cell’s DNA, as well as specific membrane-bound compartments, organelles, where specific metabolic activities occur. Prokaryotic cells do not have a nucleus or contain these more complex inner structures. Let’s take a closer look at the components of the Eukaryotic cells.
Nucleolus: A nucleolus is a non membrane bound structure that is made up of nucleic acids and proteins within the nucleus. It is responsible for the manufacture of the subunits that eventually make up ribosomes, which are the cell’s protein producing factories.
Nucleus: The nucleus is the cell’s “control center” and it contains most of the cell’s genetic material. This material makes up DNA molecules and form chromosomes. Inside these chromosomes are the nuclear genomes. It is responsible for maintaining the integrity of the genes and regulating gene expression.
Ribosomes: The ribosomes are actually components of cells that turn amino acids into proteins. In most living things, DNA produces RNA, which then makes protein for the body. Ribosomes are responsible for reading the information from the messenger RNA and using that information to produce the right proteins.
Vesicle: Vesicles are bubbles of liquid inside a cell that stores and transports various substances within that cell. They store both cellular products and waste. They are also responsible for disposing waste. Vesicles are only found in animal cells.
Rough Endoplasmic Reticulum (ER): The surface of an ER is studded with special ribosomes that produce protein. These ribosomes are not stable until they actually bind to the ER. This occurs when the ER begins to synthesize proteins meant for the secretion pathway. The ER is necessary to many functions: secreting proteins, producing important membrane proteins, assembling glycosylation, and producing lysosomal enzymes.
Golgi Apparatus: The primary function of this organelle is to process and then package proteins and lipids after they are synthesized but before they continue on to their destination; it’s almost like the middleman of the equation. This is especially important for the processing of proteins meant for secretion.
Cytoskeleton: This is a kind of skeleton that is made up of protein which is found inside the cytoplasm. Present in all cells, it’s important for the intracellular transport of vesicles and organelles, as well as the process of cellular division.
Smooth Endoplasmic Reticulum: Called the SER, these organelles are important to the metabolic processes like the synthesis of steroids and lipids, the regulation of calcium concentration, the metabolism of carbohydrates, drug detoxification, and more.
Mitochondria: This is a membrane-enclosed organelle that is sometimes called “cellular power plants” because it generates the cell’s supply of ATP, which is its chemical energy source. Mitochondria are also involved in a few minor processes within the cell.
Vacuole: They are compartments filled with water that contains organic and inorganic molecules in solution. They can absorb materials within the cells. Their function varies depending on where they are present but they contain waste products, maintain an acidic internal pH, maintain turgor within cells, and export unwanted materials from the cells. This organelle is present in all plant and fungal cells, as well as some animal cells.
Cytoplasm: This part of the cell is also enclosed in the membrane. It’s where most cellular activities occur including cell division. Many metabolic pathways are constructed there as well.
Lysosome: These are spherical cells that contain enzymes. They break down food to make it easier to digest in the body. They are sometimes referred to as “suicide bags” because they also sometimes digest themselves. Lysosomes are only found in animal cells.
Centrioles within centrosome: These cells are barrel-shaped cells that are not found in plants and most fungi. Only present in animal cells, they are necessary to cell division.
Cell Wall: The cell wall is a flexible but tough layer that surrounds certain types of cells. It offers protection against mechanical stress. In some cases, it allows organism to build and hold a certain shape. The cell wall also limits the amount of large, possibly toxic membranes into cells. It’s only present in plant and fungal cells, not animal cells.
