If present, then the cell wall of a prokaryotic cell will contain peptidoglycan, which is carbohydrate polymers cross-linked by proteins. In contrast with eukaryotic cells, if a cell wall is present, it will contain cellulose or chitin. Chitin is a polysaccharide, as is and , both similar in chemical structure to . Like cellulose, chitin contributes strength and protection to the organism. So eukaryotic cells are often stronger than prokaryotic cells.
Eukaryotic cells usually contain mitochondria, which are the site of aerobic respiration, and they absorb glucose and oxygen. They also provide energy, which is transferred in cells. However these aren’t present in prokaryotic cells. Chloroplasts are present in photosynthetic cells. Ribosomes are organelles found in both prokaryotes and eukaryotes. There are two types in eukaryotic cells. One is found in the cytoplasm, which is the region between the nucleus and the cell membrane and the other, smaller type is found in the mitochondria. The prokaryotic cells only contain one type of ribosome of one size.
The size of these two types of cells is different too. Eukaryotic cells have up to one thousand times more volume than a prokaryotic cell.
Many cells have specialized cytoskeletal structures called flagella and cilia. Flagella usually occur one per organism whereas cilia are present as many, many per cell. Flagella are long, hairlike organelles that extend from the cell, permitting it to move. In prokaryotic cells, such as bacteria, the flagella rotate like the propeller of a motorboat. In eukaryotic cells, such as certain protozoa and sperm cells, the flagella whip about and propel the cell. Cilia are shorter and more numerous than flagella. Cilia use a molecule called kinesin, which has an ATPase activity, i.e. it uses the energy in ATP for its 'engine'. This energy is used to let kinesin bind to microtubules, long molecules present in nearly every eukaryotic cell, used for movement. In moving cells, the cilia wave in unison and move the cell forward. Paramecium is a well-known ciliated protozoan. Cilia are also found on the surface of several types of cells, such as those that line the human respiratory tract.
Biochemically both are used for movement and are driven by 'molecular engines'. Binding kinesin to microtubules and the generation of force, results in movement. Flagella are extracellular, attached to the cell at a structure, which contains its 'molecular engine'. This engine is not powered by ATP, but rather by the ‘proton-motive force’ across the plasma membrane. This is the force generated by the difference in proton concentrations on the two sides of the membrane. This results in a pH gradient (more H+ on one side than the other).
Centrioles are found in animal cells and play a role in cell division. Centrioles replicate in the interphase stage of mitosis and they help to organize the assembly of microtubules during cell division. Centrioles called ‘basal bodies’ form cilia and flagella.
A basal body is like a centriole except that it is found at the base of a cilium or flagellum. Both centrioles and basal bodies are similar in that they consist of an outer ring of nine paired tubulin tubes
Cilia and flagella have a similar structure except that in the centre of the ring of tubulin tubes is an additional pair of tubulin tubes. This arrangement is universal among all eukaryotes, such as protists, that have cilia and flagella. Cilia and flagella move in a whip like fashion, which is accomplished using a separate set of proteins that form arms attached to the tubulin. These protein arms allow neighbouring tubulin tubes to slide past each other and bend the cilium.
Since eukaryote flagella and cilia move using kinetic energy generated within the structure some scientists have proposed the term undulapodia for these structures to distinguish them clearly from bacterial flagella.
