Difference Between Pili and Fimbriae Pili and fimbriae are the terms that used to describe a short, hair-like projections on the surface of prokaryotic cells like bacterial cells, etc. Pili and fimbriae are the projections other than flagella of the cell, and they are used by the cell for anchoring itself with the surface or for attachment. These Pili and fimbriae are present at the cell surface. The key difference between pili and fimbriae is that pili are found in gram-negative bacteria, whereas fimbriae are found in Gram-negative as well as in gram- positive bacteria. The other prominent differences between pili and fimbriae are of size, length. Pili Fimbriae Fimbriae are found both in gram negative and gram Found in Pili are present in gram-negative bacteria. positive bacteria. Fimbriae are smaller in size and thinner in Size Pili are larger in size and thicker in diameter. diameter. Pili are very rigid structure, and plasmid genes Fimbriae are less rigid structure and are governed Structure govern them. by genes of bacteria in the nucleus. Receptors Pili have receptors for many viruses. Fimbriae have no receptors on them. Pili are composed of a special protein known as Protein Fimbriae have fibrillin protein in their structure. pilin, due to which name pili is used. What is Pili? Pili are the projections or appendages present on the cell surface of the cell. They are present in gram-negative bacteria. Pili are long, thick and tubular structure. They are composed of a special protein known as pilin, due to which they are named Pili. Pili are very rigid structure, and plasmid genes govern them. Pili are mainly used for the attachment of the cell with the other surface but indirectly, they are also used in sexual reproduction by the cell. Hence, they are also used in the reproduction of cell; such pili are known as sex pili. Sex pili are useful in sharing genes between the two cells. Pili also have receptors for many viruses. Pili are abundantly found in the cell as compared to other structure. Note that they do not have any function in locomotion of cell. They are present in Neisseria gonorrhoeae, where they are used for attachment in urogenital and cervical epithelium in disease. What is Fimbriae? Fimbriae are the projections found in gram negative and gram positive bacteria. They are shorter structure, and they have a thin diameter. Fimbriae are so named because they have fibrillin protein in their structure. Fimbriae are less rigid structure and are governed by genes of bacteria in the nucleus. Fimbriae are specialized structures that have the only function of attachment. They do not have any function in locomotion of cell. They have no receptors on them, and they form clusters of cells while sticking with other surface or with each other. An example of fimbriae is Shigella dysenteriae, where it is used to attach on the surface of the intestine to produce toxic substances that mostly cause diarrhea. Pili vs. Fimbriae Pili are present in gram-negative bacteria, whereas fimbriae are found both in gram negative and gram positive bacteria. Pili are larger in size and thicker in diameter, while fimbriae are smaller in size and thinner in diameter. Pili are very rigid structure, and plasmid genes govern them, on the other hand, fimbriae are less rigid structure and are governed by genes of bacteria in the nucleus. Pili have receptors for many viruses, whereas fimbriae have no receptors on them. Pili are composed of a special protein known as pilin, due to which name pili is used and contrary to that, fimbriae have fibrillin protein in their Difference Between Prokaryotic and Eukaryotic Flagella Prokaryotic vs Eukaryotic Flagella Certain eukaryotic and prokaryotic cells have long wipe like appendages or projections called flagella. This structure is vital in locomotion of both eukaryotic and prokaryotic cells. Though the function is the same, there are some differences between eukaryotic and prokaryotic flagella. They mainly differ in the ways of protein composition, structure, and operation mechanism. Prokaryotic Flagella Prokaryotic flagella are structurally very simple and are made up of a single fiber of the flagellin protein, which has 53KDa subunit. The motion of Prokaryotic flagella is whirling like or spinning like. Bacterial flagella are normally visible only under the electron microscope and are located in entirely outside of the plasma membrane. Eukaryotic Flagella The structure of eukaryotic flagellum is complex, and it has 9+2 microtubule structure. The flagellum of eukaryotes is usually surrounded by cell membrane and composed of tubulin. The motion of eukaryotic flagella is a wipe like or “S” shaped. Cilium is another appendage that is similar to flagella which is found in eukaryotic cells. Usually eukaryotic cell has about one or two flagella. Sperm cell is an example for flagellated eukaryotic cell, and moves by means of single flagellum. Eukaryotic flagella are vigorous in movements involving feeding and sensation. What is the difference between Prokaryotic and Eukaryotic Flagella? • Prokaryotic flagella are smaller and simple in structure, whereas eukaryotic flagella are larger and complex in structure. • Prokaryotic flagella are made up of flagellin protein while eukaryotic flagella are made up of tubulin. • The movement of prokaryotic flagella is proton driven, whereas the movement of eukaryotic flagella is ATP driven. • Prokaryotic flagella have rotator movement, whereas eukaryotic flagella have blending movement. • Unlike the prokaryotic flagella, eukaryotic flagella have 9+2 arrangement of microtubules. • Prokaryotic flagella are located outside of the plasma membrane, whereas the flagella in eukaryotes are covered with the plasma membrane. .