Know the different types of surface appendages on prokaryotic cells – Distinguish pili (fimbriae) and flagella
The Correct Answer and Explanation is:
Prokaryotic cells possess various surface appendages that contribute to their functionality. These appendages include pili (also called fimbriae) and flagella, which play distinct roles in the cell’s movement, attachment, and interaction with the environment.
Pili (Fimbriae):
Pili are short, hair-like structures on the surface of prokaryotic cells. They are primarily composed of a protein called pilin. The primary function of pili is to assist in adhesion to surfaces, which is important for colonization, biofilm formation, and infection in host organisms. Some pili, known as sex pili, are involved in conjugation, a process where genetic material is exchanged between bacteria. Fimbriae are generally shorter and more numerous than flagella, often covering the entire surface of the cell.
Flagella:
Flagella are long, whip-like appendages that extend from the surface of many prokaryotic cells. They are mainly responsible for cell motility, enabling bacteria to move toward or away from environmental stimuli, a process known as taxis. The flagellum consists of three parts: the filament (a long helical structure made of flagellin protein), the hook (a flexible region that connects the filament to the motor), and the basal body (which anchors the flagellum to the cell membrane and enables its rotation). Flagella function by rotating in a way that propels the cell forward or backward.
Distinguishing Pili and Flagella:
Although both pili and flagella are surface appendages, they differ in structure and function. Pili are smaller, hair-like projections used primarily for adhesion and genetic exchange, while flagella are larger, tail-like structures used for motility. Pili tend to be more numerous on the cell surface and are involved in surface attachment, whereas flagella are less abundant but much longer and specialized for movement in liquid environments. Additionally, flagella rotate to propel the cell, while pili do not provide motility but rather help in adherence and transfer of genetic material.
