Ethan Blackwood, Anna Menkis, Jeremy Cohen Elenbaas Block 3 Cilia and Flagella Ethan Blackwood, Anna Menkis, Jeremy Cohen Elenbaas Block 3

Cilia and Flagella: The Basics Thin tubular structures protruding from membranes of some eukaryotic cells Aid in movement Structurally and functionally identical Cilia short in size usually found in great quantities, covering entire cell membrane Flagella (eukaryotic) much longer usually one or two in a cell

General Structure Membrane: extensions of cell membrane Composed of microtubles, organized as following: Central axoneme with 2 microtubles Surrounded by 9 microtuble doublets Axoneme and doublets connected by radial spokes Dynein molecules bridge gaps between doublets Figure 1: Interior structure of cilia and flagella (Credit: Florida State University) Basal body (Kinetosome) located at base 9 sets of 3 microtubules in radial pattern

Microtubules Extensions of internal cytoskeleton Composed of the globular protein tubulin Doublet: one full microtubule sharing a wall with a smaller, partial microtubule Basal body: structurally identical to centriole (part of cytoskeleton of an animal cell)

Process of Movement Protein dynein is activated by ATP Dynein arms on one microtubule doublet “grab” an adjacent doublet and “walk” along its length. Doublets slide past each other and bend Cilium/flagellum bends Figure 2: Movement of cilia and flagella (Credit: Benjamin/Cummings)

General Functions In protista: movement of organism through environment Same function applies to motile (flagellated) sperm cells In multicellular eukaryota: transport extracellular substances (e.g. water, food)

Where Found Cilia Protista (e.g. paramecium) Human respiratory tract, keeping dust and debris out of lungs Digestive systems (e.g. of snails) Flagella (eukaryotic) Protista (e.g. euglena) Motile (flagellated) sperm cells of animals and some plants (Bacterial and archaeal flagella exist in some prokaryotes)

Ciliopathy Problems Primary ciliary dyskinesia Recessive genetic disorder Defective cilia lining respiratory tract and fallopian tube Susceptibility to chronic, recurring respiratory infections Polycystic kidney disease Defective cilia in the renal tube cells (kidney) Cysts, enlargement of kidneys, possible damage to other organs Bardet-Biedl syndrome Problem in basal body caused by genetically mutated cilia Numerous consequences, ranging from obesity to mental retardation Ectopic pregnancy Fallopian cilia fail to move fertilized ovum to uterus

Two Theories of Evolution Endosymbiotic model Proposed by Lynn Margulis Cilia and flagella are results of symbiosis between ancient eukaryotic and prokaryotic cells Supporting evidence (weaker) Mitochondria and chloroplasts as endosymbiotic examples Some eukaryotes symbiotically use bacteria as motility organelles Endogenous model Cilia and flagella developed from existing eukaryotic cytoskeleton Supporting evidence (stronger) Both cilia/flagella and cytoskeleton contain dynein and tubulin All eukaryotic kingdoms contain motile, 9+2 flagella, suggesting that the common eukaryotic ancestor had this trait

Works Cited Campbell, Neil A. et al. Biology: Concepts & Connections. San Francisco: Benjamin/Cummings, 2000. “Cilium-related disease.” Cilium. New World Encyclopedia. newworldencyclopedia.org/entry/Cilia Davidson, Michael W. “Cilia and Flagella.” 2004. Molecular Expressions: Exploring the World of Optics and Microscopy. micro.magnet.fsu.edu/cells/ciliaandflagella/ciliaandflagella.html “How important is endosymbiosis?” Understanding Evolution. University of California Museum of Paleontology and National Center for Science Education. evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_06 Kaiser, Gary E. “Composition and Functions of Eukaryotic Cellular Structures: Cilia and Flagella.” The Eukaryotic Cell. Community College of Baltimore County. student.ccbcmd.edu/courses/bio141/lecguide/unit3/eustruct/ciliaflag.html (For further reading) Mitchell, David R. The Evolution of Eukaryotic Cilia and Flagella as Motile and Sensory Organelles. 2006. SUNY Upstate Medical University. upstate.edu/cdb/mitcheld/publications/Jekey_Mitchell.pdf