Editing Cell biology (section)

== Cell types ==
{{Main|Cell types}}
[[File:Prokaryote cell.svg|thumb|A drawing of a prokaryotic cell]]
There are two fundamental classifications of cells: [[Prokaryote|prokaryotic]] and [[Eukaryote|eukaryotic]]. Prokaryotic cells are distinguished from eukaryotic cells by the absence of a [[cell nucleus]] or other membrane-bound [[organelle]].<ref>{{cite book|title=Biochemical Engineering|last1=Doble|first1=Mukesh|last2=Gummadi|first2=Sathyanarayana N.|date=August 5, 2010|publisher=Prentice-Hall of India Pvt.Ltd|isbn=978-8120330528|location=New Delhi}}</ref> Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life.<ref>{{cite book|title=Cell Physiology Sourcebook: A Molecular Approach|last1=Kaneshiro|first1=Edna|date=May 2, 2001|publisher=Academic Press|isbn=978-0123877383|edition=3rd}}</ref> Prokaryotic cells include [[Bacteria]] and [[Archaea]], and lack an enclosed cell nucleus.  Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10 to 100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells. The four eukaryotic kingdoms are '''Animalia, Plantae, Fungi, and Protista.'''<ref>{{Cite book |last1=Levetin |first1=Estelle |url=https://books.google.com/books?id=GaRvEAAAQBAJ |title=Ebook: Plants and Society |last2=McMahon |first2=Karen |date=2014-10-16 |publisher=McGraw Hill |isbn=978-0-07-717206-0 |pages=135 |language=en}}</ref>

They both reproduce through [[binary fission]]. Bacteria, the most prominent type, have several [[Bacterial cell structure#Cell morphology|different shapes]], although most are [[cocci|spherical]] or [[Bacillus (shape)|rod-shaped]]. Bacteria can be classed as either [[Gram-positive bacteria|gram-positive]] or [[Gram-negative bacteria|gram-negative]] depending on the [[Cell wall#Bacterial cell wall|cell wall]] composition. Gram-positive bacteria have a thicker [[peptidoglycan layer]] than gram-negative bacteria. Bacterial structural features include a [[flagellum]] that helps the cell to move,<ref name=":02">{{Cite journal|last=Nelson|first=Daniel|date=2018-06-22|title=The Difference Between Eukaryotic And Prokaryotic Cells|journal=Science Trends|doi=10.31988/scitrends.20655|s2cid=91382191}}</ref> [[ribosome]]s for the translation of RNA to protein,<ref name=":02" /> and a [[nucleoid]] that holds all the genetic material in a circular structure.<ref name=":02" /> There are many processes that occur in prokaryotic cells that allow them to survive. In prokaryotes, '''mRNA synthesis''' is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and a σ protein that assists only with initiation. For instance, in a process termed [[Conjugation pilus|conjugation]], the fertility factor allows the bacteria to possess a pilus which allows it to transmit DNA to another bacteria which lacks the F factor, permitting the transmittance of resistance allowing it to survive in certain environments.<ref>{{Cite journal|last1=Griffiths|first1=Anthony J.F.|last2=Miller|first2=Jeffrey H.|last3=Suzuki|first3=David T.|last4=Lewontin|first4=Richard C.|last5=Gelbart|first5=William M.|date=2000|title=Bacterial conjugation|url=https://www.ncbi.nlm.nih.gov/books/NBK21942/|journal=An Introduction to Genetic Analysis. 7th Edition}}</ref>