Editing Cell biology (section)

==Structure and function==
=== Structure of eukaryotic cells ===
{{Main|Eukaryote}}
[[File:Animal cell NIH.jpg|thumb|A diagram of an animal cell]]
[[Eukaryotic cell#Cell features|Eukaryotic cells]] are composed of the following organelles:
* [[Cell nucleus|Nucleus]]: The nucleus of the cell functions as the [[genome]] and genetic information storage for the cell, containing all the [[DNA]] organized in the form of [[chromosome]]s. It is surrounded by a [[nuclear envelope]], which includes nuclear pores allowing for the transportation of proteins between the inside and outside of the nucleus.<ref name="pmid29107331">{{cite journal | vauthors = Elosegui-Artola A, Andreu I, Beedle AE, Lezamiz A, Uroz M, Kosmalska AJ, Oria R, Kechagia JZ, Rico-Lastres P, Le Roux AL, Shanahan CM, Trepat X, Navajas D, Garcia-Manyes S, Roca-Cusachs P |display-authors = 6| title = Force Triggers YAP Nuclear Entry by Regulating Transport across Nuclear Pores | journal = Cell | volume = 171 | issue = 6 | pages = 1397–1410.e14 | date = November 2017 | pmid = 29107331 | doi = 10.1016/j.cell.2017.10.008 | doi-access = free }}</ref> This is also the site for replication of DNA as well as transcription of DNA to RNA. Afterwards, the RNA is modified and transported out to the cytosol to be translated to protein.<ref>{{Cite web|title=Nucleus|url=https://www.genome.gov/genetics-glossary/Nucleus|access-date=2021-09-27|website=Genome.gov|language=en}}</ref>
* [[Nucleolus]]: This structure is within the nucleus, usually dense and spherical. It is the site of ribosomal RNA (rRNA) synthesis, which is needed for ribosomal assembly.
* [[Endoplasmic Reticulum|Endoplasmic reticulum (ER)]]: This functions to synthesize, store, and secrete proteins to the Golgi apparatus.<ref>{{Cite web|url=https://bscb.org/learning-resources/softcell-e-learning/endoplasmic-reticulum-rough-and-smooth/|title=Endoplasmic Reticulum (Rough and Smooth) {{!}} British Society for Cell Biology|access-date=2019-10-06}}</ref> Structurally, the endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus. The membranes are slightly different from cell to cell and a cell's function determines the size and structure of the ER.<ref>{{Cite web|last=Studios|first=Andrew Rader|title=Biology4Kids.com: Cell Structure: Endoplasmic Reticulum|url=http://www.biology4kids.com/files/cell_er.html|access-date=2021-09-27|website=www.biology4kids.com|language=en}}</ref>
* [[Mitochondria]]: Commonly known as the powerhouse of the cell is a double membrane bound cell organelle.<ref>{{Cite web|title=Powerhouse of the cell has self-preservation mechanism|url=https://www.eurekalert.org/news-releases/801244|access-date=2021-09-27|website=EurekAlert!|language=en}}</ref> This functions for the production of energy or ATP within the cell. Specifically, this is the place where the Krebs cycle or [[Citric acid cycle|TCA cycle]] for the production of NADH and FADH occurs. Afterwards, these products are used within the electron transport chain (ETC) and oxidative phosphorylation for the final production of ATP.<ref>{{Citation|last=Pelley|first=John W.|chapter=Citric Acid Cycle, Electron Transport Chain, and Oxidative Phosphorylation|date=2007|pages=55–63|publisher=Elsevier|isbn=9780323034104|doi=10.1016/b978-0-323-03410-4.50013-4|title=Elsevier's Integrated Biochemistry}}</ref>
* [[Golgi apparatus]]: This functions to further process, package, and secrete the proteins to their destination. The proteins contain a signal sequence that allows the Golgi apparatus to recognize and direct it to the correct place. Golgi apparatus also produce [[glycoprotein]]s and [[glycolipid]]s.<ref>{{Cite journal|last=Cooper|first=Geoffrey M.|date=2000|title=The Golgi Apparatus|url=https://www.ncbi.nlm.nih.gov/books/NBK9838/|journal=The Cell: A Molecular Approach. 2nd Edition}}</ref>
* [[Lysosome]]: The lysosome functions to degrade material brought in from the outside of the cell or old organelles. This contains many acid hydrolases, proteases, nucleases, and lipases, which break down the various molecules. [[Autophagy]] is the process of degradation through lysosomes which occurs when a vesicle buds off from the ER and engulfs the material, then, attaches and fuses with the lysosome to allow the material to be degraded.<ref>{{Cite book|title=Lysosomes: some pathologic implications.|last=Verity, M A|oclc=679070471}}</ref>
* [[Ribosome]]s: Functions to translate RNA to protein. it serves as a site of protein synthesis.<ref>{{Cite web|title=Ribosome {{!}} cytology|url=https://www.britannica.com/science/ribosome|access-date=2021-09-27|website=Encyclopedia Britannica|language=en}}</ref>
* [[Cytoskeleton]]: Cytoskeleton is a structure that helps to maintain the shape and general organization of the cytoplasm. It anchors organelles within the cells and makes up the structure and stability of the cell. The cytoskeleton is composed of three principal types of protein filaments: actin filaments, intermediate filaments, and microtubules, which are held together and linked to subcellular organelles and the plasma membrane by a variety of accessory proteins.<ref>{{Cite book|title=The Cell: A Molecular Approach|publisher=ASM Press|first =Geoffrey M|last = Cooper|year=2000|isbn = 9780878931064}}</ref>
* [[Cell membrane]]: The cell membrane can be described as a phospholipid bilayer and is also consisted of lipids and proteins.<ref name=":02" /> Because the inside of the bilayer is hydrophobic and in order for molecules to participate in reactions within the cell, they need to be able to cross this membrane layer to get into the cell via [[osmotic pressure]], [[diffusion]], concentration gradients, and membrane channels.<ref>{{Cite journal|last=Cooper|first=Geoffrey M.|date=2000|title=Transport of Small Molecules|url=https://www.ncbi.nlm.nih.gov/books/NBK9847/|journal=The Cell: A Molecular Approach. 2nd Edition}}</ref>
* [[Centriole]]s: Function to produce spindle fibers which are used to separate chromosomes during cell division.

Eukaryotic cells may also be composed of the following molecular components:
* [[Chromatin]]: This makes up [[chromosome]]s and is a mixture of DNA with various proteins.
* [[Cilium|Cilia]]: They help to propel substances and can also be used for sensory purposes.<ref>{{Cite web|title=What Are the Main Functions of Cilia & Flagella?|url=https://sciencing.com/main-functions-cilia-flagella-10572.html|access-date=2020-11-23|website=Sciencing|date=10 September 2018 |language=en}}</ref>

=== Cell metabolism ===
Cell metabolism is necessary for the production of energy for the cell and therefore its survival and includes many pathways and also sustaining the main cell organelles such as the nucleus, the mitochondria, the cell membrane etc. For [[cellular respiration]], once glucose is available, glycolysis occurs within the cytosol of the cell to produce pyruvate. Pyruvate undergoes decarboxylation using the multi-enzyme complex to form acetyl coA which can readily be used in the [[Citric acid cycle|TCA cycle]] to produce NADH and FADH<sub>2</sub>. These products are involved in the [[electron transport chain]] to ultimately form a proton gradient across the inner mitochondrial membrane. This gradient can then drive the production of ATP and {{H2O-nl}} during [[oxidative phosphorylation]].<ref name=":0">{{Citation|last1=Ahmad|first1=Maria|title=Biochemistry, Electron Transport Chain|date=2019|url=http://www.ncbi.nlm.nih.gov/books/NBK526105/|work=StatPearls|publisher=StatPearls Publishing|pmid=30252361|access-date=2019-10-20|last2=Kahwaji|first2=Chadi I.}}</ref> Metabolism in plant cells includes [[photosynthesis]] which is simply the exact opposite of respiration as it ultimately produces molecules of glucose.

=== Cell signaling ===
{{Further|Cell signaling}}
[[Cell signaling]] or cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Signaling can occur through direct cell contact or [[Endocrine system|endocrine]], [[Paracrine signaling|paracrine]], and [[autocrine signaling]]. Direct cell-cell contact is when a receptor on a cell binds a molecule that is attached to the membrane of another cell. Endocrine signaling occurs through molecules secreted into the bloodstream. Paracrine signaling uses molecules diffusing between two cells to communicate. Autocrine is a cell sending a signal to itself by secreting a molecule that binds to a receptor on its surface. Forms of communication can be through:
* [[Ion channel]]s: Can be of different types such as voltage or ligand gated ion channels. They allow for the outflow and inflow of molecules and ions.
* [[G protein-coupled receptor|G-protein coupled receptor]] (GPCR): Is widely recognized to contain seven transmembrane domains. The ligand binds on the extracellular domain and once the ligand binds, this signals a guanine exchange factor to convert GDP to GTP and activate the G-α subunit. G-α can target other proteins such as adenyl cyclase or phospholipase C, which ultimately produce secondary messengers such as cAMP, Ip3, DAG, and calcium. These secondary messengers function to amplify signals and can target ion channels or other enzymes. One example for amplification of a signal is cAMP binding to and activating PKA by removing the regulatory subunits and releasing the catalytic subunit. The catalytic subunit has a nuclear localization sequence which prompts it to go into the nucleus and phosphorylate other proteins to either repress or activate gene activity.<ref name=":0" />
* [[Receptor tyrosine kinase]]s: Bind growth factors, further promoting the tyrosine on the intracellular portion of the protein to cross phosphorylate. The phosphorylated tyrosine becomes a landing pad for proteins containing an SH2 domain allowing for the activation of Ras and the involvement of the [[Mitogen-activated protein kinase|MAP kinase pathway]].<ref>{{Cite journal|last=Schlessinger|first=Joseph|date=October 2000|title=Cell Signaling by Receptor Tyrosine Kinases|journal=Cell|volume=103|issue=2|pages=211–225|doi=10.1016/s0092-8674(00)00114-8|pmid=11057895|s2cid=11465988|issn=0092-8674|doi-access=free}}</ref>