Editing Genetics (section)

=== Genetic code ===
{{Main|Genetic code}}

[[File:Genetic code.svg|class=skin-invert-image|thumb|left|upright=1.3|The [[genetic code]]: Using a [[Genetic code#Discovery|triplet code]], DNA, through a [[messenger RNA]] intermediary, specifies a protein.]]

Genes [[Gene expression|express]] their functional effect through the production of proteins, which are molecules responsible for most functions in the cell. Proteins are made up of one or more polypeptide chains, each composed of a sequence of [[amino acid]]s. The DNA sequence of a gene is used to produce a specific [[Protein primary structure|amino acid sequence]]. This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called [[Transcription (genetics)|transcription]].

This [[messenger RNA]] molecule then serves to produce a corresponding amino acid sequence through a process called [[translation (biology)|translation]]. Each group of three nucleotides in the sequence, called a [[codon]], corresponds either to one of the twenty possible amino acids in a protein or an [[stop codon|instruction to end the amino acid sequence]]; this correspondence is called the [[genetic code]].<ref>{{cite book |title=Biochemistry |vauthors=Berg JM, Tymoczko JL, Stryer L, Clarke ND |edition=5th |year=2002 |publisher=W.H. Freeman and Company |location=New York |chapter-url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=stryer.section.685 |chapter=I. 5. DNA, RNA, and the Flow of Genetic Information: Amino Acids Are Encoded by Groups of Three Bases Starting from a Fixed Point |url-status=live |archive-url=https://web.archive.org/web/20060411095303/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=stryer.section.685 |archive-date=11 April 2006}}</ref> The flow of information is unidirectional: information is transferred from nucleotide sequences into the amino acid sequence of proteins, but it never transfers from protein back into the sequence of DNA—a phenomenon [[Francis Crick]] called the [[central dogma of molecular biology]].<ref name="crick1970">{{cite journal | vauthors = Crick F | title = Central dogma of molecular biology | journal = Nature | volume = 227 | issue = 5258 | pages = 561–563 | date = August 1970 | pmid = 4913914 | doi = 10.1038/227561a0 | url = http://www.nature.com/nature/focus/crick/pdf/crick227.pdf | url-status = live | s2cid = 4164029 | df = dmy-all | bibcode = 1970Natur.227..561C | archive-url = https://web.archive.org/web/20060215024341/http://www.nature.com/nature/focus/crick/pdf/crick227.pdf | archive-date = 15 February 2006 }}</ref>

The specific sequence of amino acids [[protein folding|results]] in a unique three-dimensional structure for that protein, and the three-dimensional structures of proteins are related to their functions.<ref>Alberts et al. (2002), [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.388 I.3. Proteins: The Shape and Structure of Proteins] {{Webarchive|url=https://web.archive.org/web/20230101101721/https://www.ncbi.nlm.nih.gov/books/NBK26830/ |date=1 January 2023 }}</ref><ref>Alberts et al. (2002), [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.452 I.3. Proteins: Protein Function] {{webarchive|url=https://web.archive.org/web/20060425162405/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.452 |date=25 April 2006 }}</ref> Some are simple structural molecules, like the fibers formed by the protein [[collagen]]. Proteins can bind to other proteins and simple molecules, sometimes acting as [[enzyme]]s by facilitating [[chemical reaction]]s within the bound molecules (without changing the structure of the protein itself). Protein structure is dynamic; the protein [[hemoglobin]] bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood.{{cn|date=October 2022}}

A [[Single-nucleotide polymorphism|single nucleotide difference]] within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change the properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, [[sickle-cell anemia]] is a human [[Genetic disorder|genetic disease]] that results from a single base difference within the [[coding region]] for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties.<ref>{{cite web |title=How Does Sickle Cell Cause Disease? |url=http://sickle.bwh.harvard.edu/scd_background.html |date=11 April 2002 |access-date=23 July 2007 |publisher=Brigham and Women's Hospital: Information Center for Sickle Cell and Thalassemic Disorders |url-status=live |archive-url=https://web.archive.org/web/20100923165921/http://sickle.bwh.harvard.edu/scd_background.html |archive-date=23 September 2010}}</ref>
Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort the shape of [[red blood cell]]s carrying the protein. These sickle-shaped cells no longer flow smoothly through [[blood vessel]]s, having a tendency to clog or degrade, causing the medical problems associated with this disease.<ref>{{Cite journal |last1=Elendu |first1=Chukwuka |last2=Amaechi |first2=Dependable C. |last3=Alakwe-Ojimba |first3=Chisom E. |last4=Elendu |first4=Tochi C. |last5=Elendu |first5=Rhoda C. |last6=Ayabazu |first6=Chiagozie P. |last7=Aina |first7=Titilayo O. |last8=Aborisade |first8=Ooreofe |last9=Adenikinju |first9=Joseph S. |date=2023-09-22 |title=Understanding Sickle cell disease: Causes, symptoms, and treatment options |journal=Medicine |language=en |volume=102 |issue=38 |pages=e35237 |doi=10.1097/MD.0000000000035237 |issn=0025-7974 |pmc=10519513 |pmid=37746969}}</ref>

Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called [[non-coding RNA]]. In some cases, these products fold into structures which are involved in critical cell functions (e.g. [[ribosomal RNA]] and [[transfer RNA]]). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as [[microRNA]]).<ref>{{Cite journal |last1=Marques |first1=Tânia Monteiro |last2=Gama-Carvalho |first2=Margarida |date=2022-02-19 |title=Network Approaches to Study Endogenous RNA Competition and Its Impact on Tissue-Specific microRNA Functions |journal=Biomolecules |language=en |volume=12 |issue=2 |pages=332 |doi=10.3390/biom12020332 |doi-access=free |pmid=35204832 |pmc=8868585 |issn=2218-273X }}</ref>