 In this tutorial we will learn how to search for rear reactions with the gene ontology. The gene ontology, or GO, consists of a set of terms and concepts with relations that operate between them. GO attempts to describe our knowledge of the biological domain with respect to three aspects. Biological process, molecular function and cellular component. Rear reactions are mapped through terms from the GO category Molecular Function. The mapping is maintained by the GO consortium. About one third of the rear reactions are currently mapped to GO. Making the links is an ongoing process. Let's start by looking how GO data are displayed in rear. We click on Browse in order to retrieve all rear reactions. We can customize our result table by adding a column for GO terms. A column which is not visible by default but can be added. To do this we click on the customize result table button, select gene ontology and click on save. We can now see which rear reactions are mapped or not to GO term. To see how GO terms are displayed in an individual reaction page we can click on this rear reaction. The GO annotation is shown at the top of the page as well as in the cross reference section. Now let's explore how we can search rear reactions with GO terms. This can be done using the simple search box, the advanced search and the retrieve ID mapping service. To retrieve all the rear reactions which are mapped to GO we can enter GO colon star in the simple search box. We could have done the same type of query by using the advanced search. For this we click on advanced search, click on all, select gene ontology GO and enter a star to retrieve all rear reactions linked to a GO molecular function term. We will now discover the difference between the hierarchical search, the default search and an exact search. We can use the simple search to retrieve reactions mapped to a given GO identifier. For example GO colon 0051920 for peroxyredoxin activity. It returns two rear reactions which are mapped to two different GO terms. This result is due to the fact that the rear search engine performs a hierarchical search. One of the rear reactions is mapped to our query GO term peroxyredoxin activity. The other is mapped to a more specific GO, pyrroxyredoxin activity which is a child of peroxyredoxin activity. However it is possible to perform an exact search. To do this we can use the advanced search. We see that the query form is already prefilled with our GO identifier. If we click on exact search we get the rear reaction that is exactly mapped to our GO term but not to any of its child terms. Note that the query form is now filled with the prefix GO exact colon followed by the GO identifier. Another useful feature of the advanced search is the autocomplete function to help us retrieve GO terms mapped to rear by their names. Let's start typing trip. The autocomplete function suggests a list of GO terms that contain trip and that are in the list of GO terms mapped to rear reactions. We can select tryptophanedymacylalitransferase activity and click on search. It returns the rear reaction 14173. If we click on the GO term a black toolbox appears with links to the Amigo and QuickGO ontology browsers for this term. Let's click on QuickGO. In this page we can look at the ancestor chart describing the hierarchy of this GO term. We see that our GO term is in the category Molecular Function and that it has no child terms. There was no need to consider performing an exact search in this case. We can search rear with several GO terms at a time. To do so we can use the simple search box and combine our GO terms with the OR operator. However, if we have more than just a few GO terms for which we'd like to obtain the corresponding rear reactions it will be more convenient to use the ID mapping service. We click on the retrieve ID mapping link, select the identifier type genontology exact, copy paste our list into the box and click on submit. Our four GO terms map to four rear reactions. Note that the ID mapping can also perform a hierarchical search. If we choose genontology without specifying exact we can see that the four GO terms now map to five rear reactions. All the numbers shown in this tutorial will of course change regularly depending on the evolution of biological knowledge and on progressing biocuration efforts. Never hesitate to contact us if you have any questions or remarks and to look at our help pages and other videos. Thank you for your attention.