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structure/chemcomp.md

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@@ -3,20 +3,20 @@ The Chemical Component Dictionary
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The [Chemical Component Dictionary](http://www.wwpdb.org/ccd.html) is an external reference file describing all residue and small molecule components found in PDB entries. This dictionary contains detailed chemical descriptions for standard and modified amino acids/nucleotides, small molecule ligands, and solvent molecules.
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### How does BioJava decide what groups are amino acids?
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### How Does BioJava Decide what Groups Are Amino Acids?
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BioJava utilizes the Chem. Comp. Dictionary to achieve a chemically correct representation of each group. To make it clear how this can work, let's take a look at how [Selenomethionine](http://en.wikipedia.org/wiki/Selenomethionine) and water is dealt with:
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```java
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Structure structure = StructureIO.getStructure("1A62");
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for (Chain chain : structure.getChains()){
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for (Group group : chain.getAtomGroups()){
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if ( group.getPDBName().equals("MSE") || group.getPDBName().equals("HOH")){
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System.out.println(group.getPDBName() + " is a group of type " + group.getType());
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}
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}
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}
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Structure structure = StructureIO.getStructure("1A62");
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for (Chain chain : structure.getChains()){
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for (Group group : chain.getAtomGroups()){
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if ( group.getPDBName().equals("MSE") || group.getPDBName().equals("HOH")){
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System.out.println(group.getPDBName() + " is a group of type " + group.getType());
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}
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}
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}
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```
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This will give this output:
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</table>
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### How to access Chemical Component definitions
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### How to Access Chemical Component Definitions
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By default BioJava ships with a minimal representation of standard amino acids, which is useful when you just want to work with atoms and a basic data representation. However if you want to work with a correct representation (e.g. distinguish ligands from the polypeptide chain, correctly resolve chemically modified residues), it is good to tell the library to either
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1. fetch missing Chemical Component definitions on the fly (small download and parsing delays every time a new chemical compound is found), or
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2. Load all definitions at startup (slow startup, but then no further delays later on, requires more memory)
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1. Fetch missing **Chemical Component Definitions** on the fly (small download and parsing delays every time a new chemical compound is found), or
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2. Load all **Chemical Component Definitions** at startup (slow startup, but then no further delays later on, requires more memory)
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You can enable the first behaviour by doing using the [FileParsingParameters](http://www.biojava.org/docs/api/org/biojava/nbio/structure/io/FileParsingParameters.html) class:
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```java
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AtomCache cache = new AtomCache();
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// by default all files are stored at a temporary location.
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// by default all files are stored at a temporary location.
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// you can set this either via at startup with -DPDB_DIR=/path/to/files/
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// or hard code it this way:
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cache.setPath("/tmp/");
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Navigation:
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[Home](../README.md)
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| [Book 3: The Protein Structure modules](README.md)
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| [Book 3: The Structure modules](README.md)
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| Chapter 5 : Chemical Component Dictionary
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Prev: [Chapter 4 : Local installations](caching.md)
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Next: [Chapter 6 : work with mmCIF/PDBx files](mmcif.md)
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Next: [Chapter 6 : Work with mmCIF/PDBx Files](mmcif.md)

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