Update datanodes.Rmd

fix image issues. 

Image path should be ".png" not ".PNG"

datanodes.Rmd

@@ -14,19 +14,19 @@ knitr::include_graphics("images/screenshots/datanodes.png")
 
 ## Molecular DataNodes
 
-### GeneProduct      ![](images/figures/datanodes/geneproduct.PNG){width=300}
+### GeneProduct      ![](images/figures/datanodes/geneproduct.png){width=300}
 An entity representing any product of a given gene, including DNA, RNA and Protein. This is the most generic representation of a gene-based biomolecule and is useful when more than one representation might be useful in the given context
 
-### Metabolite      ![](images/figures/datanodes/metabolite.PNG){width=300}
+### Metabolite      ![](images/figures/datanodes/metabolite.png){width=300}
 An entity representing a metabolite, including chemical compounds that participate in or are produced by metabolic reactions, but also other chemical compounds that participate in a pathway otherwise.
 
-### Protein      ![](images/figures/datanodes/protein.PNG){width=300}
+### Protein      ![](images/figures/datanodes/protein.png){width=300}
 A biomolecular polymer of amino acids, translated from mRNA.
 
-### DNA      ![](images/figures/datanodes/dna.PNG){width=300}
+### DNA      ![](images/figures/datanodes/dna.png){width=300}
 An entity representing a DNA polymer. 
 
-### RNA      ![](images/figures/datanodes/rna.PNG){width=300}
+### RNA      ![](images/figures/datanodes/rna.png){width=300}
 An entity representing a RNA peptide, including mRNA, miRNA, etc. This is commonly used to explicitly represent mRNA transcripts (excluding DNA or protein forms) or other RNA species, like miRNA, exRNA, lncRNA, etc
 
 ### Complex (deprecated)
@@ -36,22 +36,22 @@ The Complex Data Node Type is deprecated. Its use was similar to that of [Alias]
 
 ## Concept DataNodes
 
-### Pathway      ![](images/figures/datanodes/pathway.PNG){width=300}
+### Pathway      ![](images/figures/datanodes/pathway.png){width=300}
 A biological process representing a set of interactions and relationships among genes, proteins, metabolites, and other factors in the context of cellular compartments, tissues and organisms.
 
-### Disease      ![](images/figures/datanodes/disease.PNG){width=300}
+### Disease      ![](images/figures/datanodes/disease.png){width=300}
 
-### Phenotype      ![](images/figures/datanodes/phenotype.PNG){width=300}
+### Phenotype      ![](images/figures/datanodes/phenotype.png){width=300}
 
-### Alias       ![](images/figures/datanodes/alias.PNG){width=300}
+### Alias       ![](images/figures/datanodes/alias.png){width=300}
 An Alias is a special type of Data Node which can represent a Group pathway element (or other entity). Please see [Aliases](#aliases) for more information!
 
-### Event      ![](images/figures/datanodes/event.PNG){width=300}
+### Event      ![](images/figures/datanodes/event.png){width=300}
 
-### CellNode      ![](images/figures/datanodes/cellnode.PNG){width=300} 
+### CellNode      ![](images/figures/datanodes/cellnode.png){width=300} 
 
-### Organ      ![](images/figures/datanodes/organ.PNG){width=300} 
+### Organ      ![](images/figures/datanodes/organ.png){width=300} 
 
-### Undefined      ![](images/figures/datanodes/undefined.PNG){width=300}
+### Undefined      ![](images/figures/datanodes/undefined.png){width=300}
 An unspecified biological entity or factor. Should only be used if the type is truly unknown or is different from the ones covered by other data node types.