# 4.4a C: Essential vs. Nonessential

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What differentiates EAAs from NEAAs?&#x20;

* essential amino acids take additional steps to synthesize&#x20;
* essential amino acids have a complex r group sidechain (see red above)&#x20;

Essential amino acids (EAAs)

* Can not be synthesized by most metazoans, so they must come from the diet
* there is very low fractionation of EAAs between trophic positions&#x20;
* The ∆C of EAAs will reflect the base source of C (e.g. zooplankton, algae, etc.)&#x20;
* Can be used to assess pure routing of diet to consumer&#x20;

Nonessential amino acids (NAAs)&#x20;

* can be synthesized by metazoans by breaking up other AAs and restructuring them&#x20;
* synthesized de novo from a bulk carbon pool&#x20;
* huge amount of variability in NAAs&#x20;
* Can be used to represent pure mixing of diet into consumer&#x20;

Amino Acid C isotope fingerprinting&#x20;

* every source that can synthesize EAAs leaves a specific  fingerprint, or ratio, of the EAAs based on the biosynthetic pathways involved in making the EAAs&#x20;
  \*
* Currently very broad - because most plants use the same pathways, we group them all together.&#x20;
* End members will have very specific fingerprints that can be seen to segregate using a PCA&#x20;