Submitted by Peter Craig / McDaniel College on Tue, 07/15/2014 - 01:18
My Notes

The Diatom Thalassiosira weissflogii is very resilient.  It thrives in poor quality water, where high CO2 levels, chlorine and cadmium ion concentrations, and pH are observed.  How is it possible for cadmium ions to be a nutrient for this diatom, when it is normally seen as a toxin in biological systems?

This LO introduces students to bioinorganic chemistry using the enzyme carbonic anhydrase to illustrate biodiversity, adaptation, HASB theory, metal ion ligand bonding as represented by the PDB using Ligand Explorer, and more.

Attachment Size
CdCA LO version 3.pptx 624.69 KB
Learning Goals

Students will:

  1. be able to describe the function of three organic ligands that bind zinc and cadmium ions, namely glutathione, metallothionein and carbonic anhydrase.
  2. appreciate that different metal ions exhibit ligand atom binding preferences.
  3. be able to understand the linkage between bioavailability of elements driving survival through ligand adaptation.
  4. be able to understand the purpose of ligand metal ion binding as a way to enhance molecular functionality (carbonic anhydrase won't work without a zinc or cadmium ion present in the active site) and to prevent toxicity (having a metal ion coordinated to one of the three chelators listed under learning goal 1 above won't allow it to contribute to potential toxicity).
Implementation Notes

This is a real life example of an organism adapting to it's environment by taking what is typically a toxic metal ion and using it to allow a key enzyme to function.  This LO can be used to introduce bioinorganic chemistry and/or after learning the basics of coordination chemistry, be a summary illustration of the application of what students have learned.  This is a new LO developed at the VIPEr workshop at Northwestern University, July 2014 so it is yet to be tested.  Please do so and post your feedback.

Time Required
20 minutes
Evaluation Methods

Students should answer the following questions having participated in the PowerPoint discussion:


Associate the role of each of the following ligands in biological systems by writing either sequestering agent or enzyme after each item below:


Carbonic Anhydrase



Match the amino acid/ligand (Lewis Base) listed below with the preferred metal ions (Lewis acid) Cd2+ and Zn2+ (if you think there is no preference, state this):

Cysteine (S)

Histidine (N)

Water (O)

Bicarbonate (O)


How was the Carbonic Anhydrase “ligand” adapted to accommodate Cd2+ ions to allow diatoms to thrive in Zn2+ deficient waters?


Fill in the gaps below with either Zn2+ or Cd2+:


____ ions are thought to induce toxicity in cells by inducing oxidative stress.  ____ ions, however, are considered essential trace metal ions.

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