A rather delicious fish and reaction rates

I try to infuse what I teach my child with wonder, humour and relevance, though it must be said, much of the International Baccalaureate Diploma chemistry syllabus for chemistry is rather dry.

I am stuck with teaching her about catalysts: energy diagrams, industrial applications, features. It’s no fun, unlike thermodynamics where we could debate endlessly about the universe, the concept of free energy and chaos.

So here goes:

Perhaps the most incredible catalysts are the biological ones, namely enzymes. They are remarkably complex and specific, often made from many thousands of atoms and a few metal ions. Enzymes are folded in such a way that they can hold the reactant molecules in their “pockets” of their complex structures, using hydrogen bonds and electrostatic forces between groups of atoms with opposite charges, to facilitate a particular reaction happening. And because biochemical reactions often happen in a series of discrete steps rather than in a simple straightforward manner, the interactions between the catalyst and the reactant molecules change with each different stage, like some molecular ballet taking place within the living body, stabilising the intermediates birthed from each pirouette. It is these multiple interactions that make enzymes so specific in their participation, and what that makes the living body truly a miracle.

You want to do an amazing chemistry experiment on catalysts? This is what you need:

1 whole fish, cleaned
Juice of 1 lemon
1 bunch of parsley, chopped
1 inch ginger, peeled and grated
Olive oil
Sea salt and freshly ground pepper
Marinade the fish in lemon juice. Leave in the refrigerator overnight. Then place the fish in the middle of a large sheet of baking parchment. Season generously with salt and pepper, drizzle olive oil generously on the fish and scatter parsley and grated ginger over it. Bake in an oven heated to 375°F for 30-40 minutes, until the flesh flakes off.

The acid in the lemon juice catalyses the breakdown of peptide chains in the fish protein in a process called hydrolysis. The H+ ions of the lemon juice (citric acid) accelerates the reaction of the amide group (-CONH-) with water, bringing about the breakage of the peptide link (C-N bond).

In fact, you don’t even need to cook the fish – for example, the Peruvian dish Ceviche – but that’s another experiment altogether; the Kadazan-Dusun folks from Borneo has a dish called the Hinava, which is pretty similar to Ceviche, and I have had the good fortune to taste it on several occasions.

baked-fish-04.jpg

Photo from recipegreat.

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