Molecule of the Month: Something Sweet.

You may recall the most recent Molecule of the Month post on salt (NaCl).  If not, you'll be happy to read this brief paragraph summarizing what FTDM's "Molecule of the Month" theme is all about. Molecule of the Month is a series of posts that take a molecular look at materials we use in every-day life.  Last time I discussed that white stuff we tend to sprinkle on our eggs and rice (salt).  This time I'll be discussing the white stuff we tend to sprinkle on our all-bran cereal or in our coffee (sugar).  

Perhaps next time I'll discuss the white stuff that leads to horrific addiction and physical/mental deterioration...

Why do salt and sugar look the same, but taste completely different?

Which one's which?   The left is salt, the right is sugar, but why do they look the same? Photo credit: lifechirocenter.com and glutenfreeschool.com

Which one's which?  
The left is salt, the right is sugar, but why do they look the same?
Photo credit: lifechirocenter.com and glutenfreeschool.com

The two look the same in larger quantities because they both form crystalline structures in a similar way.  What this means is that the molecules themselves stack on each other in a similar form.  To put it another way, think of two skyscrapers - they may look the same on the outside, but walk in the buildings and they each have entirely different interior design.  This "interior design" corresponds to the chemical structures of salt and sugar:

A molecular look at the same substances. Again, salt on the left, sugar to the right. Photo credit: SDSU and spaceref.com

A molecular look at the same substances. Again, salt on the left, sugar to the right.
Photo credit: SDSU and spaceref.com

These chemical structures are what give salt and sugar their respectively salty or sweet properties. Salt is ionic, while sugar is a carbohydrate.  This distinguishes the two enough such that, when one or the other touches your taste buds (where specific receptors await), you perceive a salty or sweet flavor. Imagine your tongue with hundreds of small locks (receptors) to doors (of flavor perception). Some of these locks are opened by one key (salt) and others are opened by another key (sugar).

That's why, even though salt and sugar may look the same at a glance, we taste them differently.

Why do we crave sugar?
I've alluded to why this is the case in a previous post, but to put it simply: our body needs sugar to function.  Carbohydrates (a group that sugars belong to) are one of four essential molecule types for all life.  Sugar, in particular, plays a key role in multiple metabolic pathways (which are processes occurring in each cell of our body that allow us to live each day).  

Sugar acts as one source of energy for these metabolic pathways to take place, which is why we (literally) feel more energetic after eating.  However, many studies have shown that too much sugar is just as bad.  We see this in diseases such as diabetes and heart disease.

What's in sugar-free foods that cause them to taste sweet?
Sugar-free foods, like sugar-free gum or diet soda, typically contain synthetically-designed chemicals that mimic sugar's properties, but are structurally different.  What is meant by this is that they still fit the locks on your tongue where sugar would usually fit, but they're not sugar.  Think of them sort of like skeleton keys in that they open the same sugar "locks", but they don't look like sugar.  Nearly all sugar alternatives (eg high-fructose corn syrup or artificial sweetners) are bad for us because our body is trying to digest/metabolize them as if they were sugar, but they're not.  Too much of these sweetners have an amplified negative impact on our health in comparison to too much sugar on its own.

With all of this said, it's absolutely fascinating how one molecule, sugar, can have such a big effect on our lives.  Hopefully this article gave us all a little insight into what sugar is about on a molecular level.

Stay hungry !