Molecule of the Month: Anthocyanins

Those who have read my previous posts know that I have a bad habit of writing about three topics on FTDM:
- Biochemistry
- Marine organisms
- Food

In today's post, I'd like to introduce another topic: plants (cue dramatic horror music).  

In efforts to continue the Molecule of the Month theme and with autumn in the air, I thought you may appreciate learning about a group of molecules known as anthocyanins.  

How are anthocyanins and autumn related?
Many of us know of trees (deciduous) in parts of the world (temperate climates) that change color around this time of year, informing us that summer is officially over. The leaves transition from green to purple/red/orange/yellow to brown before falling off and leaving the tree bare. This process takes anywhere from a few weeks to months. When all the leaves have fallen, we know that winter is upon us. This is where anthocyanins come in.

As photoperiod shortens, trees are triggered to slow down photosynthesis. Trees do this because they want to conserve energy production, and photosynthesis is the primary metabolic pathway in trees responsible for energy production. To put it another way, imagine a grizzly bear stocking up on salmon so that it has enough fat (which serves as energy storage) to survive the winter. Now think of the tree as the grizzly bear, sunlight as the salmon, and chlorophyll (crucial to photosynthesis, reside in chloroplasts) as the fat for the winter. Like grizzly bears, trees need to conserve their energy for the winter, which is why we see this physical (and metabolic) change take place with their leaves.

This image shows how light is converted to energy by chlorophyll in greater detail. Photo credit: Science News

This image shows how light is converted to energy by chlorophyll in greater detail.
Photo credit: Science News

The high abundance of chlorophyll gives the leaves their intense green color. As days get shorter, the trees are prompted to "suck" their chlorophyll gets back in by leaving "helpers" like anthocyanins behind. These leftover "helpers" in photosynthesis energy storage result in the intense colors we see during autumn.  

A zoomed in cross section of a leaf shows the various molecule groups (chlorophyll, carotenoids, and anthocyanins) involved in the photosynthesis and pigment of tree leaves in conjunction with their location in plant cells. Photo credit: USDA Forest Service

A zoomed in cross section of a leaf shows the various molecule groups (chlorophyll, carotenoids, and anthocyanins) involved in the photosynthesis and pigment of tree leaves in conjunction with their location in plant cells.

Photo credit: USDA Forest Service

What are anthocyanins?
Anthocyanins are pigments involved in photosynthesis and the absorption of light by leaves. Their colors can range from red to blue, depending on pH (more acidic = more red, more basic = more blue).  

Typical structure for an anthocyanin molecule. Photo credit: NEUROtiker

Typical structure for an anthocyanin molecule.
Photo credit: NEUROtiker

Research on anthocyanins, and other pigments found in trees, has been ongoing for decades - and has shown to serve extremely useful.  For example, the pH paper that many of us have used at one point or another in our chemistry lab courses contain litmus, which is a combination of pigments (including anthocyanins) derived from lichen.  Additional purposes for anthocyanins involve coloration for food, clothing, and other materials.  It's hard to forget about the importance of anthocynanins when they're literally all around you. 

Until next time, stay hungry!

Additional resources on anthocyanins:
- Anthocyanins as Food Colors 
- Anthocyanins in Cardiovascular Disease
- Anthocyanins and Human Health
- Chemical Studies of Anthocyanins