How Energy Is Obtained From Carbohydrates In Food

5 Feb

As promised, here is my explanation of what exactly it is that turns all the carbohydrates we eat into energy. I know it’s not exactly relevant, but it is so important in the name of food sciences and nutrition. I’m not claiming to be an expert here, just a student with a biochemistry class under my belt (and a professor that fostered an undying love and appreciation for biochemistry and the mechanics of life and metabolism). In other words, I’m a nerd. And that’s ok. I’ll try not to get too wordy- my goal is to present this material in a way that someone with a basic high school science background can understand. If you have absolutely no science background… you might struggle.

Before I jump in, I’d also like to note that carbohydrates are not the only source of energy we get from food. Fats can be broken down into fatty acids and glycerol, and proteins into amino acids, all of which by one process or another, end up in the Krebs Cycle and get turned into energy. I’m going to focus on carbohydrates because it is what my previous post was about. Maybe I’ll do a post on the others another time- fatty acids actually produce more energy per molecule than glucose!

Basically, the energy that I refer to in our body is actually ATP. That’s Adenosine Triphosphate. This molecule has a carbon backbone, but the important part is the phosphate groups. Attached to the carbon backbone are 3 phosphates, connected to each other by oxygens. There are also oxygens on the sides of the phosphate molecules. Each of these oxygens have a negative charge, and as Paula Abdul so wisely said- opposites attract. By this logic, all the negative charges repel each other. All these negatively charged oxygens trying to get away form each other creates a large amount of potential energy. If you remove even one of the phosphate groups, the molecule is much happier, and this conversion from ATP to ADP (adenosine diphosphate) is a crucial source of energy for powering life processes.

Image

So, when food is digested, if it’s going to end up as energy,the end goal is to convert it to ATP.

In food contexts, a “carbohydrate” is used to refer to a food that is rich in complex carbohydrates/sugars (cereal, bread, pasta) or simple carbohydrates/sugars (candy, jams, desserts). A complex carbohydrate is also known as a complex sugar, and a simple carbohydrate is known as a simple sugar (or what we commonly just call sugar). All this terminology gets a bit confusing because we tend to use names that have many overlapping meanings, and most people have no idea what each actually means, or what the difference is.

When carbohydrates are digested by the body, they will be broken down into their smallest form, which is glucose. Glucose is a simple sugar with the formula C6H12O6 and is very, very, very important in metabolic systems- Life would not occur without glucose! The only carbohydrates that aren’t broken down into glucose are those made up of dietary fibers, which cannot be digested.

Once you have glucose, there are a series of processes that occur to yield ATP. These are:

  1. Glycolysis
  2. Respiration
  3. Krebs Cycle
  4. Electron Transport Chain

Ok, let’s look at these.

GLYCOLYSIS: literally means break down of glycogen, this is the process by which glucose is broken down from a 6 carbon molecule into a 3 carbon molecule.

I wrote out my explanations, because I find using images so much easier to get my point across, and I didn't want to spend hours on google searching for the right one!

I wrote out my explanations, because I find using images so much easier to get my point across, and I didn’t want to spend hours on google searching for the right one!

RESPIRATION: process by which pyruvate is converted to acetyl-coA

20130205-011912.jpg

KREBS CYCLE: main source of energy production- a series reactions producing ATP and other waste products

20130205-011925.jpg 20130205-012017.jpg

ELECTRON TRANSPORT CHAIN: consists of a series of special electron carrier proteins that channel electrons from NADH to terminal electron acceptors such as oxygen. At the end of the chain, a pair of electrons are transferred to oxygen and water is formed, and the enzyme ATP synthase takes the energy of the protons to synthesize ATP.

electron-transport-chain-cpg-notes

TOTAL ENERGY YIELD

20130205-012039.jpg

…And this is all from ONE glucose molecule.

So, I hope that clears it up a little bit. Obviously, it is much more complicated than this, but at least now you have a brief overview of the process by which carbohydrates are turned into energy!

Let me know if there’s anything I can clear up for you.

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One Response to “How Energy Is Obtained From Carbohydrates In Food”

Trackbacks/Pingbacks

  1. Pre-Stamina Day Carbo-Loading « Healthy Living For the Culinary Impaired - February 5, 2013

    […] all the energy I can get. To read more about how your body reaps energy from carbohydrates, click here! (I LOVE biochemistry and I had way too much on the subject to put it in this post). But my point […]

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