Hey Nerds,

To do well with organic molecules, all you need to know is a few facts and to recognize some specific structures. That’s it. I rewrote this article three times, and every time was more detailed than the last. It eventually became ridiculous. I started by comparing a cell to a city, then to a house, then just explaining it in terms of how it relates to the body – UNNECESSARY. So, enjoy this; it’s short, sweet, and to the point.

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CARBOHYDRATES (sugars)

• Carbon, Hydrogen, and Oxygen. All sugars that you will deal with for a long time will be made up of a combination of these three elements. Many of them will be in a ring, like those pictured above.

• Look for those elements in order to identify sugars. You can also look for a carbon backbone. Because carbon has 4 bonds, it can bond to another carbon on each side and still have room for binding to hydrogen or oxygen. Sometimes, the shape can give it away too, like glucose has six sides and ribose has five. But as you can see above, it isn’t necessary for sugars to be in a ring.

POLYPEPTIDES (proteins)

• ALL polypeptides are composed of amino acids, and ALL amino acids will have the following structure.

• There will be a Carboxyl Group, an Amino Group, a Hydrogen, and the dreaded “R-Group,” all bound to a central Carbon.

• Amino acids are the building blocks of proteins, in case you forgot. The “R-Group” is what makes one amino acid different from another; other than the R-Group, all amino acids are exactly the same.

• In order to identify a protein, look for a carbon bound to another carbon bound to a nitrogen, like in the schematic below. Although there are Hydrogens, Oxygens, and R-Groups bound to the middle ( you can ignore the arrows and dotted lines), you can see that there is a clear pattern of N-C-C-N-C-C-N-C-C-N… along the backbone of the protein.

• Your teacher may also hit you with a larger representation of a protein. Ribbons or blobs, like these pictured below, are usually proteins.

LIPIDS

• Lipids have ONLY Hydrocarbons. Can you guess the elements that make those up? Carbon and Hydrogen? YES!

• That’s all you really need to know in order to recognize them. They are the only organic molecules that are made of just hydrocarbons.

• You may need to know that squiggly lines like the ones pictured above are a shorthand way of writing carbon-carbon bonds. If you don’t see anything else written in on the squiggly line, you can assume that it’s just carbon and hydrogen.

NUCLEIC ACIDS

• Three parts: Pentose (5-carbon sugar) + Nitrogenous Base (A,T,G,C) + Phosphate Group. These have a very distinctive shape, and you shouldn’t have any trouble recognizing them because they HAVE TO bond this way to be recognized as a nucleic acid. As you can see above, it’s got a structure that should be fairly easy to recognize.

• And don’t worry about the differences between different kinds of nucleic acids, the difference comes in the TYPE of nitrogenous base that is used. The overall structure of DNA, tRNA, mRNA, and whatever other -NA that you come across will all have the same basic structure… else they wouldn’t be a nucleic acid.

So Remember:

1. Protein: carbon bonded to nitrogen bonded to oxygen. and R group.
2. Sugar: carbon, hydrogen, oxygen
3. Lipids: carbon and hydrogen ONLY
4. Nucleic Acids: sugar, phosphate, nitrogenous base.

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Best of Luck,
Grey