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Chemistry (including Biochemistry)/Difference Between LA and ALA


Hi Trista,

I've read that linoleic acid has almost the same structure as alpha linolenic acid except that there is a carbon to carbon double bond at the third carbon position for the latter.

A few questions.

1. Why are the names so close?  Who came up with the names of the compounds?  It can be confusing to adults like me, that "n" makes a lot of difference, LOL.

2. Why is the word "alpha" before linolenic acid?  Is there such a compound as linolenic acid?  If so, what would be the difference between the two compounds?  (I see the word "linolenic acid" used on the net quite often, but when I try to find the structure of linolenic acid, only alpha linolenic acid shows up.)

3. Why does the double carbon bond in question here make such a big difference in the way the body uses these two compounds?


Background info on me :- I'm 60 and have hypertension. I've had mixed success using fatty acids to control BP. I need to brush up on my organic chemistry to try to understand the literature on the subject.  The last time I studied organic chemistry was in High School, did pass, though :-)

Hello Usuf! Thank you for the background; it does help in answering the question!

1) There is an international meeting of chemistry societies called IUPAC, or International Union of Pure and Applied Chemistry. Historically, these folks are the ones that come up with all the names. ( This is done so that chemists everywhere have a 'background language' that will always refer to the same molecules, no matter what the native language of the chemist is.

That said, learning IUPAC nomenclature is a royal pain in the butt for most modern organic chemistry students. :) I'm not sure when IUPAC started being taught in schools, but it may be you escaped that rite of passage when you went through your education. (Also, for some students in the 'old days' elements were compared to the mass of carbon as opposed to the mass of hydrogen in general chemistry... which might be a surprise to you, but is hopefully not a big change.)

Much of the time IUPAC naming conventions result in Very Long Names indeed. The human tendency to create nicknames for these long names is what's tripping you up... as well as common historical names for things. It can be a big headache.

Anyway, why are the names so close? It's because the structures are very similar.

Both α-Linolenic acid and linoleic acid both describe 18 carbon chain fatty acids, with a carboxyl group on one end.

Stearic acid (IUPAC: octadecanoic acid) is the C-18 version with no double bonds. Its name is nice and unfussy because we don't have to keep track of where those double bonds are. (Also notice that it's a --anoic acid, which tells organic chemists it has saturated hydrocarbons. If had a double bond, it would be --enoic acid... with more than one double bond, it's a --dienoic (two) or --trienoic (three) acid. :)

So, Linoleic acid. IUPAC: 9,12-Octadecadienoic acid. Translating the IUPAC name, we'd read that as 'eighteen carbons, two double bonds, oh yeah, must be on that 9 and 12 carbon, and it's a carboxylic acid. Got it.' 'Proper' IUPAC naming numbers carbons from the carboxy end. Most folks count from the OTHER end and so it is a c-6 polyunsaturated omega fatty acid. (more on omega-sixes in a minute.)

Head hurt yet? Sorry, got a couple more. Please bear with me.

α-Linolenic acid has the IUPAC name 9,12,15-Octadecatrienoic acid. --oic acid means 'carboxylic acid'. 'octadeca' means eighteen carbons. 'trieneoic' means three double bonds. Those numbers indicate the first carbon of the double bond counting from the carboxylic end (the most exciting bit) of the molecule.  However, most folks look at this molecule and cheer, because this is an omega-3 fatty acid. (Its first cis double bond is on c-3.)

Why do we care about omega 3 fatty acids? Because humans can't make them, and therefore we have to find them in our diet and eat them. :) Doctors care less about omega sixes and omega nines, because humans CAN make those. Taking extra can be sometimes helpful, but isn't vital like omega threes.

But Dr. Trista, why is the alpha important?

Remember the whole 'historical names' and 'shortened names' thing? Back in the day, chemists isolated α-Linolenic acid first, thinking it sufficient to describe a c-18 carboxylic fatty acid with three cis double bonds. Then they found beta, which was an artifact, and then γ-Linolenic acid, which also had three double bonds... but those were at c6, c9, and c12. And some folks used 6,9,12-octadecatrienoic acid as a folk remedy for issues. So they needed separate names. But only α-Linolenic acid had the magic omega three. ;)

While I didn't do all your questions in the precise order, I hope this made sense. Please feel free to come back with more questions. :)

Wikipedia articles I referenced: (The 3d rendering on this page looks like a matchstick. :) (Check out this curved snake structure! :) (Oh look, a carbon horseshoe! :)

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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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