Structure of influenza virus

influenza-virion3In this week’s discussion of swine flu A/Mexico/09 (H1N1), we have considered many aspects of influenza virus biology that might not be familiar to some readers of virology blog. I thought it might be useful to explain how the virus multiplies, how it infects us, and how we combat infection. Today we’ll start with the basic structure of influenza virus, illustrated above.

The influenza virion (as the infectious particle is called) is roughly spherical. It is an enveloped virus – that is, the outer layer is a lipid membrane which is taken from the host cell in which the virus multiplies. Inserted into the lipid membrane are ‘spikes’, which are proteins – actually glycoproteins, because they consist of protein linked to sugars – known as HA (hemagglutinin) and NA (neuraminidase). These are the proteins that determine the subtype of influenza virus (A/H1N1, for example). We’ll discuss later how the HA and NA are given subtype numbers. The HA and NA are important in the immune response against the virus; antibodies (proteins made by us to combat infection) against these spikes may protect against infection. The NA protein is the target of the antiviral drugs Relenza and Tamiflu. Also embedded in the lipid membrane is the M2 protein, which is the target of the antiviral adamantanes – amantadine and rimantadine.

Beneath the lipid membrane is a viral protein called M1, or matrix protein. This protein, which forms a shell, gives strength and rigidity to the lipid envelope. Within the interior of the virion are the viral RNAs – 8 of them for influenza A viruses. These are the genetic material of the virus; they code for one or two proteins. Each RNA segment, as they are called, consists of RNA joined with several proteins shown in the diagram: B1, PB2, PA, NP. These RNA segments are the genes of influenza virus. The interior of the virion also contains another protein called NEP.

This week, when we discussed the nucleotide sequence of swine influenza RNAs, we were referring to these RNA molecules. Tomorrow I’ll show you how each RNA codes for protein. This way it will be easier to understand the meaning of the swine flu virus sequences that were released this week.

Let me know if this type of explanation is useful, and if you would like me to continue.

Comments on this entry are closed.

  • mdubuque 30 April 2009, 5:52 pm

    This is useful to me personally, thank you.

    So the HA and the NA are two spikes that a flu virus will use to penetrate the cell wall of a human?


  • profvrr 30 April 2009, 6:49 pm

    The HA is used to penetrate the outer cell membrane, also called the
    plasma membrane, of a human cell. The NA plays a role during release
    of viruses, as you'll see in a later post…that is if there is enough

  • Corey Philipp 30 April 2009, 6:52 pm

    I would like to see you continue to write about this. Here are a few refrences for NA and HA clarity…

    Also note the british spelling…haemagglutinin…very middle english. 🙂

  • mdubuque 30 April 2009, 6:58 pm

    Thanks so much. Your explanation was certainly extremely succinct and clear, which is quite helpful.

    Not all virologists are great writers. You are both.

    It isn't easy conveying complex subject material to those unfamiliar with a particular subject. Personally, I'm ready for the next lesson.

    But I understand your time constraints are extreme and your workload has likely spiked recently.


  • phogdog 30 April 2009, 7:18 pm

    yes and please continue

  • Trine 30 April 2009, 7:41 pm

    Hell yeah continue on…

  • Temujin 30 April 2009, 7:41 pm

    Thank you. This is not only useful to people with no background in medicine or biology, but immensely useful to somwone like me from a different background.

    I am looking forward to a continuation of this.

    I have been posting these daily updates to Facebook so other people can see them and pass them on.

  • SallyAnne 1 May 2009, 4:28 am

    Way useful. It's been about ten years since I covered any of this in detail, so while I may have known it once, I need the refresher (and besides, I don't know what's changed since I was in vet school). I'm getting questions from clients/coworkers, and this is all helping me pull all the pieces together again.

  • abdo 2 May 2009, 6:24 am

    please, i want to know what is the most important protein, which I can use for the preparation a vaccine against swine influenza
    segment 2 of virus which encoding m1and m2 which in it empeded NA or choice HA

  • avila edwin 2 May 2009, 4:48 pm

    very useful information for all the people who wants to know more about the virus, and how it is structured. I would like you to write some article about the transmission ways and how it is affecting the cities, specially mexico city. Thank you for the publications.

  • Katharina 4 May 2009, 11:07 am

    Please continue. This is an excellent site. I came here because I try to understand the differences between the various AH1N1 strains. I find it confusing that may news article refer to THE AH1N1 virus.

  • Katharina 4 May 2009, 11:13 am

    Clarification: what I find confusing is when they refer to THE AH1N1 virus in contexts where is is necessary to distinguish between various strains.

  • profvrr 4 May 2009, 11:40 am

    I agree. That is why, on my blog posts, I refer to A/Mexico/2009 (H1N1).

  • Mulubrhan 8 May 2009, 8:19 am

    Yes, please this is such a good explanation. That would be great if you could continue with you explanation.

  • JENILYNE 25 May 2009, 11:12 am


  • drsaurabh 11 August 2009, 8:38 am


  • drsaurabh 11 August 2009, 8:40 am

    it is useful.kindly continue

  • sam 12 August 2009, 6:35 pm

    continue please…

  • maheshvm 15 August 2009, 8:21 pm

    definetly usefull – please continue .

  • komalswagh 16 August 2009, 10:17 pm

    i want to information abt swine flue virology and there varous type of structures in my account

  • Name 17 August 2009, 7:28 am

    please kindly explain us the protein synthesis pathway

  • Chun-Nan Chen 30 August 2009, 10:53 am

    Absolutely. Your article is wonderfully written. I'm a molecular biologist but know very little about virology. Your article gives me a solid matrix to grow on. Please continue your good work.



  • Vanessa 6 September 2009, 2:31 am

    I am a student and I am very interested in finding out such relavant and interesting stuff although it is not covered in our syllabus. Please continue. (:

  • rohinimylavarapu 17 September 2009, 8:54 pm

    the info given by you is very much useful…….may i know about the remedies for this virus.Also may i know about the remedies present in the food which we take to become immune to this virus…..?

  • mhtjsh 21 September 2009, 4:43 am

    hi, can you please explain in what respect does influenza virus a is differnt from type B and C. In short i am curious to knw abt the virus b and c as well .

  • dd 28 September 2009, 5:24 pm

    plez…explain more
    i hve to presnt about it

  • Patriicia 6 October 2009, 2:00 am

    Please, go on!

  • Aphrodite 7 November 2009, 9:50 am

    This helped me with my school project, thanks! BTW, I have the Swine Flu

  • amy 14 November 2009, 11:58 pm

    thank you so much for this explanation.It's very useful!

  • devpriya11 20 November 2009, 11:56 pm

    Brief explanatory and easy to understand

  • Dipset on holidays 30 November 2009, 3:23 pm

    i must disagree. this quite a poor portrayal of the virus. having worked on the frontline of various influenzas i have found that your RNA polyamearse is quite incorrect. kindly work on that sir.

  • gsgs 1 December 2009, 3:04 am

    I didn't know NEP. Found it here:
    Nuclear Export Protein, NS2

    54 comments 0 likes 2 points

  • profvrr 1 December 2009, 4:05 am

    NEP used to be called NS2, nonstructural protein 2; encoded by a
    second ORF in RNA 8. Then it was found in virions, interacting with
    M1, and renamed NEP, nuclear export protein.

  • yatish kumar 18 December 2009, 12:01 am

    actually i just wana know that if we will distroy or disturbe the structure or if we remove the spikes (NA/ HA), than can the spreading of this viruse/ joining of viruse with Anitibody of host cell can b done?

  • profvrr 18 December 2009, 7:02 am

    Without HA the virions cannot attach to cell receptors and of course
    the virions will not combine with anti-HA antibodies. NA is not
    required to infect a cell, but without it, newly synthesized virus
    particles cannot be released from the infected cell.

  • Tasneem fatima 19 December 2009, 4:54 am

    hey Thank u so much…….its really v v useful…..being micro and biotech student it is highly informativ for me.thnx alot……m lookng frward for more infrmation……

  • 735019 16 January 2010, 10:46 am

    this is very good thanks…. i just have one question is the H1N1 virus a prokaryote, eukaryote, or just non-cellular?

  • profvrr 19 January 2010, 2:06 pm

    Viruses are not cellular; hence they are not classified as prokaryotic
    or eukaryotic.

  • Sally Soh 2 February 2010, 11:06 pm

    Hi! I would like to understand how mutation in the HA such as E391K in the trimerization interface may affect the effectiveness of the H1N1 vaccine.

  • chandra_cse 5 February 2010, 5:03 am

    Hello Respected Professor VRR,
    I am chandra sekhar with computer science background,Recently i started my research in bioinformatics, I am very much interested to work with influenza related data,
    Could you please suggest me any research problem to work with influenza data .

    Thanks in advance

  • ginabush 5 February 2010, 9:54 am

    thats racist

  • abimbola 4 March 2010, 4:29 am

    very useful, would like to see more updates on this.

  • Subhash Godbole 29 March 2010, 11:13 pm

    I am new in the field of Virology. I have one basic question. When we see the structure of a virus, e.g. H1N1 virus, then we find that it is quite simple. Then at structural level, what is the difference between a live virus and a dead virus ?

  • Yi-Ting Tsai 30 March 2010, 6:52 pm

    Obviously, not all viral proteins are included in the virons. I have a question, how do scientists determinate the virus structure? which proteins are included in the virons?
    There are two common categories: structure proteins and neucleoproteins. Like poliovirus protein 2B, a short peptide, can scientist certainly exclude that in the virons?

  • Yi-Ting Tsai 31 March 2010, 1:52 am

    Obviously, not all viral proteins are included in the virons. I have a question, how do scientists determinate the virus structure? which proteins are included in the virons?
    There are two common categories: structure proteins and neucleoproteins. Like poliovirus protein 2B, a short peptide, can scientist certainly exclude that in the virons?

  • Adam 25 May 2010, 11:08 pm

    Virus's arent alive so the difference between “live” and “dead” virus's is a poor question. the destinction between functioning virus's and lysed or defective/inoperative virus's is that they will not produce proteins or if they have been lysed than they will loose there membrane and their contence will be dispersed around the surrounding tissue

  • Nama Swaroopa 13 July 2010, 11:16 am

    it is very much woth enough do continue

  • Remove Spyware 7 August 2010, 4:18 pm

    Thanks for your explantion about influenza virus.

  • naincy chandan 26 August 2010, 4:56 am

    sir,is it possible that only 1 virus causes infection??can you plz justify?