Friday, May 21, 2010

Independent Functions of Viral Protein and Nucleic Acid in Growth of Bacteriophage

Aka, deoxyribonucleic acid (DNA) is the genetic material! This journal article, published in 1952 by Alfred Hershey and Martha Chase, is a landmark discovery in molecular biology. I won't go into the gritty details, but I will offer some background and the basic gist of the experiment. (FYI, it's not the anniversary of its publication or anything--I'm just really excited that the .pdf is available online for free :-) )

At the time, no one knew exactly what passed on genetic information. By the 1950s, it was between DNA and proteins, and most scientists figured the latter were the molecules of life. It made the most sense, since proteins are far more complex than DNA--proteins can be made up of up to 20 different amino acids, whereas there are only four nucleic acids in DNA.

Hershey and Chase wanted to see what a virus used to infect bacteria (the "infectious material"). They labeled the proteins in one batch of virus with radioactive sulfur, and the DNA in another batch with radioactive phosphorus. They let the viruses hang out with the bacteria for a little while, then tested to see which batch of bacteria had labeled material. They discovered that the only bacteria with radioactive material were the ones that had been infected using viruses labeled with phosphorus--basically, DNA, not protein, was being used to pass on genetic material from virus to bacterium. Here is a diagram that does a way better job illustrating what I'm trying to explain:

The main reason why this experiment is extremely cool is that, despite the incredible importance of the findings, it is very simple and straightforward. A lot of the most revolutionary discoveries in science have been made with very simple but elegant experiments. Also, this was one of the first important biology papers coauthored by a woman (I think), so that's pretty neat too.

I have to confess that the main reason why I decided to post this is because I love how, after trying all sorts of high-tech, lab-ey ways to separate the viruses from the bacteria, Hershey and Chase settled on a plain kitchen blender...oh yeah.

Further reading

For the experiment:
Wikipedia page.
Independent functions of viral protein and nucleic acid in growth of bacteriophage (Hershey and Chase, 1952). [pdf]

Two more simple but very cool and important molecular biology papers:
A Structure for Deoxyribose Nucleic Acid (Watson and Crick, 1953). [pdf]
The replication of DNA in Escherichia coli (Meselson and Stahl, 1958). [pdf]

[Diagram of experiment taken completely without permission from The Pauling Blog.]

Friday, May 7, 2010

Smallpox (a cheerful post)

Below is an article I originally wrote for the school paper science/tech page and beefed up for this blog. It's a bit awkward, but I feel like I did a decent job. Another random post, and I don't care. Huzzah!

Poxviruses are the biggest and most complex animal viruses. The human poxvirus, smallpox, was one of the major causes of death in many civilizations for a long time. Smallpox killed about 500 million people in the 20th century—far more than the deaths caused by wars, the 1918 flu pandemic, and AIDS combined. Famous victims include Ramses V, Mozart, Beethoven, George Washington, Andrew Jackson, Abraham Lincoln, Joseph Stalin, Mary Queen of Scots, Mary II of England, Louis XV of France, and Peter II of Russia.

The ordinary form of smallpox has a 30% mortality; however, two other types, the flat and hemorrhagic manifestations, are almost always fatal. The disease is characterized by rounded vesicles that are usually dimpled, and found mostly around the head and extremities. The bumps have been described as feeling like BB gun pellets embedded in the skin. Many survivors are badly scarred or even blinded.

There have been attempts to prevent or lessen the impact of a smallpox infection via inoculation for centuries. All sorts of methods have been used, from inhaling ground up scabs to introducing the virus through cuts in the skin. Though death from these sorts of infection was still possible, the mortality was far lower and thus worth the risk.

In 1796, Edward Jenner began experimenting with vaccination by purposely infecting an eight-year-old boy, James Phipps, with cowpox, a bovine virus related to smallpox. It was fairly well-known in rural areas that milkmaids rarely contracted smallpox, and Jenner wanted to investigate this. After contracting cowpox, little Phipps was mildly ill (a low fever and some pox for about a week), but showed no sign of infection after being exposed to smallpox later on. It turns out that cowpox confers immunity to smallpox. To put it simply, the body learns how to handle smallpox infection by being exposed to its mild-mannered cousin. Nowadays this experiment by the "father of immunology" would be considered unethical, but at the time his discovery was revolutionary. Jenner tested several other individuals, published his work, and led an effort to develop a vaccine for smallpox made from the pus of cowpox bumps.

Thanks to the work of Jenner and other pioneers in the field, a vaccine was developed. At first, vaccines were often contaminated and sometimes caused health problems, but once again, the benefits far outweighed the rare serious side effects. During the 19th century, many countries declared smallpox vaccination mandatory. Once mass vaccination became commonplace, the rates of smallpox infection in developed areas plummeted.

In 1967, the World Health Organization (WHO) made the decision to attempt worldwide eradication of smallpox. The disease is an excellent candidate for eradication for several reasons. First, it is exclusive to humans, so there is no animal carrier. There is a very effective, inexpensive vaccine against it. People are not carriers for the disease once they get over it. And finally, cases of smallpox are easily identifiable, thanks to the distinctive bumps and rash pattern.

At this time, vaccination was widespread in developed countries, so WHO efforts were concentrated in third-world countries. Vaccination ended in the United States in 1972 because of the incredibly low incidence and the possibility of severe side effects.
Rather than try to vaccinate all members of the global population, the WHO decided to address individual cases. Cards with photos of infected individuals and a basic clinical description of the disease were widely distributed. When a case of smallpox was identified, the WHO was contacted. They then put the infected individual in isolation and vaccinated all people in the general area, a process called “ring vaccination.” Once cases became less common, cash rewards were offered for reporting sick individuals. The last natural case occurred in Somalia in 1977. The world was officially declared smallpox-free in 1980.

Though smallpox is no longer found in the wild, it does exist in two laboratories, the CDC in Atlanta and the Vector Institute in Koltsovo, Russia. The virus is important to keep in the laboratory. Even though it is not necessary for vaccination against the disease, it is useful for research in development of antivirals and other vaccines. The decision to maintain the virus in the laboratory has been a controversial one. There is the distinct risk of it somehow making its way out of the laboratory, since smallpox is an excellent biological weapon.

Smallpox as a Biological Weapon
A good biological weapon doesn’t just cause suffering—it makes a society fall apart. Smallpox kills or permanently scars most who are infected. It is highly contagious, and because we no longer vaccinate against it, most people have no immunity. In the event of a widespread smallpox epidemic without emergency vaccination, people would not go to work, a general fear would pervade communities, children could not go to school, and even the government might begin to shut down.

Smallpox as a biological weapon would not be a new phenomenon. For instance, Cortez inadvertently wiped out a good portion of the Aztec population because of one infected member of his expedition. The British in the French and Indian war gave Native Americans blankets that had been in contact with people who had smallpox, though it is unclear how effective it was. There is also some evidence that smallpox was used in the American Revolutionary War.

It is frightening to think how a disease like smallpox could disable our society. Fortunately, our country is not entirely susceptible to smallpox as a bioweapon, since enough vaccine has been stored to protect the entire population in the event of an attack.

So far, smallpox is the only disease to be fully eradicated. There have been other eradication programs that were abandoned (hookworm, malaria, yaws, and yellow fever) and a few others that are ongoing (poliomyelitis and dracunculiasis). Other potential candidates are measles, mumps, rubella, tapeworm, and filariasis.
People who are against the idea of vaccination in general often do not realize that vaccines against smallpox, polio, influenza, measles, and rabies have saved millions of lives. Yes, there are occasional side effects with all of these vaccines, but the benefits acquired by disease prevention greatly outweigh the negative consequences of mass vaccination.

Inhabitants of developed countries tend to forget that less developed or more densely populated countries have huge problems with all of these diseases. Diseases that seem rare and basically harmless can be huge threats in third world countries, where adequate nutrition and proper medical care are not always available. For instance, measles, a childhood disease that hasn't been common in a long time, has a 28% mortality rate in third-world countries. TWENTY-EIGHT PERCENT. In order for a disease to be completely eradicated, there has to be immunity on a global scale. The complete eradication of smallpox, which for millennia was a significant problem, is an amazing feat for mankind. It has shown that with a strong, organized effort, much human suffering and death can be avoided.

Monday, May 3, 2010

Roniopplemary Chicken...

This recipe was inspired (okay, stolen) from the Food Network website with, of course, several modifications from me (here is the original version). It looked simple and pretty tasty, and I happened to have all of the ingredients (yay!), so I decided to make it.

As usual, I did not have any of the ingredients in the right proportions, but whatever:

  • 3 chicken breasts
  • 1 apple, peeled and chopped
  • 1 onion, chopped
  • Garlic
  • ~2 spoonfuls of rosemary
  • Lemon juice
  • Low sodium chicken broth
  • SALT

This was quite good! I served it on white rice and consumed it over a few days. It could have used more flava, but I just heaped on the salt and everything was fine (that's what happens when you accidentally purchase low sodium chicken broth...). This recipe did have something missing though, and I'm not sure what it was. It needed richness, a sort of "umami" type of taste...whatever.

Things learned:

  • Put in the apples closer to the end. Otherwise, they get way too mushy.
  • The lemon juice was definitely a mistake. Too much acidity. I will not be using it again in this recipe.
  • Chicken CANNOT be cooked for very long. I don't know why I keep making this mistake, but I am determined not to mess up again. From now on, 2.5 hours on high, tops.
  • Less broth. It makes the rice soggy. I have yet to figure out how to get everything in Gretel thoroughly cooked without filling it with liquid (I don't want EVERYTHING to be a watery soup...). For now, I'm just using a slotted spoon to filter out liquid before I put stuff away in a tupperware.

Re: the name. Nothing else has occurred to me...there must be a name less cumbersome than "roniopplemary" out there, but it continues to evade me.

Happy May to everyone!

And happy birthday to my wonderful father!!!!!!