Immune System quiz

Answers to the questions

1. Provides an immediate nonspecific immune response.

First line of defense is like a moat and high stone walls of castle.

1)    Mechanical barriers: skin, mucosa

2)    Chemical barriers: The skin and mucous membranes secrete proteins such as lysozymes or hydrochloric that kill the germs

3)    Biological barriers: Living organisms in the body that compete with pathogens.

 

Once the invaders (bacteria, virus, or parasite etc) enter through the cut and get into the body, they would then encounter the second line of defense.

Inflammatory response is the first response to infection or injury and is the same regardless of the type of pathogen.  Inflammation is triggered by chemicals called cytokines and histamines, which are released when tissues are damaged. The cytokines and histamines cause changes in the damaged tissue. The changes help remove the cause of the damage and start the healing process. Another role of cytokines is to attract leukocytes to the site of inflammation. Some leukocytes are nonspecific and respond in the same way to most pathogens. Nonspecific leukocytes include monocytes, macrophages, neutrophils, eosinophils, and basophils. Monocytes, macrophages, and neutrophils destroy pathogens in the blood and tissues by phagocytosis. Phagocytosis is the process of engulfing and breaking down pathogens and other unwanted substances. In addition to phagocytosis, both monocytes and phagocytes produce chemicals such as cytokines that cause inflammation and fever. A fever is a higher-than-normal body temperature that may help fight infection.

<phagocytosis by a macrophage>

 

 

2.     Activates T and B cells in response to an infection

1.    B-cell activation in Humoral Immune Response

B cells are responsible for the humoral  immune response. The humoral immune response takes place in blood and lymph and antibodies are produced by activated B-cells, ‘plasma cells’.

 

2) T-cell activation in cell- mediated immune response

Activation of T-cells needs other cells help. B cells or leukocytes such as macrophages engulf pathogens in phagocytosis and display parts of the pathogens’ antigens on their surface. The cells are then called antigen-presenting cells. When a naïve T cell encounters one of these cells with an antigen matching its own, it begins the activation process. After T cells are activated, the various types of T cells play different roles in the immune response.

3.    Responds to a later exposure to the same infectious agent

The immune response is specific to a particular pathogen, and it allows the immune system to “remember” the pathogen after the infection is over. Memory cells are activated B or T cells that retain a “memory” of a specific pathogen long after an infection is over .If the pathogen tries to invade the body again,  the immune system can launch a much faster, stronger attack. This lets the immune system destroy the pathogen before it can cause harm.

4. Disinguishes self from nonself

Immune cells do not actually recognize and respond to pathogens but to the antigens (antibody + generator) they carry.  Antigens are protein molecules that the immune system recognizes as nonself. Antigens include proteins on pathogens, cancer cells, and the cells of transplanted organs. Both B and T cells can “recognize” specific antigens because they have receptor molecules on their surface that bind to particular antigen molecules or pieces of antigen molecules. As shown in the figure, the fit between a receptor molecule and a specific antigen is like a lock and key. Receptors on each B or T cell recognize and bind to just one type of antigen. The human body makes lymphocytes with receptor sites for a huge number of possible antigens that may be encountered throughout a person’s life.

 

Endorphin

     It is unfortunate that the society shows no mercy to narcotics, but what if the human body secretes one that is about fifty times more potent than heroine? Endogenous Morphine, better known as Endorphin, is a peptide hormone mainly released from the pituitary gland located in the base of the brain. Endorphin is secreted when we are under severe stress, fear or pain. It helps us forget the pain and control our emotions by interacting with the receptors of the cells. In fact, endorphin is so potent that it doesn’t simply alleviate pain but literally makes us high-- How awesome is that? Particularly famous is a state known as ‘Runner’s high’ where an exhausted athlete suddenly experiences a feeling of euphoria due to endorphin release. Endorphin also helps mothers endure immense pain when giving birth. Scientists say that many near-death experiences those religious frauds always blab about may also be a product of endorphin release. No wonder that endorphin is released to its max when you’re dying.

     In those days when our biological ancestors lived in the wild, it was necessary that they withstand stress and pain following physically demanding tasks like running and hunting. Therefore a certain group of mutants that somehow happened to have Endorphin would have been able to survive better, leaving their awesome genetic trait to humanity. In short, it’s survival of the fittest all over again.   

Lactic Acid Fermentation

Kimchi
(Source: http://c.ask.nate.com/imgs/qrsi.php/11793224/21217261/0/1/A/17c782b771bb9b8a2768bbaebf4269ca.jpg)


     Unlike what many foreigners think, Kimchi actually has a sour taste. Kimchis that can be found in grocery stores of America are in many cases something what's called 'Raw-Kimchi', a type of Kimchi that hasn't fully undergone fermentation. Where does this sour taste come from? How is the process of fermentation related to Kimchi's unique sourness loved by many Koreans?

     Glycolysis, the first step of cell respiration in which a glucose (C6H12O6) splits into two pyruvates (C3H4O3), is anaerobic, meaning that it is capable of occurring without oxygen. Anaerobic respiration however undergoes a completely different path from that of aerobic respiration which eventually generates about 38 ATPs. Fermentation is one type of anaerobic respiration. Fermentation also generates certain amount of ATPs, 'recharging' the used up NAD+s to once again form NADH. In aerobic respiration, these NADHs can later on give up electrons to oxygen to eventually generate H2O. But in anaerobic respiration, as its name suggests, there exists no oxygen within the system that can accept electrons.

   
   (Source: http://blog.naver.com/dbok1234?Redirect=Log&logNo=110165450698)

Once again take a look at the chemical equation of anaerobic glycolysis:

C6H12O6 + 2NAD+ -> 2C3H4O3 + 2ATP + 2NADH + 2H+


Without O2, the 2NADH and 2H+ undergoes what's called lactic acid fermentation. A total of 4 H+s, two of which dissociated from NADH, attaches to two pyruvic acids (two each) to form lactic acid (C3H6O3). Lactic acid is what gives a sour flavor to fermented foods including Kimchi, cheese and yogurt. Making all this happen are lactic acid bacteria better known as lactobacillus. The presence of lactic acid Bacteria is crucial to fermentation. Without lactobacillus, A food would undergo putrefaction, or simply rot instead of fermentating.

(Source:  http://www.computescotland.com/acrylamide-offset-by-lactic-acid-bacteria-3652.php)

The Strange Case of Hwang Woo Suk

 

                                                               Hwang Woo Suk (1952~)

     Unfortunately, many Koreans including I associate stem cells, the greatest asset of modern science, with one of the most scandalous incidents of fraud in human history. A sequence of revelations and the ensuing national delirium has showed how science, when combined with blind nationalism and dirty political calculations, can push one nation into an abyss of irrationality.
     It was 2004 when Hwang, a professor/researcher of Seoul National University, announced that his team was successful in culturing an embryonic stem cell from a cloned human somatic cell. This seemingly groundbreaking achievement, outlined in a 9 page paper published in <Science> (http://www.sciencemag.org/content/303/5664/1669.full.pdf), gave Hwang a literally untouchable reputation as a national hero. Hwang's method of creating an embyonic stem cell was a classical one that extracts the embryo from a zygote (This means that Hwang's method, regardless of the all scandals and scams involved, was to soon become outdated whatsoever, along with the discovery of the innovative iPSC method.) Awed by this seemingly unforeseen technology and the new possibilities sprouting from it, Koreans lavished almost unconditional support to this powerful figure. There were even talks about adding his success story in middle school textbook. That pretty much explains itself.
     In 2005, a group of young scientists in an online community named BRIC raised questions about the pictures used in Hwang's 2004 paper. Apparently the pictures used in Hwang's paper were all identical, merely a set of photos taken in different angles. As the doubt rapidly spread online, Hwang's team promptly announced that everything was a minor 'mistake', and claimed that they have already informed <Science> about this error. These excuses later on turned out to be flagrant lies. The entire nation was divided into two. Many politicians and mass media zealously defended Hwang, condemning the doubters as traitors to the nation. Many scientists and experts who either questioned or criticized Hwang were often blackmailed by his advocates. Engulfing the country was Fascist madness that, no matter what Hwang has done, every Korean should all support this hopless fraud and cheat. Eventually after a sequence of honest testimonies given by many courageous whistle-blowers, Hwang was virtually ostracized from the Korean scientific community.
      This shameful incident was literally an atomic bomb dropped on Korean society. Perhaps the ugliest aspects of Korea were revealed to the world--moral hazard of scientists who refused to seek the truth, corrupted politicians who advocated Hwang for political purposes, incompetence of the government to resolve the situation, academia's negligence in scientific verification, and above all, the Korean people's tendency of extreme nationalism. We have seen through this incident how the interference of nationalism in science can cause unimaginably detrimental consequences. Science should always exist as science. "Science knows no country, because knowledge belongs to humanity, and is the torch which illuminates the world." (Pasteur).   

Stem Cell 101

1.  The type of stem cell which the article mainly discusses is the embryonic stem cell. Sperm and egg undergo fertilization form a zygote. A zygote then divides into many cells through cell division, and these cells form what's called embryos after division and differentiation. It is after differentiation that each embryo acquires a specific function, only able to form certain cell types such as muscle or bone. The scientific principle behind stem cells is that this embryo, once not having underwent differentiation, is capable of becoming any of the 220 cell types in the human body. By extracting those 'pluripotent' embryos and growing them seperately, we are able to obtain the embryonic stem cells which can be used to regenerate damaged tissues and organisms.
     Another type of stem cell, perhaps the more orthodox and uncontroversial among the two, is the adult stem cell. Adult stem cells are yet undifferentiated cells that are capable of differentiating into specific organisms if necessary. Unlike embryonic stem cells, adult stem cells inherently exist in the human body (usually in the marrows) in extremely small amounts, and are incapable of forming all cell types with no limitations. One renowned example of an adult stem cell existing in our bodies is the Hematopoietic Stem Cell, widely used in bone-marrow transplantation among leukemia patients.
     The newly developed  iPCS perhaps epitomizes the cutting edge stem cell technology of the era--iPCS, first found by Prof. Yamanaka of Kyoto University, refers to the specially manipulated somatic cells that are literally 'reprogrammed' to function as differentiable embryonic cells. Enabling such is the transplantation of embryonic genes into the somatic cells through the use of retroviruses, the 'carriers' of the genes. The efficiency of iPCS method is an absolutely unparalleled one, for conventional methods of reprogramming involed an extremely elaborate process by which the genetic material from an adult cell is injected into an egg cell whose DNA has been removed.

2. Though it requires great precision, cloning, in its essence, is an extremely straightforward process. First you remove the nucleus from the fertilized egg, and replace the removed nucleus with a nucleus obtained from a cell of another living organism. Since the DNA information of the egg would then also be replaced with that of the nucleus donor, the offspring generated afterwards would be the exactly identical 'clone' of the donor.

3. The ethical question regarding stem cells is whether we should view the embryo as a seperate, independent living organism. The embryo itself is often destroyed when its pluripotent portion is extracted and seperated. Many Christians (mainly the Catholics) have spearheaded the anti-embryonic stem cell movement for they view an embryo as a basic form of life with spirit, and therefore believe that the destruction of such embryo is equivalent to murder. However, as the innovate iPCS method has rised, many of the ethical controversies about stem cells have generally diminished.
+Egg donor problem; black market? --also solved thanks to iPCS

The Human Genome Project

(image source: http://www.flickr.com/photos/askpang/9251502638/sizes/c/in/photostream/)

     As surprising as it sounds, we, the mankind, have made it possible to sequence entire genomes, by virtue of the groundbreaking advances in DNA sequencing technologies. The beggining was modest: biologists at first worked on interpreting relatively small genomes like bacteria and viruses. In 1996, biologists successfully discovered that the DNA sequence of the common bacterium Escherichia Coli, contains 4,639,221 base pairs (Wikipedia s.v. Human Genome Project). Then how many base pairs does the human genome contain? Over 6 billion.
     Despite the overwhelming numbers, scientists from all around the world have made rapid progress ever since they embarked on this grand scheme in 1990. The final goal of the human genome project is to completely analyze the human DNA sequence and furthermore shed light on the mysteries of the human body. Along the way, scientists completed the genomes of several other organisms including yeast and the fruit fly. In 2000, which is only ten years after the beginning of the project, the scientists announced that a "working copy of the human genome was essentially complete".
    The process by which the scientists confirmed the human genome is very intriguing. The scientists first determined the "markers", a characteristic sequence of bases that appears within the widely seperated regions of DNA, to locate and return to specific locations in the genome. Scientists then shredded the DNA into small pieces and determineed the sequence of bases in each fragment. The fragments are thoroughly analyzed by the computer and put together in accordance with the overlapping "markers" on the chromosomes--like a jigsaw puzzle put together.







                Works Cited

-Wikipedia, s.v. Human Genome Project
- Miller, Kenneth & Levine, Joseph. Biology, Prentice Hall, Boston ,MA
 

Lethal Genes-I don't wanna die!

     I need to admit that tragedies can often be very interesting. Lethal Genes, tragic as its name suggests, are genes whose phenotypes lead an organism to unconditional death. Death can sometimes not be immediate and take years or even decades. The notion that carriers of lethal genes cannot leave offspring is therefore false; for instance, the notorious Huntington's disease, inherited as an autosomal dominant condition, usually manifests itself when the patient ages over 40, enabling itself to clandestinely pass down to the patient's descents.
     Lethal genes were first discovered by Lucien Cuenot, a French biologist. Cuenot observed unusual genetic patterns while studying inheritnce of a coat color gene in mice. The offsprings of two yellow mice, quite surprisingly, always showed a 2:1 ratio instead of a conventional Mendelian 3:1. The mice happened to never produced a single homozygous yellow mouse. Five years later, W.E. Castle and C.C. Little confirmed the existence of lethal gene by showing that one-quarter of the offspring from crosses between heterozygotes die during embyonic development.

(Image Source: http://www.nature.com/scitable/topicpage/mendelian-ratios-and-lethal-genes-557)


     When an allele causes lethality, this is evidence that the gene must have a critical function in an organism. The discoveries of many lethal alleles have provided information on the functions of genes during development. Additionally, scientists can use conditional and synthetic lethal alleles to study the physiological functions and relationships of genes under specific conditions.