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Redefining Human: Part I Biology

by junnibug on Jul 11, 2010

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Environmental factors have affected the human body and human evolution. Here are 4 examples. Please read the notes for the full talk.

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Environmental factors have affected the human body and human evolution. Here are 4 examples. Please read the notes for the full talk.

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Welcome to part one of the two part talk entitled Redefining Human. My name is Jun, you can find me on twitter as @junnibug. My blog is evolvingoctopus.com. I will be talking about how environmental factors and other organisms have affected human evolution and the human body as we know it today. So, this talk will be very biologically focused, but the examples I will be giving should be rather familiar.
What does it mean to be human? Of course we are highly intelligent, we have a certain consciousness and awareness, we socialize and create culture. If you Google it, it says “a Homo sapian”. We are defined by physical characteristics, which then breaks into individual cells, and at the lowest level DNA. We often perceive ourselves as an entity. Although very complex, there is a sense of control from our DNA blueprint and we operate as a unit.
Of course, this is not true, there are tons of external factors that have altered our bodies and our DNA. I will be discussing four examples. First, the microorganisms that live in and on our bodies, also called human flora. Second I’ll be talking about viral DNA becoming a part of our “junk DNA”, which may or may not actually be junk. Third, I will talk about mitochondria and endosymbiotic theory. And last, I will talk about the text-book example of inheritance and selective pressures between sickle cell anemia and malaria.
Human flora is the encompassing term for all microorganisms living symbiotically in our bodies. There are various species of bacteria, fungi, and archaea that live in our gastrointestinal track, saliva, oral mucosa, and even on the skin.
Some of these organisms help digestion, breaking down complex chemical compounds that our intestines can’t digest. Others are not so beneficial, such as bacteria that cause stomach ache and cavities.
And other are even worse, causing disease ranging from mild to deadly. It’s not surprising we would be infested with bacteria, they are small and can live in a huge variety of environments. Because of their small size, it is estimated that our bodies are made up of ten times more microorganisms than our own cells. Another interesting fact is that babies are not born with any of these microorganisms but very rapidly acquire them from the environment, first of which is from mother’s milk. So these bacteria that have co-evolved with mankind are very much a part of our bodies. It’s not only living species that affect us, non-living entities, like prion proteins that cause mad cow disease and viruses like the swine flu have affected bodies too.
Which leads me to the second example: viral DNA. It is incredible that of our 3 billion base pairs of DNA, only 2 % of them encode for all the complex proteins in our body. But what’s even more amazing is the complexity in our 98 % of “junk DNA”. Turns out very little is junk. Most are regulatory elements that control when and where a protein is made. That’s why our brain and muscle cells have the same DNA, but are totally different. There are microsatellite DNA which are repeats of some DNA caused by errors during replication of the genome. There are relics and pseudogenes, which were genes that somehow became non-functional. Then, there’s a class called transposons, also known as jumping genes.
So DNA is made into RNA, and then it is made into protein. And each process is done by other proteins. Well, there exists a protein called reverse transcriptase that can make RNA back into DNA. They are often found in retroviruses like HIV, where the method of infecting a host is to make viral RNA into DNA and insert it into the host DNA, causing the host to produce viral proteins. However, sometimes, the viral DNA goes to the wrong place and never gets made into protein. The DNA therefore just hangs out in the host genome and doesn’t do much.
Transposons are also known as jumping genes since they apparently jump from one location to another. One type of transposon is caused by incorrectly incorporated viral DNA, where a functional reverse transcriptase gets made from host DNA to RNA and to the active protein. The reverse transcriptase then turns the RNA that made it back into DNA and the DNA gets incorporated into another part of the host genome. So there’s a bit of self-replication going on here. These jumping genes are pretty much useless, but there has been rare occasions where new genes were made. Also, it can cause disease.
Truly junk DNA, ones that were created through mistakes and random mishaps, do serve some purpose. They generate diversity between individuals, which is how DNA fingerprinting works. Obviously you wouldn’t be looking for differences in functional genes because if was a difference, you could be dead. These areas provide spacing between areas of important DNA for all kinds of molecules to bind. And lastly, junk DNA is simply there because there is no selective pressure to get rid of it. That’s just evolution, it’s not perfect.
The third example is mitochondria. These are the little factories in the cell that break down food into energy. They control cell cycle, growth, and aging. They more similar to bacteria than our own cells in regards to genome (which they have their own DNA), membrane, and method of replication. Unlike all other genes, mitochondria genes are inherited maternally only. Why are mitochondria so different?
It is believed that the first eukaryotes (or multi-cell organisms) became that way by single-celled organisms swallowing other single-celled organisms. This is called the endosymbiotic theory. Earlier, I was talking about how microorganisms are a part of us… well mitochondria microorganisms are REALLY a part of us from way back in evolution.
The examples I’ve been were about parasites (living and nonliving, as in the case of viruses) altering our bodies and genetics. My last example is about selfish genes and how selective pressures have orchestrated the fate of a single gene. Sickle cell anemia is a genetic disorder highly prevalent in Sub-Saharan Africa. It is caused by a single point mutation that cause red blood cells to have a sickle or half-moon shape. Normal blood cells are circular disks that can easily slide across each other. Sickle cells, however, clump up and can easily clog blood vesicles, which can be fatal. But this disease is extremely prevalent. Turns out carriers of this disease (who do not have the disease themselves) are resistant to malaria, another prevalent disease in the area caused by a parasite and carried by mosquitos. If you would recall punnett squares from genetics classes, sickle cell is a recessive disorder (so you would have the disorder if you have two small a’s, but would be fine if you had one big A). If two carriers mate, there is a 25 % chance of the child getting sickle cell, 25% chance of the child dying of malaria, but 50% chance that they won’t get both. So there is a selective pressure to be a carrier of sickle cell anemia, causing the disease to be more prevalent than it would have been otherwise.
So there you have it, 4 examples of how environmental factors have affected our genetics and evolution. There’s the microorganisms that live all over us, the mitochondria that was a bacteria that became a part of our cells, viral DNA jumping around genomes, and selfish genes that propagates at the expense of us.
So the redefinition of human is that we are a network of organisms and genetic factors. Lastly, a plug for Ignite San Diego coming August 3 rd . We’ll have a night of exciting talks and free beer. I’m one of the organizers, so hit me up if you want to know more about it.

Redefining Human: Part I Biology — Presentation Transcript

http://news.bbc.co.uk/hi/english/static/in_depth/sci_tech/2000/human_genome/
http://news.bbc.co.uk/hi/english/static/in_depth/sci_tech/2000/human_genome/ Human Flora Mitochondria Sickle cell vs Malaria Viral DNA
http://scienceblogs.com/clock/
http://giantmicrobes.com/ E. coli Yogurt (Lactobacillus bulgaricus) The Good The Bad Cavity (Streptococcus mutans) Stomach Ache (Shigella)
http://giantmicrobes.com/ The Ugly Swine Flu (Influenza A virus H1N1) Mad Cow (Bovine Spongiform Encephalopathy) Sore Throat (Streptococcus) The Plague (Yersinia pestis)
http://stevemorse.org/genetealogy/ 2 % 98 % Gene Regulatory Elements Microsatellite DNA Relics/Pseudogenes Transposons
http://stevemorse.org/genetealogy/
http://www.bio.miami.edu/~cmallery/
http://rps.psu.edu/probing/
- Generates diversity
- Spacer for DNA binding molecules
- No selective pressures
http://nsf.gov/news/overviews/biology/ Energy factory of the cell Control cell cycle, growth, and aging Bacteria-like genome, membrane, and replication Inherited maternally only
http://biology.iupui.edu/biocourses/N100/ Endosymbiotic Theory
http://giantmicrobes.com/, http://mun.ca/biology/desmid/brian/BIOL2250/, http://croptechnology.unl.edu/ Red Blood Cell Malaria
http://news.bbc.co.uk/hi/english/static/in_depth/sci_tech/2000/human_genome/ Human Flora Mitochondria Sickle cell vs Malaria Viral DNA
By Emma Hack, emmahackartist.com, pic via funnyartpictures.com

Redefining Human: Part I Biology

by junnibug on Jul 11, 2010

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Redefining Human: Part I Biology — Presentation Transcript