Summary of "Survival of the Sickest" Chapter 6

  The Chapter 6 of "Survival of the Sickest" starts off with the origin of vaccination. The vaccine came from the Latin word of "cowpox" which is an infection that can used against smallpox. Soon after, the author begins to talk about genes. The genes of a person are organized in 23 pairs of chromosomes, one set of 23 chromosomes came from the mother, and the other set came from the father. However, less than 3% of the DNA are about instructions of building cells, and scientists decided to call the other 97% the noncoding DNA instead of "junk DNA" because the fact that they are only not directly involved with creating proteins doesn't make the 97% useless. Also, the author noted an interesting fact that the mitochondria (the power plant of a cell) was once a bacteria that lived along with humans. 
  Later on, the author switches the topic to mutations. The genetic changes occur not only when there are errors in the transport of genetic data between generations, but also when organisms are exposed radiation or powerful chemicals. Outbreaks and pandemics are caused by either antegenic drift (when a mutation occurs in DNA of a virus), or antigenic shift (when a virus acquires new genes from a related strain).
  And finally, another topic the author mentioned was the "jumping gene". When the organisms are under extreme outside conditions, a sequence of DNA "copy and paste" themselves from one place to another, insert themselves into active genes and affect nearby genes by changing the entire sequence. This mutation is called "Jumping genes", and it was discovered by Barbara McClintock. There are two types of "jumping genes"- the first is DNA transposons, which jump through a cut-and-paste process; the second type is called DNA retrotransposons, which goes through a copy-and-paste process. Especially, the transposon is a huge part of our noncoding DNA, or "junk DNA".

- Andy Liu '15

13. Understanding DNA

  Today, to start off Unit 3, we learned about the structure and functions of DNA. DNA is the genetic material that transfers to a cell, and it is composed of nucleotides. Each nucleotide contains a nitrogen base, a 5-carbon sugar, and a phosphate group. 
  According to Chargaff's rule (discovered by Edwin Chargaff in 1947), he found out that the 4 types of bases are A (adenine), C (Cytosine), G (Guanine), and T (Thymine), and A=T, C=G. Also, Chargaff claimed that the composition of DNA is different between species, which add more evidence to prove that the DNA is the genetic material. 
  In early 1950s, Rosalin Franklin made a x-ray diffraction data on the structure of DNA. James D. Watson and Francis Crick indirectly obtained her data, and concluded that the structure of DNA is a double helix. The phosphate group and 5-carbon sugar are the backbones. The nitrogen bases became the "steps"  and they face toward the center of the helix. 
  The finding of Chargaff and the structure of DNA demonstrated the nature of base pair. Adenine always pairs with Thymine, and Cytosine always pairs with Guanine. This explains why the number of Adenine is always equal to that of Thymine, and the number of Cytosine is equal to that of Guanine. Adenine and Guanine are purines, which consist of two ring structures. Thymine and Cytosine are pyramidines which have one ring structures. By combining a purine structure with a pyramidine structure together, the distance between two sugar-phosphate backbones are always constant, thus maintaining a uniform structure. 

A summary of everything above... (just in case if you're bored)

  The activity we did today was to create a double-helical structure of DNA. We were given 4 pieces of paper with the drawing of 10 bases, scissors and tapes. We need to cut the paper in half, and cut along the edges of the nitrogen bases so that the bases can connect to each other, and become 5 base pairs with short pieces of tape attached. Later on, we taped all 4 pieces of paper together from the edges, and twisted the long piece of paper to create a helix shape. Finally we taped both ends of the paper. 

So this is what we got at the end... kindergarten style lol

  Finally we learned about the DNA replication. DNA replication occurs when the eukaryotic cell cycle is in the Synthesis phase. Both strands of the double helix can serve as the template for replication. 
  The process starts as an enzyme, DNA helicase, breaks the hydrogen bonds connecting the two parts of the parental strand and creates a replication fork. the final structure would be two branch strands (leading (5-Carbon) strand and lagging (3-carbon) strand) with exposed nitrogen bases, that allow themselves to be read by DNA polymerase. This enzyme is in charge of building complementary DNA strands. 

- Andy Liu '15

Answers for Article "From Atoms to Traits"

1.  Explain the significance of Mendel. 

  Mendel’s experiments on crossbreeding peas changed the general view in his period on heritable variations from ephemeral and random mixing to traits passed from one generation to another, even though the traits may not be visible.

2. Draw the structure of DNA and who discovered this structure. 

  James D. Watson and Francis Crick discovered the structure (drawing above)

3. Explain each of the five examples of variations that occur to DNA and give an example of each.

 1) Point Mutation: The substitution of a single base pair. 

Example: A slender silhouette and a hulking animal

 2) Insertion: The addition of extra base pairs in the sequence

Example: A smooth pea and a wrinkled pea

 3) Gene Copy Number: Difference in the number of duplication of an entire sequence
Example: the genes for starch digestion in chimpanzees and humans

 4) Duplication: Difference in the number of duplication of a base pair
Example: Signal receptor for pigment cells in pigs

 5) Regulatory changes: the change in the formation of gene sequences during the organism's development
Example: the difference in traits of the bushy teosinte and the tall modern cornstalk

4. What is evo-devo? 

  Evo-devo is the abbreviation of Evolutionary development biology. It is a field of biology that compares the developmental processes of different organism to determine the ancestral relationship between them, and to discover how the processes are influenced by evolutionary forces. 

5. Make a connection between human migration and the mutation of lactose intolerance.
  If a person comes from a population that stop consuming lactose products after infancy, and he goes to a region where the people consume lactose through adulthood, he will be lactose intolerant since his body lacks the mutant form of lactase enzyme that continues to be active in adulthood.