Final Exam and Answers 2010 06

(1) What can P-53 gene do and why is it so closely related to many types of cancers?

P-53 gene produce P-53 protein that can : (1) suppress overly active, uncontrolled, cell division, (2) repair damaged DNA (UV or peroxide), (3) invoke cell suicide if DNA is too seriously damage. If P-53 gene is deficient, the above function can not performed, then the cancer suppression mechanism will not performed, therefore many types of cancers are easily occurred.

(2) Roughly explain how novelty-seeking personality could have a genetic origin.

Take dopamine type-4 receptor as example. Neural signal pass from one cell to another by releasing and accepting special kinds of molecules (in this case dopamine). A receptor on neuron (nerve cell) membrane is a protein, its structure will change after capture a signal molecule, revealing specific molecular segment that was originally covered This specific molecular fragment of protein serve as key-lock matching signal to be identify (through contact) by another type of protein to carry on the messaging passing to the nucleus of cell and clam the neuron down, which was how message is transfer into cell in this particular case. The DNA code of these receptors, there region that have certain repeated sequence, and the times of repetition is different from one to other. longer sequence gene produce receptors with longer poly-peptide (amino acid) chain (fragment) and tend to block the key-lock signal so making it harder to be identified, thus reduce the overall effect of calming cell down and thus brain remain excited. This is a reported theory that novelty-seeking personality could have a genetic origin.

(3) Explain the function of Telomere and its effect on how many times a cell can divide.

Telomere is a special repeating sequence that keeps each end of DNA stands sticking together. When DNA polymerase copy/reproduce DNA, it needs to attached onto one strand, therefore the attached "food-print" region is not duplicated. This means the newly reproduced DNA is always shorter than DNA by missing one section in their telomere region. Each time cell divide and DNA need to be duplicated, and telomere therefore become shorter. When telomere ending part of chromosome (DNA) finally disappear, DNA mess up in a disorder way and the cell will die (suicide). This explain (usual) cell has finite number of time to divide.

(Cancer cell and sex cells, for obvious reason, are two exceptions. Telomerase elongate the length of telomere making them not restricted by the usual constraint.)

(4) What is PCR (Polymerase Chain Reaction) that has to be used in DNA finger-printing.

PCR is a procedure to magnify tiny trace of DNA sections into a huge amount. PCR is carried out in cycles, in each cycle, DNA is heated up so that two complementary stands are separated, expose (nucleotides) ATCG base pairs allowing DNA Polymerase (a kind of enzyme that can duplicate DNA) to build-complete the double helix structure for each separated strand, thus double the number of DNA sections. For every single PRC cycle, number of DNA sections is doubled this way. Wait for long enough time, there will be sufficient amount of DNA sections that are identical to the trace amount sampled, say, from a crime scene.

(5) Genetically modified tomato have much longer shelf life, how was that possible?

Tomato skin cell will release a special kind of enzyme to decompose its cell wall after the fruit is mature enough, this timing come from evolutionally adapting environment to have a optimal effect to spread it seeds. The enzyme has it own gene, the technique to prolong the shelf life is to let tomato to have extra section of DNA (gene) to produce anti-sense RNA, in which the A,T,C,G base unnits are all complemantry to the original one. when when fruit mature, the RNA of cell wall decomposing enzyme is combined and blocked by its anti-sense RNA. The synthesis of the enzyme is therefore suppressed and the process of cell wall decomposition takes much longer time to happen. As for how are genetic engineered anti-sense gene was inserted into tomato, it is carried by virus infection.

(6) The latest theory predicted modern human come from Africa, by analysing ring-like DNA in mitochondria (single : mitochondrion). How was such reasoning established?

Mitochondria DNA is ring like and only come from mother, it therefore is very slow to change following on the natural rate of mutation to occur. Examining the diversity of mitochondria DNA from a population, scientists can predict how close two sub-race are related and also workout the chronological order of a given population in a give area. It is in this way current theory suggest the existing human population in the world has a common ancestor from Africa.

(Other archeologically discovered early human-like races such as Neanderthal man and Pek-king man are not the direct ancestor of modern mankind.)

(7) Sub atomic particles can appear in anywhere at same time, which scientific revolution help mankind to understand this?

Quantum revolution.

(8) What are carbon nanotubes?

Carbon nanotubes are very small tube-like objects made of layer or layers of carbon atoms linked (by chemical bonding) in regular hexagonal (triangular) repeated manner.

(9) Nuclear fusion provide clean and almost unlimited energy source compared to the scale that human use today, what is the major problem need to be overcome ?

Sustaining the condition of fusion reaction (currently only 30 seconds achived) is the major challenge.

(10) What is the ratio of genetic overlap between human and mice ? and how about chimpanzee ?

Mice : 75% ; chimpanzee : 98.4%.