105-2 Final Exam Example Answers


(1) How was protein made in cells? Describe in detail.

In cell nucleus, by RNA polymerase : DNA -> mRNA

In cytoplasm (cell matrix), by ribosome : mRNA -> amino-acids on tRNA -> amino-acid chain -> folded into protein


(2) What is the most important experimental method help determined the structure of DNA as double helix?

X-ray diffraction.


(3) Explain PCR (Polymerase Chain Reaction).

PCR is a standard method of duplicate a section of DNA.

A DNA section is heated in a solution so its combined double starnd splits into two signe strand, DNA polymerase is then used to duplicate complementary starnd and form bouble starnd, after this repeat the heating again as next cycle. As one can see, each cycle will double the number of DNA strands. Keep performing this cycle (each cycle takes 20 min to complete), huge amount of identical DNA sections could be produced for later analysis.


(4) Rats and human has 75% gene in common, and chimpanzee has 98.4%, but man and apes are so different, how to rationalize this?

There are 25,000 genes in human genome, 1.6% accounts for roughly 400 gene difference, which is quite a lot, especially if here are key genes involve.


(5) Why the success of Human Genome Project depends on the powerful computers?

Very large number of identical copies of human DNA was cut at random positions (using enzymes) into many smaller pieces of DNA, making it easier to sequence. Computer is then used to reconstrct long secuence based on overlapping contents (say, one short sequence is 1234, another 3456, it is possible that the riginal sequence is 123456), this is why a powerful computer is needed.