Beijing weather pollution index

The purpose of (1) experiment is to explore the effect of cigarette brine extract on the weight of rats. The experimental design should follow the control principle and the univariate principle. The single variable is the concentration of cigarette saline extract, while the control group needs to give the same amount of saline every day. As can be seen from the figure, the average weight of mice in the control group is the heaviest, and the greater the concentration of cigarette brine extract, the smaller the average weight of mice. It shows that the cigarette brine extract has obvious inhibitory effect on the body weight of rats, and the higher the dose, the stronger the inhibitory effect.

(2) One of the characteristics of cancer cells is that the morphological structure of cancer cells has changed, so it can be preliminarily judged whether canceration occurs by observing the cell morphology. The basic cause of canceration is gene mutation of proto-oncogene and tumor suppressor gene.

(3) The core step of genetic engineering is the construction of gene expression vector. First of all, it is necessary to cut the foreign DNA molecule containing the target gene and the plasmid (vector) with the same restriction endonuclease to form the same sticky end. Then DNA ligase was used to connect the target gene with the vector to form the recombinant plasmid.

(4) (2) is the process of cell subculture. Before this process, the cells attached to the culture dish wall should be treated with trypsin to form single cells and then subcultured.

(5) The most important feature of cancer cells is that they can proliferate indefinitely. As long as the proliferation of cancer cells can be inhibited, cancer can be treated. It can be seen from the figure that the mRNA transcribed by the let-7 gene can specifically bind to the mRNA transcribed by the RAS gene, thereby inhibiting the synthesis of the RAS protein, thereby inhibiting the proliferation of cancer cells and achieving the purpose of treating cancer.

So, the answer: material i.

(1) normal saline (2 points); Cigarette physiological saline extract has obvious inhibitory effect on the weight of rats, and the higher the dose, the stronger the inhibitory effect (2 points).

(2) Cell morphology (2 points); Gene mutation of protooncogene (or gene mutation of protooncogene and tumor suppressor gene) (2 points).

Materials 1 and 2

(3) homologous restriction endonuclease (homologous restriction endonuclease) (2 points); Plasmids (or vectors) and DNA fragments containing let-7 gene ((2 points), no score if one item is missing).

(4) Trypsin (2 points). (5) and RAS? MRNA specific binding inhibits the synthesis of RAS protein (2 points).