Question

Bacterial cells, such as E. coli, are surrounded by a fluid plasma membrane and enclosed by a rigid cell wall that protects the cell from damage. You will recall that there is no nuclear envelope in prokaryotic cells, but rather a “nucleoid region” with a single chromosome that is continuous (circular), not linear, as in eukaryotes. All of the genes required for basic survival and reproduction are found in the main chromosome. In addition to the main chromosomes, some DNA is found in a number of plasmids--small rings of DNA. Plasmids carry only a small number of genes for specialized functions, including resistance to specific drugs. The genetic code in bacteria is DNA composed of the same nucleotides as in eukaryotes, indicating the universality of the genetic code. Regardless of the source or species, all DNA has the same four nucleotides: adenine, thymine, cytosine, and guanine. For this reason, a eukaryotic gene--such as one for producing human insulin--can be inserted into a plasmid, and when taken up by a prokaryotic bacterium, can then be expressed by the bacterium. This process is called transformation, and occurs when a bacterium takes in foreign DNA and expresses the foreign gene. Transformation can occur naturally when a bacterium is exposed to foreign DNA, as described in the famous experiments of Frederick Griffith using mice exposed to pathogenic and non-pathogenic strains of Streptococcus pneumoniae. Cell wall: Plasma membrane Plasmid Bacterial chromosome In this investigation, E. coli cells are exposed to plasmids containing a gene for resistance to ampicillin. If the susceptible E. coli bacteria incorporate the foreign DNA, they will become ampicillin resistant. Which of the following statements are true? Select all that apply.

Answer 1

Transformation in bacteria is a procedure by which transfer of foreign DNA of a bacteria integrates into the chromosome of another bacteria. In this case, when a bacterial cell dies or disintegrates, the DNA is released into the surrounding environment. When a competent bacteria comes into contact with that piece of DNA, it uptakes the DNA. No protein uptake takes place via this method.

Bacterial plasmids are small circular piece of DNA which remain independently in a bacterial cell. The normal single circular chromosome of bacteria serves the common functions like transaction, whereas, plasmids have unique genes that serve specialized functions among which the main is ANTIBIOTIC RESISTANCE. Plasmids are a useful tool in genetic engineering. They can be engineered to carry the gene of interest to the target bacteria. To perform this method, plasmids are cut with restriction enzymes, gene of interest is then ligated and finally, the cuts are sealed.

Based on the above discussion, points that are true are listed below ----

transformation occurs when foreign genes are introduced into a host cell.

plasmids can be engineered to carry foreign DNA.