Microorganisms: Applications in Molecular Biology


Microorganisms, most notably yeast and bacteria, are used in research and industry for cloning genes, replicating DNA and producing purified proteins. Yeast, in particular, is widely used as a model organism for studying a variety of cell functions.

Keywords: plasmids; vectors; tissue culture; cloning; genomes

Figure 1.

The E. coli lac operon. The lac operon contains three genes (lacZYA) whose products are needed for E. coli to utilize lactose as an energy source. These genes are regulated by operator (O) and promoter (P) sequences immediately adjacent to the genes. (a) When no lactose is present in the bacterial cell environment, repressor protein bound at the operator (O) prevents RNA polymerase from binding at the promoter (P). (b) When lactose is present, inducer (a lactose byproduct, represented as •) is produced, which can bind to the repressor. The repressor then no longer binds the operator, and the promoter is accessible to RNA polymerase.

Figure 2.

Ligating, transforming and selecting plasmid DNA. (a) Linearized vector is ligated to a fragment of foreign DNA, forming a circular plasmid. When this plasmid is transformed into bacteria, the ampicillin resistance gene is expressed, producing an enzyme that degrades ampicillin. (b) When the bacteria are plated on to media containing ampicillin, cells containing the plasmid (and thus ampicillin‐degrading enzyme) grow and form colonies (large, dark circles). Many of the cells do not contain the plasmid and fail to divide (represented as small, faint circles, although they would not be at all visible).

Figure 3.

Bacteriophage life cycle. The bacteriophage, a capsule of proteins (called a phage particle) surrounding the phage DNA, anchors on to the surface of the bacterial cell (1) and injects its DNA into the cell (2). Once inside the bacterial cell, the bacteriophage DNA is transcribed into RNA (3), and also replicated to produce many copies of the phage DNA (4). The RNA is translated by the bacterial ribosomes (5), so that numerous phage particles, containing phage DNA, can be assembled (6). The phages then signal lysis of the bacterial cells, releasing a multitude of new phages (7), which can then infect neighbouring bacteria.


Further Reading

Alberts B, Johnson A, Lewis J et al. (2002) Manipulating proteins, DNA, and RNA. In: Molecular Biology of the Cell, chap. 8. New York and London: Garland Science. [available on‐line at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books]

Lodish H, Berk A, Zipursky S et al. (2000) Chapter 6: Manipulating cells and viruses in culture and Chapter 7: Recombinant DNA and genomics. In: Molecular Cell Biology. New York: W. H. Freeman & Co. [available on‐line at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books]

National Center for Biotechnology Information. [http://www.ncbi.nlm.nih.gov/]

Saccharomyces Genome Database. [http://www.yeastgenome.org/]

Sherman F (1998) An Introduction to the Genetics and Molecular Biology of the Yeast Saccharomyces cerevisiae. [http://dbb.urmc.rochester.edu/labs/sherman_f/yeast/index.html]

Web Links

http://www.ncbi.nlm.nih.gov/ NCBI (National Center for Biotechnology Information) provides public assess to vast amounts of scientific information and tools, including scientific references, genomic and gene sequences, human genetic diseases, and nucleic acid and protein structures.

www.yeastgenome.org The Saccharomyces Genome Database is a comprehensive, public database that lists each yeast gene with extensive annotations to sequence data, protein data, cellular localization studies, known functions, published references, gene expression data (i.e. from DNA microarrays), and interactions with other genes.

http://sequence‐www.stanford.edu/group/yeast_deletion_project/deletions3.html The Saccharomyces Genome Deletion Project is a collaborative effort among many researchers studying yeast to create a library of yeast strains, each with a different gene deleted.

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How to Cite close
Keeney, Jill B(Dec 2007) Microorganisms: Applications in Molecular Biology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000971.pub2]