Bacterial artificial chromosome (BAC)

Definition

A bacterial artificial chromosome (BAC) is a cloning vector that can carry large fragments of DNA, typically between 100 to 300 kilobases, making it extremely useful for genomic mapping and sequencing. BACs are derived from the F plasmid of E. coli and are designed to replicate within bacterial cells, allowing researchers to maintain and propagate large segments of DNA in a stable manner. This capability makes BACs vital tools in molecular cloning techniques for studying complex genomes.

5 Must Know Facts For Your Next Test

1. BACs are particularly useful for cloning large DNA fragments due to their ability to accommodate inserts ranging from 100 to 300 kilobases, which is larger than many other vectors.
2. The use of BACs has been instrumental in sequencing large genomes, such as the human genome, allowing for the assembly of complex genomic sequences.
3. Each BAC contains a selectable marker, usually an antibiotic resistance gene, enabling the identification of successfully transformed bacteria that harbor the BAC.
4. BACs replicate within bacterial cells using the host's machinery, ensuring that the cloned DNA can be passed on through cell division without significant degradation.
5. The stability and size capacity of BACs make them preferred choices over other vectors when working with eukaryotic DNA or when constructing genomic libraries.

Review Questions

• How do bacterial artificial chromosomes differ from traditional plasmids in terms of DNA fragment capacity and application?
  • Bacterial artificial chromosomes differ from traditional plasmids primarily in their capacity to carry larger DNA fragments; BACs can accommodate inserts ranging from 100 to 300 kilobases, while typical plasmids usually carry smaller inserts of about 1 to 10 kilobases. This significant difference allows BACs to be more effective for genomic mapping and sequencing applications. As a result, BACs are often utilized in projects requiring the maintenance of larger genomic fragments, such as whole-genome sequencing initiatives.
• Discuss the role of BACs in the construction and utilization of genomic libraries.
  • BACs play a crucial role in constructing genomic libraries by providing a stable vector that can carry large inserts of DNA. When creating a genomic library, researchers isolate DNA from an organism and clone it into BAC vectors to maintain the integrity and viability of the genetic material. The ability of BACs to hold larger fragments facilitates the representation of complex genomes in their entirety, allowing for comprehensive analysis and identification of genes within the library.
• Evaluate the advantages and potential limitations of using BACs in molecular cloning compared to other vectors like cosmids or plasmids.
  • Using BACs in molecular cloning offers several advantages, including their capacity to carry larger DNA fragments and their stability within bacterial systems, which allows for easier manipulation and propagation. Unlike cosmids, which have a smaller insert size limit, or plasmids that typically accommodate even smaller inserts, BACs enable researchers to work with significant portions of eukaryotic genomes. However, potential limitations include the complexity and cost associated with handling larger constructs and the need for specialized techniques for efficient transformation into host bacteria. Understanding these trade-offs helps researchers choose the most appropriate vector for their specific cloning needs.

Related terms

Plasmid: A small, circular piece of DNA that can replicate independently of chromosomal DNA, commonly used as a vector for cloning in genetic engineering.

Genomic Library: A collection of cloned DNA fragments that represent the entire genome of an organism, allowing for the study and identification of genes.

Cosmid: A type of vector that is a hybrid between a plasmid and a bacteriophage, capable of carrying larger DNA fragments than typical plasmids, but smaller than BACs.