1. Figure DNA sequencers
DNA Technology

2. DNA Cloning
A molecular biologist studying a particular gene faces a challenge. Characteristics of a naturally occurring DNA molecule include:
Very long molecule
Carries many genes
Genes occupy only a small portion of the chromosome
A specific gene probably only makes up 1/1000,000 of the DNA chromosomal molecule
Subtle differences distinguish the gene from the surrounding material

3. To work with a specific gene, scientists need methods for preparing well-defined, gene-sized pieces of DNA in multiple identical copies.
They need techniques for GENE CLONING!
Most techniques for gene cloning share several general features – the use of bacteria and plasmids.

4. Vocabulary Review plasmid Recombinant DNA Genetic engineering
Small circular DNA that replicates within bacterial cells
plasmid
Recombinant DNA
DNA with genes from two different sources ( often different species)
Genetic engineering
Direct manipulation of genes for practical purposes
Restriction enzymes
Enzymes that cut foreign DNA
Restriction sites
Specific DNA sequence recognized by a restriction enzyme

5. Figure 20.1 An overview of how bacterial plasmids are used to clone genes

6. Using a restriction enzyme and DNA ligase to make recombinant DNA

7. Genes can be Cloned in Recombinant DNA Vectors
The plasmid is the vector. A vector is a means of transportation. It will carry the foreign DNA and will enter another cell and replicate. Bacterial plasmids are widely used as cloning vectors.
Bacteria are most commonly the host cell.
Ease of isolation
Ease of reintroduction
Replicate quickly

8. Procedure for Cloning a Eukaryotic Gene in a Bacterial Plasmid
Isolation of vector and gene-source DNA
Insertion of DNA into vector
Introduce cloning vector into cells
Cloning of cells with foreign DNA
Identification of cell clones carrying the gene of interest

9. Figure 20.3 Cloning a human gene in a bacterial plasmid: a closer look (Layer 1)

10. Figure 20.3 Cloning a human gene in a bacterial plasmid: a closer look (Layer 2)

11. Figure 20.3 Cloning a human gene in a bacterial plasmid: a closer look (Layer 3)

12. Figure 20.4 Using a nucleic acid probe to identify a cloned gene
If the cells containing a desired gene translate the gene into protein, then it is possible to identify them by screening for the protein. This if often done by using antibodies that bind to the protein.

13. Figure 20.5 Making complementary DNA (cDNA) for a eukaryotic gene

14. Figure 20.6 Genomic libraries

15. Figure 20.7 The polymerase chain reaction (PCR)

16. Figure 20.8 Gel electrophoresis of macromolecules