Understanding and Manipulating DNA
Uses of DNA
- DNA profiling (genetic fingerprinting)
- Genomic sequencing and comparative genome mapping
- Genetic engineering
- Gene therapy
All DNA contains sections called genes, which code for polypeptides and protiens. Coding DNA only forma 1.5% of DNA in humans. Much DNA is non-coding, formerly known as junk, but is now known to have regulatory functions.
Genomics - the study of genomes - wants to map the whole genome of organisms; comparing genes and DNA sequences to understand the relationship between genes and health, behaviour and evolutionary roles between organisms.
Sequencing Genomes - the basics.
The sequencing reaction can only operate on a length of DNA of around 750 base pairs. The genome must be broken up and sequenced in sections.
- Genomes are mapped to identify where on the chromasome they have come from; information that is already known is used (eg using microsatellites).
- Samples of the genome are sheared (mechanically broken) into sections of around 100,000 base pairs. Sometimes known as the "shotgun" approach.
- The sections are then placed into seperate Bacterial Artificial Chromosomes (BACs) and transferred to E. coli cells.
- This produces many copies of the sections, forming clone libraries.
Sequencing BAC Sections
In order to sequence BACs:
- cells containing specific BACs are cultured. DNA is extracted and restriction enzymes are used to cut it into smalled fragments.
- Fragments are separated using electrophoresis.
- Each fragment is processed using an automated process.
- Computer programmes compare overlapping regions from the cuts made by different restriction enzymes in order to reassemble the whole sequence.