F215 module 2 Chapter 3 - Genomes and gene technologies
a. Outline the steps involved in sequencing the genome of an organism
- The genomes are mapped to find out which part of the genome they are from. This can be done by using the location of microsatellites which are short runs of repetitive sequences of 3-4 base pairs.
- Sample of the genome are mechanically broken to smaller sections of 100,000 base pairs- “Shotgun”approach.
- These sections are placed into separate bacterial artificial chromosomes (B.A.C’s) and then are transported to E.coli.
- These cells are then grown in culture so many clones of the sections are produced.
- The cell are then known as clone libraries.
b. Outline how gene sequencing allows for genome-wide comparisons between individuals and between species
- The identification of genes that code for proteins can be compared.
- Comparing genes of different species can show evolutionary relationships. This is because the more DNA sequences that they share, the closer related they are.
- Comparing genes for the same or similar proteins across a range of organisms is known as comparative gene mapping.
- You can model the effect of changes to genes, for example yeast.
- By comparing genomes from pathogenic and similar but non pathogenic organisms it can be used to identify the genes or base-pair sequences that are most important in causing a disease which can then lead to developing better drugs and medicines.
- By analysing the DNA of individuals it can reveal mutant alleles or alleles present that are associated with an increased risk of a particular disease.
c. Define the term recombinant DNA
- Recombinant DNA is a section of DNA often in a plasmid which is formed by joining DNA from two different sources.
d. Explain that genetic engineering involves the extraction of genes from one organisms and placing them in another.
- The required gene is obtained. The mRNA is produced from transcription and the gene is synthesised by automated polynucleotide sequencer. A DNA probe is used to locate the DNA fragments.
- Copy of the gene placed in a vector. It is sealed using DNA ligase and vectors are needed to contain regulatory sequences of DNA.
- The vector carries the gene to the recipient cell. This can be done via: electroporation, microinjection, viral transfer, liposomes.
- The recipient expresses the gene through protein synthesis.
e. Describe how sections of DNA containing a desired gene can be extracted from a donor organism using restriction enzymes
- Restriction enzymes cut through DNA at specific points.
- A particular restriction enzyme will cut where a specific base sequence occurs which is known as the restriction site and it is usually less than 10 base pairs.
- The enzyme catalyses a hydrolysis reaction to break the sugar phosphate backbones of the DNA double helix.
- Some bases are exposed known as a sticky end.
f. Outline how DNA fragments can be separated by size using electrophoresis
- DNA samples are cut with restriction enzymes.
- The DNA samples are placed into wells cut into the negative electrode end of the gel.