What is the main goal of studying gene isolation and DNA sequencing in this module?
To learn how genes are isolated, DNA is sequenced (plasmid-level and whole genome), and how DNA sequences are interpreted.
What major project was announced in 1993 and considered ambitious?
The Human Genome Project.
What is the 1KSA project?
A project aiming to sequence 1000 South African plant and animal genomes.
Name four key molecular tools that revolutionized biotechnology
Restriction enzymes, DNA ligases, DNA polymerases, and PCR.
How does PCR amplify a gene in vitro?
By repeated cycles of DNA denaturation, primer annealing, and extension by DNA polymerase
How does in vivo amplification of a gene work?
A gene is cloned into a vector, introduced into bacteria, and replicated as bacteria grow, producing many copies.
What are the main challenges in cloning a gene of interest?
- Cutting the DNA and inserting it into a vector
- Introducing the vector into bacteria
- Maintaining selection for bacteria with the vector
- Producing many copies of the gene
How are these challenges solved?
- Restriction enzymes & ligases cut and join DNA
- Transformation & selection introduce vectors into bacteria
- Plasmid origin of replication ensures vector replication
What are restriction enzymes?
Enzymes that cut DNA at specific sequences; originally discovered as a bacterial defense against viruses.
How do bacteria protect their own DNA from restriction enzymes?
By methylating specific sequences (-CH₃ groups), preventing enzyme cutting
Who discovered restriction enzymes and who applied them to genetics?
Werner Arber discovered them; Hamilton O. Smith verified; Daniel Nathans applied them to genetics.
What are the types of cuts restriction enzymes can make?
- 5’ overhangs
- 3’ overhangs
- Blunt ends
How do you estimate how often a restriction enzyme will cut a genome?
Using the formula 4ⁿ, where n = length of recognition site in bp.
How often does RsaI (4bp cutter) cut the human genome (~3 Gb)?
3 × 10⁹ ÷ 4⁴ ≈ 11.7 million times.
Why is the choice of restriction enzyme important in cloning?
Because it determines fragment size and compatibility for ligation into vectors.
What is a plasmid origin of replication and why is it important?
A DNA sequence that allows the plasmid to replicate independently in bacteria, producing many copies of the gene.
What is transformation in molecular biology?
The process of introducing a plasmid into bacteria so that they can carry and replicate it.
What is the function of antibiotic selection in cloning?
To ensure that only bacteria containing the plasmid survive, maintaining the desired clones.
Who received the Nobel Prize for the discovery and application of restriction enzymes?
Werner Arber, Hamilton O. Smith, and Daniel Nathans.
What determines whether a restriction enzyme will cut frequently or rarely?
The length of its recognition sequence (short sequences = more frequent cuts; long sequences = less frequent cuts).
Why is it important to know whether a restriction enzyme produces blunt or sticky ends?
Because compatible ends are needed for efficient ligation into a vector.
Two strategies for isolating a gene of interest?
A: 1. In vivo (bacterial cloning with plasmids)
2. In vitro (PCR amplification)
What are the main steps in PCR?
Denaturation → primer annealing → DNA extension, repeated in cycle
What is a vector in molecular cloning?
A DNA molecule (like a plasmid) used to carry a gene into a host organism for replication
