FoS II · Midterm 2

Lecture 12 — Recombinant DNA, gain of function, biosafety

The shared genetic code is what makes this whole field possible: DNA is read the same way in bacteria, plants and humans, so a human gene placed in bacteria can be transcribed and translated into a working human protein. That is why insulin can be made in E. coli.

DNA → RNA → protein → trait

  • DNA is transcribed into RNA; mRNA is translated into protein; proteins do the work that produces traits.
  • Move the gene, and you can move the trait, provided the host cell can read and process it.

The recombinant DNA toolkit

ToolWhat it doesThink of it as
Restriction enzymeCuts DNA at a specific recognition sequence, often leaving matching "sticky ends"Scissors that always cut at the same phrase
DNA ligaseJoins DNA fragments by sealing the sugar-phosphate backboneGlue or tape
PlasmidA small, usually circular DNA molecule that replicates in bacteria and carries the inserted geneA delivery envelope
Host cellTakes up the recombinant plasmid, copies it, and expresses the geneThe factory

The classic workflow: cut the gene of interest and the plasmid with the same restriction enzyme → mix so the matching ends pair → seal with ligase → insert the plasmid into a host cell → the host copies itself and makes the protein.

Recombinant DNA workflow Four steps. Cut: a restriction enzyme cuts the gene and the plasmid at the same sequence, leaving sticky ends. Join: DNA ligase seals the gene into the plasmid, making a recombinant plasmid. Insert: the plasmid carries the gene into a host cell. Express: the host cell copies the plasmid and makes the protein, for example insulin. plasmid, opened gene 1 · Cut Restriction enzyme cuts gene and plasmid at the same sequence: sticky ends recombinant plasmid 2 · Join DNA ligase seals the backbone, joining the gene into the plasmid host cell (bacterium) 3 · Insert Plasmid carries the gene into the host cell protein, e.g. insulin 4 · Express Host cell copies the plasmid and makes the protein from the gene
Each tool has one job. The restriction enzyme cuts, ligase joins, the plasmid carries and the host cell expresses. It works because every organism reads the genetic code the same way.

Recombinant DNA vs CRISPR

Recombinant DNACRISPR
Core actionJoins DNA from different sources and adds it to a hostTargets and cuts a chosen sequence in the genome
TargetingRestriction sites; insertion point often not controlledGuide RNA matches a specific sequence
Typical useMake a protein in bacteria; create transgenic organismsEdit, disable or correct a gene in place
ResultNew DNA addedExisting DNA changed

Both are genetic engineering; both are used in research and biotech.

Gain of function: the distinction that matters

  • Genetic engineering is a method — something a researcher does.
  • Gain of function is an outcome — a measured increase or acquisition of a biological activity. Loss of function is the reverse.
  • These are independent. Function can change through natural mutation with no engineering at all, and engineering can produce no functional change.

Gain of function does not mean "more dangerous." A bacterium that gains the ability to glow, to digest a new sugar, or to grow at a different temperature has gained function with no added hazard. The concerning subset is gain of function in a pathogen affecting transmissibility (how easily it spreads) or virulence (how much harm it causes), which is what the biosecurity debate is actually about.

Why a sequence alone proves nothing: knowing an organism carries an inserted gene does not tell you what it can do. Predicting function from sequence is unreliable; traits emerge from the whole organism in a context. A credible claim about changed function needs:

  • A comparison between the modified organism and the unmodified one.
  • Direct experimental measurement of the activity in question.
  • Appropriate controls, so the difference can be attributed to the change and not to handling, dose or conditions.
  • Repetition, because a single measurement can be noise.

This is the Jacobsen reading's relevance. It is a scenario, built from interviews and history, about what an engineered pathogen could do and how badly institutions might cope. Treat it as a tool for thinking about risk and oversight, not as evidence about any real organism. The same lecture's history (Asilomar, where scientists met to set rules for the new recombinant DNA work) is about how a field decided to govern itself.

Genetic engineering, gain of function and danger Two overlapping circles. Left: genetic engineering, a method. Right: gain of function, a measured outcome. Engineering with no change in function sits in the left circle only. A bacterium engineered to glow, or to tolerate salt, sits in the overlap. A natural mutation that gains a function sits in the right circle only. A small region inside gain of function marks increased danger: greater transmissibility or virulence in a pathogen. Genetic engineering a method Gain of function a measured outcome engineered, no change in function engineered to glow engineered salt tolerance natural mutation gains a function more danger More danger = greater transmissibility or virulence in a pathogen, a small subset
A method, an outcome, and a small subset. Engineering and gain of function overlap but neither requires the other. Increased danger (greater transmissibility or virulence in a pathogen) is only a small part of gain of function.

Biosafety levels

BSL is chosen from three things together: how hazardous the agent is, how it could get into a person (exposure route, especially whether it spreads through the air), and what you are doing with it. The same organism can require different handling for different procedures, because an activity that creates aerosols raises the risk.

LevelAgentsPractices and containment
BSL-1Not known to cause disease in healthy adults (common lab E. coli strains)Standard microbiological practice, open bench, sink, PPE such as gloves and a coat
BSL-2Agents associated with human disease, usually spread by ingestion or contact rather than air (Salmonella, hepatitis B, seasonal flu)BSL-1 plus restricted access, biosafety cabinet for aerosol-generating work, autoclave
BSL-3Agents causing serious or lethal disease, especially inhalable ones (tuberculosis)Controlled access, directional inward airflow, exhaust not recirculated, respiratory protection, all work in containment devices
BSL-4Exceptionally hazardous agents, often airborne with no vaccine or treatment (Ebola, Marburg)Full-body positive-pressure suit or Class III cabinet, dedicated isolated building, airlocks, chemical shower, all air and waste decontaminated

Containment covers the equipment, procedures and facility design that keep the agent away from people and the environment.

Biosafety levels 1 to 4 A ladder from BSL-1 at the bottom to BSL-4 at the top, rising with agent hazard and airborne risk. BSL-1: no disease in healthy adults; open bench, sink, gloves and coat. BSL-2 adds restricted access, a biosafety cabinet for aerosol work and an autoclave. BSL-3, for serious inhalable agents, adds controlled access, inward airflow, non-recirculated exhaust, respirators and all work in containment devices. BSL-4, for exceptionally hazardous airborne agents with no vaccine or treatment, adds a positive-pressure suit or Class III cabinet, an isolated building, airlocks, a chemical shower and decontamination of all air and waste. Containment layers accumulate at each level. agent hazard + airborne risk → BSL-4 Exceptionally hazardous, often airborne, no vaccine or treatment (Ebola, Marburg) Adds: positive-pressure suit or Class III cabinet, isolated building, airlocks, chemical shower, all air and waste cleaned BSL-3 Serious or lethal disease, especially inhalable agents (tuberculosis) Adds: controlled access, inward airflow, exhaust not recirculated, respirators, all work in containment devices BSL-2 Human disease, usually spread by ingestion or contact, not air (Salmonella, hepatitis B) Adds: restricted access, biosafety cabinet for aerosol-generating work, autoclave BSL-1 Not known to cause disease in healthy adults (common lab E. coli strains) Base: standard practice, open bench, sink, gloves and a coat
Containment accumulates as hazard rises. Each level keeps everything below it and adds barriers, with inhalable agents marking the jump to BSL-3. The activity matters too: aerosol-generating work raises the requirement for the same organism.

Check yourself

  • Write the recombinant insulin workflow from memory, naming each tool's job.
  • Give an example of gain of function that reduces danger.
  • Why might the same bacterium be handled at BSL-2 for one procedure and BSL-3 for another?
  • A paper claims an engineered virus is "more transmissible." What evidence would you need to see?

Further reading

Outside sources, opening in a new tab. The exam is on the course material; use these to check your understanding, not to learn new facts.

Tip: the ← and → arrow keys move between sections.