2.2 Applications and skills
2.2.7 The genetic code and enzymes in biotechnology
- Enzymes are used extensively in many different industries, for food production, forensic analysis and medicinal treatment.
- Bacteria and microorganisms are used to produce enzymes for human applications.
- These applications illustrate the universality of the genetic code.
Application: Production of lactose-free milk
- Lactase is the enzyme that digests lactose into glucose and galactose. This is a hydrolysis reaction that occurs in the small intestine.
Figure 2.2.7a – Hydrolysis of lactose into glucose and galactose
- All humans produce lactase as infants, but in some people the gene coding for lactase production becomes inactive. As adults, these people are lactose intolerant.
- Ingesting milk products causes cramping or diarrhea in people with lactose intolerance.
- Lactase is produced by mammals, but also by some bacteria and yeasts. Lactase extracted from microorganisms can be used to digest lactose in milk for human consumption, as shown in Figure 2.2.7b.
- Milk is poured through a column containing immobilised lactase (shown in alginate beads).
- In the column, the hydrolysis of lactose (into glucose and galactose) occurs.
- The result is lactose-free milk.
Application: Polymerase chain reaction (PCR)
Figure 2.2.7c – Role of taq polymerase in PCR
- During a polymerase chain reaction (PCR), a fragment of DNA is targeted and replicated in order to produce a larger sample.
- Inside the PCR chamber, DNA is heated to 95°C, the temperature needed to break hydrogen bonds between strands.
- Taq polymerase is a DNA polymerase enzyme produced naturally by a heat-tolerant bacterium, called Thermus aquaticus. It is used in PCR because it maintains its structure at high temperatures, while other DNA polymerases do not.
- After the strands are separated by heat, the chamber is then cooled to allow for DNA replication to occur on the template strands.
- With each heating and cooling cycle, the amount of DNA doubles as taq polymerase binds to each new template strand.
- The result is a sample of DNA that is large enough to analyse using other laboratory techniques, for example in crime scene investigations.
Application: Production of human insulin in bacteria
- Insulin is a hormone required for the delivery of sugar from circulating blood into cells.
- Diabetes is a disease caused by a deficiency in insulin function. It may be treated by daily injections of insulin.
- Different species produce a slightly different form of insulin, as determined by their amino acid sequence.
- In some animals, the differences are small. For example, insulin extracted from the pancreas of pigs and cows has been used in the past to treat diabetes in humans.
- Now biotechnologists are able to engineer bacteria to produce human insulin using recombinant DNA technology.
- By inserting human insulin genes into a bacterial plasmid, and allowing the bacteria to reproduce, entire colonies of bacteria now contain the human insulin gene.
- The bacteria use their own DNA to produce new copies of the human gene and their own ribosomes to translate new amino acids for the production of insulin.
- The resulting insulin is identical in structure to that produced by human pancreatic cells.
Figure 2.2.7e – Natural habitat of Thermus aquaticus
The genetic code is universal, so:
Figure 2.2.7f – Green glowing mice
A jellyfish bioluminescence gene expressed in mice
Technologies may benefit some human populations more than others. For example, lactose intolerance is more prevalent in Africa and Asia, whereas diabetes is more prevalent in Europe and North America.
Think about it!
How do the applications on this page illustrate the universality of the genetic code?