Bacterial Transformation:

S-strain

Smooth strain of bacteria with a protective capsule, considered virulent (harmful).

R-strain

Rough strain of bacteria that lacks a capsule, considered non-virulent.

Heat-killed S-strain

S-strain bacteria that have been heated to kill them, used in Griffith's experiment.

Transforming principle

The ability of the dead S-strain DNA to transform the non-virulent R-strain into a virulent strain.

Desoxyribonucleic acid (DNA)

The molecule identified by Avery, Macleod, and McCarty as the transforming principle from Griffith's experiment.

Competent E. coli

E. coli bacteria made able to take up DNA from their environment under certain conditions.

Plasmids

Small circles of DNA that can carry genes, such as those for antibiotic resistance.

Antibiotic resistance gene

A gene carried by plasmids that allows bacteria to survive in environments containing antibiotics.

Why is the S-strain considered virulent while the R-strain is non-virulent?

The S-strain’s capsule protects it from the host’s immune system, making it capable of causing disease

What happened when mice were injected with a combination of the heat-killed-S-strain and live R-strain?

The mice lived. The S-strain was dead, so it could not reproduce or cause disease

What is the transforming principle?

It is the material that transferred genetic information from one strain to another, changing its characteristics

Which scientists later identified DNA as the transforming principle?

Avery, Macleod, and McCarty

What happens if a bacterium loses the plasmid it has taken in?

It will also lose any traits the plasmid gave it (like antibiotic resistance)

How can we tell if the transformation was successful in the lab?

Bacteria survive and grow on plates with antibiotics (because they took in the resistance gene)

Why is it important to include a control group in transformation experiments?

To show that only the transformed cells survive, proving the plasmid caused the resistance