it must be stable over time

it must be faithfully replicated

it must be informational content

it must on rare occasions be able to change (mutations)

genes reside on chromosomes

chromosome contain protein and DNA

Proteins

DNA (deoxyribonucleic acid)

the agent that causes pneumonia

Inject mice with virulent SP (type IIIS) —> mice dies, IIIS cells recovered from mice

Inject mice with nonvirulent SP (type IIR) —> mice survive, no bacteria recovered from mice

inject mice with heat-killed virulent IIIS —> mice survive, no bacteria recovered from mice

inject mice with heat-killed IIIS and live IIIR —> mice die, live type IIIS bacteria recovered from mice

prepare extracts of S cells and try to purify the transforming principle

their experiment suggest that DNA is the transforming principle:

They want to know whether the T2 genes are made of DNA or protein

Bacteriophages are viruses that infect bacteria (e.g., E. coli)

Mutant strains of bacteriophages can be isolated and stably propagated

E. coli phages such as T2 are composed of ~ 50% protein and ~ 50% DNA. The DNA is found in the head of the phage; all other viral structures are made of protein.

Phases T2 attaches E. coli and injects its chromosome

The bacterial chromosome breaks down —> phases chromosome replicates

Expression of phage genes produces phage structural components

The bacterial wall lyses —> releasing progeny phage