Chapter 13: DNA, RNA, and Proteins

[Pages:83]Chapter 13: DNA, RNA, and Proteins

Lecture Notes

13.1 THE STRUCTURE OF DNA

EQ: HOW DOES THE STRUCTURE OF DNA RELATE TO ITS FUNCTION?

? Known since the late 1800s:

1.Heritable information is carried in discrete units called genes

2.Genes are parts of structures called chromosomes

3.Chromosomes are made of deoxyribonucleic acid (DNA) and protein

? KEY CONCEPT: DNA was identified as the genetic material through a series of experiments.

? Transformed bacteria revealed the link between genes and DNA

? F. Griffith worked with two strains of Streptococcus pneumoniae bacteria

? S strain caused pneumonia when injected into mice, killing them

? R strain did not cause pneumonia when injected

Griffith Transformation Experiment

Mouse injected w/bacteria Results

Conclusions

R strain does not cause pneumonia

S strain does cause pneumonia

Heat-killed S strain does not cause pneumonia

Substance from heatkilled S strain can transform harmless R strain into deadly S strain

Genes Are Made of DNA

? Deductions from Griffith's experiment (1920s)

? Living safe bacteria (R strain) were changed by something in the dead (but normally disease-causing) S strain

? The living R strain bacteria were transformed by genetic material released by the S strain

? Later findings by Avery, MacLeod, and McCarty (1940s)

? The transforming molecule from the S strain was DNA

Avery's Experiments

? Avery identified DNA as the transforming principle.

? Avery isolated and purified Griffith's transforming principle.

? Avery performed three tests on the transforming principle.

? Qualitative tests showed DNA was present. ? Chemical tests showed the chemical makeup matched

that of DNA. ? Enzyme tests showed only DNA-degrading enzymes

stopped transformation.

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