Lec 2-1

Question 1

What is the substance inside the cell nucleus

Johann Friedrich Miescher

Answer 1

Isolated nuclei from white blood cells

Found a substance in 1869 that is slightly acidic and high in phosphorous (nuclein)

Later renamed to nucleic acid and consisted of nucleic acid and proteins

Believed that proteins were the substance that carried hereditary info

Question 2

What is inside the cell nucleus

Albrecht Kossel

Phoebus Levene

Answer 2

Found 4 nitrogenous bases

Discovered DNA as a polymer-made up of repeating units of nucleotides

Question 3

Levene incorrect hypothesis

Answer 3

Proposed DNA consisted of a series of repeating, invariant, 4-nucleotide units in a fixed sequence: the tetranucleotide hypothesis

Question 4

Chargaff tests on the tetranucleotide hypothesis found

Answer 4

A = T

G=C

Thus disproving the tetranucleotide hypothesis

Question 5

Three experiments that proved DNA as carrier of genetic info

Answer 5

Griffith experiment (1928)- Discovery of the Transforming Principle in bacteria

Avery, Macleod, and McCarty’s experiment (1944)- Identification of the Transforming Principle in bacteria

Hershey-Chase experiment (1952) with viruses

Question 6

Discovery of the Transforming Principle in bacteria

Answer 6

Virulent and nonvirulent bacteria is injected into mice (virulent kills mouse)

Heat-killed virulent bacteria are injected into a mouse (mouse lives)

A mixture of the nonvirulent and heat-killed virulent are injected into a mouse (mouse is killed)

Proved that virulence can transform non-virulent bacteria, even when dead

Question 7

Identification of the transforming principle in bacteria

Answer 7

Asked what the chemical nature of the transforming principle is

Kill virulent bacteria with heat, homogenize, and filter

Treat samples with enzymes that destroy proteins, RNA, or DNA

Add the treated sampled to cultures of non-virulent bacteria

Cultures treated with protease or RNase contain transformed into virulent bacteria

Culture treated with DNase stayed non-virulent

Because DNase destroyed the transforming substance, the transforming substance is DNA

Question 8

Hershey and Chase Experiment with Viruses

Answer 8

T2 is a bacteriophage that infects E Coli

Phage Genome is DNA

All other parts of the bacteriophage are protein

Phage attaches to E.coli (bacteria) and injects its chromosomes

Bacteria chromosome breaks down and the phage chromosome replicates

Expression of phage genes produces phage structural components

Progeny phage particles assemble

Bacterial wall lyses (breaks), releasing progeny phages