ORIGINAL QUESTION: Which molecule contains genetic information?

ORIGINAL QUESTION:

Which molecule contains genetic information?

ExperimentsFrederick Griffith (1928) - English

A. Smooth bacteria → mouse = dies of pneumonia

B. Rough bacteria → mouse = lives

C. Heat-killed smooth bacteria → mouse = lives

D. Heat-killed smooth bacteria + → mouse = dies of

pneumoniaLive rough bacteria

Fig. 12.2 p. 327

Fredrick Griffith

GriffithConclusion: Some molecules changed the harmless rough bacteria into deadly smooth bacteria → transformation!

Oswald Avery (1944) - CanadianQuestion: What molecule was needed for transformation?

Avery examined 4 macromolecules – destroying 1 at a time1. Lipids 3. Proteins2. Carbohydrates 4. Nucleic Acids

(DNA)

Oswald Avery

Transformation was blocked ONLY when DNA was destroyed Conclusion = Genes are made of DNA

Alfred Hershey & Martha Chase (1952) - American

Bacteriophage = a virus that infects bacteriaMade of protein and DNA

Question: Which enters a bacterium during infection?

They used “tracers” = radioactive isotopes1. phosphorus-32 → part of DNA (not proteins)2. sulfur-35 → part of proteins (not DNA)

Question: Which enters a bacterium during infection?

They used “tracers” = radioactive isotopes1. phosphorus-32 → part of DNA (not

proteins)

2. sulfur-35 → part of proteins (not DNA)

Fig. 12.3

Hershey & ChaseProcedure: A) Let bateriophages infect bacteria B) Analyzed bacteria for radioactivityC) Found phosphorus-32 sample made the

bacteria radioactive

Conclusion: Genetic material is DNA NOT protein

Martha Chase & Alfred Hershey

Nucleic acids = chain of nucleotides (polymer)

Nucleotides consist of : 1. 5-carbon sugar2. phosphate group3. nitrogenous base

DNA: deoxyribonucleic acid is a nucleic acid

Made of 4 different nucleotides:

1. adenine 3. guanine2. cytosine 4. thymine

Chargaff’s Rules - Erwin Chargaff (1950) - American

In samples of DNA:The amounts of adenine (A) and

thymine (T) were equalThe amounts of cytosine (C) and guanine (G) were equal

Chargaff’s Rule: C = G and T = A

Erwin Chargaff

Rosalind Franklin &Maurice Wilkins (1952) – British

Used X-Ray diffraction to analyze DNA molecules

These X-Ray patterns helped to solve the structure of DNA

Rosalind Franklin

Fig. 12.6

Maurice Wilkins

James Watson & Francis Crick (1953) – American & English

Solved the mystery!DNA is made of 2 strands twisted in a

“double helix”“Base pairs” are formed between

nitrogenous bases (A, T, C, G)Hydrogen bonds formed between A and

THydrogen bonds formed between C and G

Frances Crick

James Watson

Watson & CrickKind of like a twisted ladder!Rails of the ladder are strands of

alternating deoxyribose and phophateOne rail runs up, the other runs downThe steps or rungs are the

pairs of bases (C-G or T-A)

NucleosomesTiny particles that help to fold and

package DNA so it can fit inside the nucleus

If all of the DNA in one human cell were laid out end to end, it would be almost 2 meters long!

QUESTION:How does DNA replicate?

Semiconservative Replication1. Enzymes separate the 2

strands2. New strands are

synthesized3. This occurs during the

“S” phase of the cell cycle

Why must DNA be replicated?

When a cell divides, each new cell needs a copy of the genetic material

Semiconservative Replication

A DNA strand that looks like…

A T A G C G C A T T A CT A T C G C G T A A T G

…can be untwisted, broken apart, and have new nucleotides paired with BOTH of the original sides, forming 2 new strands. After the DNA strand is replicated it will look like this:

A T A G C G C A T T A CT A T C G C G T A A T G

A T A G C G C A T T A C T A T C G C G T A A T G