original question: which molecule contains genetic information?
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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
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